I

C A programming lan­ dous numerical capabilities "vith the graphi­guage designed for the cal analysis techniques of desktop computers UNIX operating system as a to produce complete, easy-to-use compllter successor of a language software for designing and simulating con­named B, and known for its compactness, memory con­servation, and power. C allows bit mapping and

str~ng typing. CII Cold junction; the reference junction of a

thermocoupIe. C++ A superset of the C programming lan­

guage that provides object-oriented features (objects, services, data abstraction, inherit­ance, sets).

C power supply An electrical power supply that is connected between the cathode and grid of a vacuum tube to provide a grid-bias voltage.

CAAA Clean Air Act bmendments of 1990 in United States which expand EPA enforce­ment powers a~nd place restrictions on air toxins, ozone- depleting chemicals, station­ary and mobile emissions sources, and sub­stances implicated in global warming and acid rain formation.

CAA Clean Air Act; United States federal law calling for air pollutant emissions standards for motor vehicles and stationary sources; first passed in 1970, reauthorized in 1977 and 1990.

cable 1. A large, strong rope made of fiber or wire. 2. A rope or chain used to restrain a ves­sel at its mooring. 3. A composite electrical conductor that consists of one or more solid or stranded wires, usually capable of carrying relatively large currents. It is covered with insulation, and the entire assembly is encased in a protective ovenvrap. The cables most commonly used for data highway systems are coaxial and twinaxial (shielded twisted­pair), but fiber-optic and multiconductor cables are also available.

cable entry (cable gland) A device that per­mits an electric cable to be introduced in-to an electrical apparatus. [ANSI/ISA-12.01.01­1999]'f

I cache memory A small, high-speed memoryI� that is placed between the slower main mem­

ory and the processor of a computer. A cache increases effective memory transfer rates and processor speed. It contains copies of data

II recently used by the processor and fetches

several bytes of data from memory in antici­pation of the processor accessing the n.ext sequential series of bytes.

trol systems. cadmium plating An electroplated coating of

cadmium on a steel surface that resists atmo­spheric corrosion. Applications include nuts, bolts, screws, and many hardware items in addition to enclosures.

c\lge A part of a valve trim in a globe or angle body that surrounds th~'closllre melnber and whose t10w passages may provide flow char­acterization and/or a seating surface. It may also provide stability, guiding, balance, and alignment, in addition to facilitating the assembly of other parts of the valve trim. [ANSI/ISA-75.05.01-2000] 2. A circular frame for maintaining uniform separation between balls or rollers in a rolling-element bearing. Also known as separator.

cage guide A valve plug fitted to the inside diameter of the cage to align the plug with the seat. [ANSI/ISA-75.05.01-2000]

calcine 1. To heat a material such as coke, limestone, or clay without fusing it, for the purpose of qecomposing compounds such as carbonates and driving off volatiles such as moisture, trapped gases, and water of hydra­tion. 2. To heat a material under oxidizing conditions. 3. The product of a calcining or roasting process.

calculating action A type of control system action in which one or more feedback signals are combined with one or more actuating signals to provide an output signal that is some function of the combination.

calculation A group of nun1bers and mathe­matical symbols that is executed according to a series of instructions.

calculus of variations The theory of maxima and minima of definite integrals "vhose inte­grand is a function of the dependent vari­ables, the independent variables, and their derivatives.

calibrate To ascertain the outputs of a device corresponding to a series of values of the quantity, which the device is to measure, receive, or transmit. Data so obtained are used to (a) determine t11e locations at vvhich scale graduations are to be placed, (b) adjust the output to bring it to the desired value, within a specified tolerance, and (c) ascertain the error by comparing the device output reading against a standard. [ANSI/ISA-51.1­1979 (1<1993]

CAD Computer-aided design; computer­ calibrated airspeed The airspeed of an air­aided drafting. Package that couples tremen- craft as read from a differential-pressure air­

65�

I

calibrating tank / calibration traceability

speed indicator that has been corrected for ing output readings, over the full (or instrument and installation errors. The read­ specified portion of the) range of a trans­ing equals true airspeed at standard sea-level ducer in an ascending and descending direc­temperature and pressure. tion. [ISA-37.1-1979 (RI982)] 3. The frequen­

calibrating tank A liquid vessel of known capacity that is used to check the volumetric accuracy of positive-displacement meters. Also known as "meter-proving tank."

calibration 1. A test during vvhich known values of a measllrand are applied to the transducer and the corresponding output reading are recorded under specified condi­tions. [ISA-37.1-1975 (RI982)] 2. The capabil­ity to adjust the instrument to "zero" and to set the desired "span." [ANSI/ISA-12.13.01­2000] 3. The procedure used to adjust the instrument for proper response (e.g., zero level, span, alarm, and range). [ISA-92.02, 03/ 04 and 06.01-1998.] 4. The determination of the experimental relationship between the quantity being measured and the output of the device that measures it. The quantity measured is obtained through a recognized standard of measurement. 5. For vibration, a transducer is subjected to a known motion, usually on a shaker table, and the output readings are verified or adjusted.

calibration constant In vibration, the sensi­tivity of a transducer within its linear range, expressed as a ratio of millivolts per vibra­tion amplitude. Typical units are millivolts per g/ millivolts per inches per second, and millivolts per n1il.

calibration curve 1. A graphical representa­tion of the calibration report. [ANSI/ISA­51.1-1979 (RI993); ISA-37.1-1975 (1982)] 2. A graph of the performance of a turbine flow­meter, showing sensitivity as the ordinate and volume flow, flowmeter frequency, or frequency divided by kinematic viscosity as the abscissa, for a liquid of specified density, 'viscosity, and temperature. [ISA-RP31.1­1977] 3. A plot of indicated value versus true value used to adjust instrument readings for inherent error. A calibration curve is usually determined for each calibrated instrument in a standard procedure, and its validity is con­firmed or a new calibration curve deter­mined by periodically repeating the procedure.

calibration cycle 1. The application of knovvn vallIes of the measured variable and the recording of the corresponding values of out­PLlt readings, over the range of the instru­ment/ in ascending and descending directions. [ANSI/ISA-51.1-1979 (R1993)] 2. The application of known values of a mea­surand, and the recording of the correspond-

cy that a device is due for calibration. This cycle could be dependent on calendar, cycles, or hours.

calibration gas 1. A gas with known concen­trations of components that is used as a stan­dard for calibration of analyzers. 2. The known concentrati9D(s) of gas used to set the instrument span or alarm level(s). [ANSI/ ISA-92.02.01, Part 1-1998; ANSI/ISA­92.03.01-1998; ANSI/ISA-92.04.01, Part 1­1996; ISA-92.06.01-1998]

calibration record A record (e.g., table or graph) of the measured relationship of the transducer output to the applied rneasurand over the transducer range. Note: Calibration records may contain additional calculated points so identified. [ISA-37.1-1975 (R1982)]

calibration report A table or graph of the measured relationship of an instrume11t as compared over its range against a standard. [ANSI/ISA-51.1-1979 (R1993)]

calibration simulation provisions Electrical connections or circuitry, contained within a transducer, that are designed to permit the calibration of the associated measuring sys­tem by causing output changes of known magnitude vvithout varying the applied mea­surand. [ISA-37.1-1975 (RI982)]

calibration standard A reference device used for calibrating equipment or instruments to the proper operating specifications. Primary standards are maintained by the National Institute of Standards and Teclmology in the U.S. Devices that have been certified, using the NIST primary standards, are called sec­ondary standards.

calibration system A complete system for calibrating turbine flo\vmeters, consisting of liquid storage, pumps, and the filters; t1ow, pressure, and temperahlre controls; the quantity-measuring apparatus; and the asso­ciated electronic instruments. [ISA-RP31.1­1977]

calibration test A test using known weights and forces to load the scale in order to deter­mine the performance of a belt-conveyor scale. [ISA-RP74.01-1984]

calibration traceability The process of relat­ing the calibration of an instrument through a step-by-step process to an instrllment or group of instruments that have been cali­brated and certified by a national standardiz­ing laboratory. [ANSI/ISA-51.1-1979 (1993)]

66

I

calibration uncertainty I cam-type timer

Note: The estimated error incurred in each member knovvn as a follower that slides or step must be known. rolls along a shaped surface or in a groove

calibration uncertainty The maximum calcu­ that is an integral part of the cam. A cam is lated error in the output values, shown in a usually a rotating plate that is eccentrically calibration record, for reasons that cannot be attributed to the transducer. [ISA-37.1-1975 (R1982)]

calibrator An instrument or system that veri­fies the accuracy of an instrument by com­paring it with an internal or external

.' calibration standard. caliper A gauging aevice with at least one

adjustable javv that is used to measure linear dimensions such as lengths, diameters, and thicknesses.

callI. To transfer control to a specified closed subroutine. 2. In communications, the action performed by the calling party, the opera­tions that must occur to make a call, or the effective use of a connection between two stations.

calling sequence The specified arrangement of instrllctions and data needed to set up and call a given subroutine.

calorie The mean calorie is 1/100 of the heat required to rais~ the temrerature of 1 gram of water from 0 C to 100 C at a constant atmospheric pressure. It is about equal to the quantity of heat required to r~i~~ 1 gram ?f water 1 C. A more recent defmltlon of a calo­rie is 3600/860 joules, a joule being the amount of heat produced by a watt in one second.

calorific value The number of heat units lib­erated per unit of quantity of a fuel burned in a calorimeter under prescribed conditions.

calorimeter 1. A device for determining the amount of heat liberated during a chemical reaction, change of state, or dissolution pro­cess. 2. An apparatus for determining the cal­orific value of a fllel. 3. An instrument or detector that measures the amount of heat in a light beam-used to measure incident radi­ation if the percentage of absorbed radiation is known.

calorimetric analyzer See caloril1leter. calorimetric detection A detector that oper­

ates by measuring the amount of heat absorbed. Incident radiation must be absorbed as heat to be detected.

calorize To prodllce a protective coating of aluminum and alunlinum-iron alloys on iron or steel (or, less commonly, on brass, copper, or nickel). The calorized coating is protective at temperatures up to about l,800

o

P. cam A machine element that produces com­

plex, repeating translational illotion in a

67

mounted on an axis perpendicular to the plate surface, with the follower resting against the contoured periphery of the plate. Alternatively, it may be a rotating cylinder or reciprocating plate with a groove cut into its surface for the follo\ver to rest in, or it may be some oth~f shape. ~ .

CAMAC Computer-a·utomated meaSllre­ment and control. A standard multiplexing interface, developed by the European nuclear community and widely used to con­nect instruments and transducers to comput­ers.

CAMAC Computer-automated measure­ment and control; instrumentation interface standard, developed in 1970s by users of the European nuclear physics community, that was promoted for industrial process control.

camber 1. Deviation from a straight line/ most often used to describe a convex/ edge­wise sweep or curve. 2. The angle of devia­tion from the vertical for the steerable wheels of an automobile or truck.

camera tube An electron-beam tube in which an optical image is converted into an elec­tron-current or charge-density image that is scanned in a predetermined pattern to pro­vide an electrical output signal. This output signal corresponds to the intensity of the scanned image. The part of a television cam­era that converts the optical image of the scene to be transmitted into electrical video signals. The two basic types of tubes are image orthicon and vidicon tubes/ from which many others have been developed.

cam follower The output link of a cam mech­anism.

campaign A limited run of product through process. A campaign can last fron1 days to months. The term is typically used in the chen1ical industry. Control strategy and physical process changes may accompany a campaign.

Campbell bridge A type of AC bridge that is used to measure the mutual inductance of coil or another inductor in terms of a mutual inductance standard.

camshaft The rotating member that drives a cam.

cam-type timer Any of several designs of timing devices that use a single contoured cam to continually adjust a process parame­ter/ such as a set point. SUCll timers may also employ several cams mo¥nted on a single

I

CAN /CAPE

timer shaft to provide interlocked sequence cantilever A beam or other structural mem­control of a complex operation without using ber that is fixed at one end and hanging free relays. at the other end.

CAN Controller area nehvork; developed by capabilities file A capabilities file describes Intel and I~obert Bosch Gmbh for real-time automotive industry needs. Primarily Euro­pean, it provides data link for J1939 used with off-road construction, agricultural, and other vehicles; often llsed on top of EIA 485, more recently on ISO DIS 11898. Allen-Brad­ley, with twenty other companies in 1994 promoted DeviceNet on top of CAN; Honey­well promoted MICROSWITCH using SDS on top. Also, short for cancel, character in dig­ital communications indicating that data pre­ceding it is in error and should be ignored.

can A metal vessel or container that is usually cylindrical and usually has an open top or .; removable cover.

candela A metric unit for luminous intensity. The unit used to express the in£ensity of light visible to the human eye. It corresponds to the emission from 1 j 60th of a square centi­meter of a black bcdy operating at the solidi­fication temperature of platinum and emitting one lumen per steradian.

candlepower An obsolete unit of measure for luminous intensity.

canned 1. Describing a pump or motor that is enclosed within a watertight casing. In the case of a motor, this casing is usually enclosed within the same casing as the driven element (SliCh as a pllmp) and designed so that its bearings are lubricated by the pumped liquid. 2. Describing a com­posite billet or slab that consists of a reactive metal core encased in metal, which is rela­tively inert so that the reactive metal may be hot worked in air by rolling, forging, or extrusion without excessive oxidation.

canned configurable software Computer software that is designed for a specific func­tion, based on general principles, and applied to many applications to achieve some desired capability of a computer sys­tem, for example, process control systems, spreadsheets, historical data collection sys­tems, statistical process control systems, and soon.

cannibalize To disassemble or remove parts from one assembly and use the parts to repair other, similar assemblies.

canonical form A form of matrix to which all members of a certain class of matrices can be reduced by transformation. For instance, any symmetric matrix can be reduced to a diago­nal matrix.

the communication objects in a fieldbus device. A configuration device can use device description (DO) files and capabilities files to configure a fieldbus system without having the fieldbus devices online. ._

capacitance 1. The ability of a condensor to N

store a charge before the terminals reach a potential difference of one volt. The greater the capacitance, the greater the charge that can be stored. 2. The anlOllnt of energy or material that must be added to a closed sys­tem to cause unit change in potential. hence, the partial derivative of the content with respect to poter~ial.

capacitance meter An instrument for deter­mining the electrical capacitance of a circuit or circuit element. See also microfaradnleter.

capacitive Wh~n ,used as a third modifier per ISA-37.1-1975 (RI982), capacitive means con­verting a change of measurand into a change of capacitance. [ISA-37.1-1975 (RI982)]

capacitive instrument A ll1.easuring device whose o,utput signal is developed by varying the capacitive reactance of a sensitive ele­ment.

capacitor A device used for storing an electri­cal charge and designed to hold voltage for a limited time.

capacitor start/capacitor run motor An AC motor used for hard-starting loads. It fea­tures a high capacitor for starting the motor and a low capacitor for running the motor. Start-up and running windings are always energized, and a centrifugal s\vitch changes the connection between high and low capaci­tors.

capacity [Proc] 1. In process control, the rate of flow throug11 a valve, usually stated in terms of Cy or Kyo [ANSIjISA-75.05.01-2000] 2. A measure of the maximum quantity of energy or material that can be stored within a given piece of equipment or system. [Comp] 3. In computing, information storage capability, usually given in bytes (KB, MB, GB).

capacity factor T11e ratio of the average load carried to the maximum design capacity.

capacity lag In any process, the affiOllnt of time it takes to supply energy or material to a storage element at one point in the process from a storage point elsewhere in the pro­cess. Also kll0v\rn as transfer lag.

CAPE Concurrent art-to-product environ­ment; compliter-aided design tools used for

68

I

cap height / carburizing

(dra\\ling) "concept-to-finished-product" bon equivalent, TC is the total carbon con­efforts. tent, Si is the silicon content, and P is the

cap height In the typographical composition phosphorus content, all in wt%. For weld­of screen displays and printing, the height of ability, the formula is CE =C + Mn/6 + (Cr + a capital letter measured from baseline to top.

capillary 1. Having a very small internal diameter. 2. A tube \vith a very small diame­ter.

capillary action Spontaneous elevation or depression of a liquid level in a fine hairlike tube \tvhen it is dipped into a body of the liq­uid. Capillary action is induced by differ­ences in surface energy bet\veen the liquid and the tube material.

capillary drying The progressive removal of moisture from a porous solid by evaporation at an exposed surface followed by movement by capillar action of the liquid from the inte­rior to the surface until the surface and core reach the same stable moisture concentra­tion.

capillary tube A tube that is sufficiently fine such that capillary action is significant.

CAPISCE Computer architecture for produc­tion information systems in a competitive environment; project funded by ESPRIT to unite three layers of manufacturing architec­ture (planning, execution, and control); first effort by major elM vendors toward seatn­lessly integrating information from control systems into business planning systems.

CAPP Computer-aided process planning; data management framevYork designed to assist functions of process planning.

caps In the typographical composition of screen displays and printing, capital letters in the particular type font chosen.

cap screw A threaded fastener similar to a bolt, but generally used without a nut. It is threaded into a tapped hole in one part of an assembly.

capstan A vertical-axis drum llsed for pulling or hauling. It may be power driven, or it may be turned manually by means of a bar extending radially from a hole in the drllm.

capsule A pressure-sensing element consist­ing of two metallic diaphragms joined around their peripheries. [ISA37.1-1975 (RI982)]

carbon An element. The principal combusti ­ble constituent of all fuels.

carbon equivalent An empirical relationship that is used to estin1ate the ability of a metal to produce gray cast iron. Also a~1 empirical relationship that is used to rate the weldabil ­ity of alloy steels. For cast iron, the formula is CE = TC + 1/3(Si + P), where CE is the car-

Mo + V)/5 + (Ni + Cr)/15, where each sym­bol stands for the concentration of the indi­cated element in wt%.

carbonitriding A surface-hardening process in which a suitable ferrous material is heated ilt a temperatllre above the lo\ver transfor­matiort"tempera.ture in;an atmosphere that will cause the simultaneous absorption of carbon and nitrogen at the surface and, by diffllsion, create a concentration gradient. Final properties are achieved by controlled cooling through temperature and sometimes through sllbsequent tempering.

carbonization The process of converting coal into carbon by removing other ingredients.

carbon loss The loss that represents the unliberated thermal energy that is occa­sioned by the failure- to oxidize some of the carbon in the fuel.

carbon-pile pressure transducer A resis­tive-type pressure transducer that depends for its operation on the change in resistance that occurs when irregular carbon granules or smooth carbon disks are pressed together. Because of its low resistance, carbon-pile pressure transducers can often provide suffi­cient output Cllrrent to actuate electrical instruments withollt needing amplification.

carbon potential A measure of the ability of an environment to alter or maintain the sur­face-carbon content of ferrous alloys. The specific effect that occurs depends on tem­perature, time, and steel composition as well as on carbon potential.

carbon steel An alloy of carbon and iron that contains not more than 2 percent carbon and that contains no alloying elements other than a small amount of manganese.

carburetor A component of a spark-ignition internal combustion engine that mixes fuel with air, in proper proportions, and delivers a controlled quantity of the mixture to the cYlinders.

carburizing A surface-hardening process in which a suitable ferrous material is heated at a temperature above the transformation range in the presence of a carbon-rich envi­ronment. This carbon-rich environment may be produced from solid carbon, vaporized liquid hydrocarbons, or gaseous hydrocar­bons. After the production of a carbon con­centration gradient in the alloy/ the ferrous material is either qllenched from the carbur­izing temperature and tempered or reheated,

69

card / cascade

quenched, and tempered to achieve the desired properties in both the carbon-rich outer case and the carbon-lean inner core.

card A circuit board within a computer or other electronic instrument or system.

card hopper See hopper, card. card reader (Hollerith cards) A hardware

device for reading computer-standard punched cards for computer entry. This device was ubiquitous in the early days of computing but is now rarely used.

card stacker See stacker, card. carpal tunnel syndrome The irritation of the

tendon sheath and lining around the median nerve at the human wrist. Carpal tunnel syn­drome can affect typists, computer operators, and anyone who uses hand tools.

carriage 1. A mechanism that moves along a predetermined path in a machine in order to carry and position another component. 2. A mechanism designed to hold paper in the active portion of a printing or typing machine and to advance the paper as neces­sary. Sometimes, the mechanism also auto­matically feeds new sheets of paper on demand.

carriage bolt A threaded fastener with a plain (unslotted) head and a sqllare shoulder below the head that keeps the bolt from turn­ing as the nut is tightened. This type 0fbolt is designed primarily for bolting wood mem­bers/ but can be used with metal members if the one next to the bolt head has a square bolt hole to accommodate the bolt's shoulder.

carriage return The operation that causes printing or typing to be returned to the left margin of a page or screen with or without a line advance. Sometimes used to indicate that manual data entry has been completed.

carriage return character (CR) A format effector that callses the location of the print­ing or display position to be moved to the left margin with or without a line advance.

Carrier A continuous frequency signal that is capable of being modulated to carry infor­mation.

carrier band A single-channel signaling tech­nique in which the digital signal is modulated on a carrler and transmitted. It transmits and receives on the same frequency. Also, see phase coherent frequency shift keying (FSK).

carrier detect A modem interface signal defined by the RS-232 standard that indicates to a receiving device that a signal is coming from a distant modem.

carrier frequency The basic frequency or pulse repetition rate of a transmitted signal. It bears no intrinsic intelligence until it is

modulated by another signal that does bear intelligence.

carrier insertion In digital comn1unications, a media access protocol method (ISO data link layer 2) whereby a station in the network monitors the message stream of all messages passing throug11 it until it detects a lull in traffic. It then inserts its own message while btlffering and later retransmitting any addi­tional incoming messages. Also known as ring expans~on .bec~use the method"expands" . ­the ring of data By:one message until the . original message or acknowledgment by the receiving station returns to the sender.

Carrier Sense Multiple Access with Collision Detection (CSMAlCD) A method of con­trolling multiaccess computer networks in which each station on the network senses traffic and waits for it to clear before sending a message. Two devices that try to send con­current m~ssages must both step back and try again. CSMA/CD is used as a media access method (ISO data link layer 2) for local area networks (LANs).

carrier-to-noise ratio Carrier amplitude divided by noise amplitude, or carrier power divided by noise power.

carryover The chemical solids and liquid that are entrained with the steam from a boiler.

cartridge A small unit used for storing com­puter programs or data values. The amount of information it stores tends to be small and access times large in comparison with disks.

cartridge disk A relatively low-capacity data or program-storage medium. Generally removable.

cartridge tape A small magnetic tape for stor­ing digital programs. Stores discrete records.

CASE Common Applications Session Ele­ment. Also, computer-aided software engi­neering; the use of object-oriented programming and other techniques to streamline the generation of programming code as well as to access information from a relational data base. Also, conformity assess­ment systems evaluation; vollintary program for NISI to check the competency of manu­facturers, testing groups, standards groups, trade associations, or other organizations involved in qualit:: assurance.

CAS number A number assigned to specific chemicals by the Chemical Abstracts Service. In most cases, these numbers are unique numerical identifiers. In others, this item may show a "mixture" of chemicals within some product.

cascade 1. A series of amplifiers in which the output from one amplifier is connected to the

70

inptlt of the next. 2. A series of stages in which the output of one stage is the input of the next.

cascade control 1. Control action in which the au tput of one controller is the set point for another controller. [ANSI/ISA-77.42.01-1999] 2. A control system composed of two loops where the set point of one loop (the inner loop) is the output of the controller of the other loop (the outer loop). 3. A control tech­nique that.in<;:orporates a master and a slave loop. The master loop controls the primary control parameters and establishes the slave-loop set point. The purpose of the slave loop is to reduce the effect of disturbances on the primary control parameter and to improve the dynamic performance of the loop. See control, cascade.

OVERALL PROCESS

cascade control action Control action in which the output of one controller is the set point for another controller.

cascade control system A control system in which the output of one controller (the outer loop) is the set point for another controller (the inner loop). The outer loop is normally a slow-responding process as compared to the inner loop. [ANSI/ISA-77.44-1995]

cascading In communications, connecting twisted-pair hubs by running a twisted-pair cable from one hub to another.

case 1. An enclosllre that is designed to hold one or more components in a fixed position, usually by nestling one component into a conforming recess or resting it on fixed sup­ports. In some instances, components are attached directly to the enclosure. The entire unit may be kept in storage or taken to a job site and the contents removed as needed. Sometimes as with certain portable instru­ments, the contents can be used by merely opening the cover of the enclosure and mak­ing appropriate connections to the device inside. 2. A hardened outer layer on a ferrous alloy that is produced by suitable heat treat­ment, which sometimes involves altering the chemical composition of the outer layer before hardening.

cascade control! catalog

case hardening Producing a hardened alIter layer on a ferrolls alloy by any of several sur­face-hardening processes, including carbur­izing, carbonitriding, nitriding, flame hardening, and induction hardening. Also known as surface hardening.

case pressure See burst pressure rating, proof pressure, or reference pressure. [ISA-37.1-1975 (R1982)]

casing- A coveri11g consisting of sheets of metal or other material- such as fire-resistant composition board that~'"is' used to enclose all or a portion of a steam-generating unit.

cassette 1. A light-tight container for holding photographic or radiographic film or a pho­tographic plate thCit is positioned within a camera or other device for exposure. 2. A small, compact container that holds magnetic tape and supply and takeup reels and that can be quickly inserted and removed as a llnit from a tape recorder or playback machine. Different sizes and styles of tape and cassette are used for audio, video, and computer applications, depending on the hardware being used.

cassette tape Magnetic tape used for digital data storage.

cast 1. To produce a solid shape from liquid or semisolid bulk material by allowing it to harden in a mold. 2. A tinge of a specific color. A slight overtint of a color that is dif­ferent from the main color-for instance, white with a bluish cast.

caster 1. The fore-and-aft angle of deviation from the vertical of the kingpin (or its equiv­alent) in an automobile- or truck-steering gear. 2. A wheel, usually small in diameter, that is mounted so it is free to swivel about a vertical axis. It is commonly used to support hand trucks, machinery, or furniture.

casting 1. The process of making a solid shape by pouring molten metal into a cavity, or mold, and allowing it to cool and solidify. 2. A near-net-shape object produced by this process. A rOllgh casting that is cylindrical, square, or rectangular in cross section and intended for subsequent hot working or remelting. Also called an "ingot."

cast iron Any iron-carbon alloy that contains at least 1.8 percent carbon and that is suitable for casting to shape.

CAT Catalog; chemical addition tank; com­puter-aided test; computer-assisted training; Cllrrent Adjllsting Type process control out­put (4-20 rnA).

catalog� In data processing, the contents of a computer disk or tape.

71�

I

catalysis / cavitation

catalysis A phenomenon in which a rela­tively sn1all amount of a substance augments the rate of a chemical reaction without itself being consumed.

catalyst A substance that alters the velocity of a chemical reaction and that may be recov­ered essentially unaltered in form and amount at the end of the reaction.

cataphoresis The movement of suspended solid particles il1 a liquid medium because of the influence of electromotive force.

catastrophic failure 1. A sudden failure that occurs without prior warning, as opposed to a failure that occurs gradually by degrada­tion. 2. The failure of a mechanism or compo­nent that renders an entire machine or system inoperable.

catenary The shape that is produced by hold­ing a rope or cable at its ends and allowing the center section to sag under its own weight.

cathetometer An optical instrument for mea­suring small differences in height-for instance, the difference in height between two columns of mercury.

cathode 1. The metal plate or surface that acts as an electron acceptor in an electrochemical circuit. 2. The positive electrode in a storage battery or the negative electrode in an elec­trolytic cell. 3. The negative electrode in an X-ray tube or vacuum tube where electrons enter the interelectrode space.

cathode corrosion 1. Corrosion of the cath­ode in an electrochemical circuit, usually involving the production of alkaline corro­sion products. 2. Corrosion of the cathodic member of a galvanic couple.

cathode follower A type of electronic circuit in which the outpllt load is connected in the cathode circuit of an electron tube or equiva­lent transistor. Also, the input signal is impressed across a terminal pair in which one is connected directly to the control grid and the other is connected to the remote end of the output load.

cathode ray In an electron tllbe or similar device, a stream of electrons emitted by the cathode.

cathode ray oscillograph An instrument that produces a record of a waveform by photo­graphing its graph as produced on a cath­ode-ray tube, or by otherwise recording such an image.

cathode ray oscilloscope An instrument that indicates the shape of a waveform by pro­ducing its graph on the screen of a cath­ode-ray tube.

cathode ray tube (CRT) 1. An electronic vac­uum tube that contains a screen on vvhich information may be stored for visible display by means of a multigrid modulated beam of electrons from the thermionic emitter. Stor­age is effected by means of charged or uncharged spots. 2. A storage tube. 3. An oscilloscope tube. 4. A pictllre tube. 5. A computer terminal that uses a cathode ray tub~ as a display device.

cathodi--c coating A mechanical plate or elec­trodeposif ~n?t ~ase metal, where the coating is cathodic to th"e" u11derlying base metal.

cathodic protection Preventing the electro­chemical corrosion of a metal object by mak­ing it the cathode of a cell that uses either a galvanic or impresse~ current.

cathodoluminescence Luminescence that:is .~.... :~

induced by exposure of a su"itable material to " cathode rays.

caulk 1. A he~1,vy paste, such as a mixture of a synthetic or rubber compound and a curing agent or a natural product such as oakum, that is used to seal cracks or seams and make them airtight, steam tight, or watertight. Also known as "caulking compound" or "calk." 2. To seal a crack or seam "vith caulk.

caustic dip A strongly alkaline solution for immersing metal parts in order to etch them, to neutralize a11 acid residue, or to remove organic material such as grease or paint.

caustic embrittlement The intergranular cracking of carbon steel or Fe-Cr-Ni alloy when it is exposed to an aqueous caustic solution at a temperature of at least 150°F while it is stressed in tension. A form of stress-corrosion cracking. Also known as "caustic cracking."

caustic soda The most important of the com­mercial caustic materials. It consists of sodium hydroxide that contains 76 percent to 78 percent sodillm oxide.

Cavendish balance A torsional instrument for determining the gravitational constant. The displacement of t"vo small spheres of known mass mounted on opposite ends of a thin rod suspended on a fine wire is mea­sured when hvo large spheres of known mass are brought near the small spheres.

cavitation A two-stage phenomenon of liq­uid flow. The first stage is the formation of vapor bubbles within trle liquid system because of the static pressure of fluid falling belo\v the fluid vapor pressllre. The second stage is the collapse or implosion of these cavities back inJo an all-liquid state as the fluid decelerates and static pressure is recov­

72

• •

I

cavitation erosion / CDPD�

ered. [ANSI/ISA-75.05.01-2000; ISA­ the manufacturer vvho makes that product. RP75.23-1995] See also NCB.

cavitation erosion The progressive removal CBDS Connectionless broadband data ser­of surface material as a result of localized vice; definition of which is emerging from hydrodynamic impact forces that are associ­ated with the formation and subsequent col­lapse of bubbles in a liquid that is in contact with the damaged surface. Also known as "cavitation damage" and "liquid-erosion failure."

cavitation index The value for the operating service conditions of a valve, expressed as 5

and numerically equal to (P 1 - P v ) / (P 1 - P 2 ).

[ISA-RP75.23-1995] cavitation level The degree to which cavita­

tion is occurring, tllat is, incipient, constant, incipient damage, choking, or maximum vibration. These levels can be determined by testing for vibration, pitting, or metal loss as well as for changes in valve capacity (Cv ).

· .[ISA-RP75.23-1995]

zo -­~ ~ W ...J

\0W U� U� «

SUPER- FULL INCIPIENT ---~ CAVITATION j CAVITATION CAVITATION CAVITATION

cr = (P 1 - P v ) /AP

cavity resonator A space nornlally enclosed by an electrically conducting surface that is used to store electromagnetic energy and whose resonant frequency is determined by the shape of the enclosure.

cavity-type wavemeter An instrument that is used to determine frequency in a waveguide system. Typically, the position of a piston inside a cylindrical cavity is tuned to reso­nance, which is determined by a drop in transmitted power. The meter is then detuned for normal operation.

CB Certification board; certificate issued by National Certification Board (NCB) to pro­vide assurance to the end user that claims of product performance have been verified by an independent party, attesting to the quality and safety of that product. Differs from Euro­pean CE Mark in vvhich testing is done by

the European Telecommunications Stan­�dards Institute; expected to be equivalent to� and compatible vvith SMDS. See SMOS.�

CCD Charge-collpled device; charge transfer device that consists of an array of MOS capacitors designed so charges can be moved through the semice>nductor substrate in a controlled manner. Esseri~ially a shift regis­ter, it can be used to form analog or digital serial memories, can function as a dynamic filter, and can be used for imaging as in solid­state cameras, etc. See MOS.

CCITT Comite Consultatif Internationale de Telegraphie et Telephonie (France). Consul­tative Committee for International Tele­phony and Telegraphy [Comite Consultatif Internationale de Telegraphie et Telephonie]; international association that sets worldwide communications standards, such as V.21, V.22, X.25, etc. Replaced by ITU-TSS (Interna­tional Telegraphic Union-Teleconlffiunica­tions Standards Sector).

CCITT V.XX (Consultq.tive Committee for International Telephony and Telegraphy) International standards in communications that are concerned with modem interfaces, speeds, and transmission modes (i.e., V.22).

CCITT X.25 (Consultative Committee for International Telephony and Telegraphy) An international standard that defines the protocol used to access a packet switching network.

CCL Connection control language; in com­puters linked through phone networks, a file that contains a list of commands the modem needs to work over a network to other "for­eign" modems.

COOl Copper-distributed data interface; unshielded twisted-pair, shielded twisted­pair, dual- grade tvvisted-pair options; see FDOl.

COF Compressed data format; method of saving data to electronic memory expressly for tlle purpose of exchanging data between computers.

COMA Code Division Multiple Access; in digital comnlunicatiorLs, a media access pro­tocol (data link layer).

CDPD Cellular digital packet data; one of the emerging wireless digital communications technologies useflll for true SCADA systems, CDPD sends packets of data using existing cellular communications technology for a given region. While cost is still a constraining

73�

I

CDR / centimeter-gralll-second (CGS)�

factor with CDPD, this technology has respectively, of pure water at standard pres­�proved effective for regions without direct sure.� telephone or leased lines. See also SCADA. cement 1. A dry, powdery mixture of silica,�

CDR Critical design review; used to identify alumina, magnesia, lime, and iron oxide that issues in final design release; compare POR.

CD-ROM "Compact disk, read-only mem­ory." A compact disk used for computer data storage.

CDTV Commodore Dynamic Total Vision; consumer multimedia from Commodore, which includes CD-ROM/CD audio player, Nlotorola 68000 processor, 1 MB RAtv1 and ten-key infrared remote control.

CEB, CEBus Consumer Electronic Bus; EIA draft (9/93) to integrate utilities, sensors, controls, and communications in the home. Also, Comite Electrotechnique BeIge; Belgian member of (Belgiun1IEC).

CEF Comite Electrotechnique Fran<;ais (France); French member of IEC.

CEI Comitato ElettrotecnicoJtaliano (Italy); Italian member of IEC.

ceilometer A recording instrument for auto­matically determining cloud heights.

cell [Eng] 1. In engineering, one of a series of chambers in which a chemical or electrochem­ical reaction takes place-for example, the chambers of a storage battery or electrolytic refining bath. 2. One of the cavities in a honey­comb structure. 3. In manufactl1ring, a'.. cluster of operations for performing a single func­tion in an assembly line (such as, "drill, then tap a set of holes, bolt on mounting bracket, attach device"). [Comp] 4. In computing, a storage location for one unit of information, usually one character or one word. Specific terms such as column, field, location, and block are preferable when appropriate. See storage cell.

cell constant In conductivity measurement, the ratio of conductance electrodes to area of electrode surface.

cell container The container for the plate pack and electrolyte of a cell that is made of a material impervious to attack by the electro­lyte. [ANSI/ISA-12.16.01-1998 (IEC 60079-7 Mod)]

cell controller Typically, a programmable logic controller or an interconnected cluster of them for the purpose of performing opera­tions in a "cell" on the manufacturing line. The term is sometilnes broadened to include portions of process, but with varying inter­pretations.

Celsius A scale for measuring temperature that is based on the definition of 0 C and 100°C as the freezing point and boiling point,

hardens into a solid mass when mixed with water. It is one of the ingredients in concrete and mortar. 2. An adhesive for bonding S11r­faces for which intimate contact cannot be established and the adhesive must therefore fill a gap over all or part of the faying sur­fat:es..

cementation i. The high-temperature impregnation of a metal surface with another material. 2. The conversion of wrollght iron into steel by packing it in charcoal anti heat­ing it at about 1,800°F for 7 to 10 days.

CENELEC, CLC Comite Europeen de Normalisation Electrotechnique; its goals are similar to those of CEN, but focused on elec­trical and electronic products; European counterpart of IEC.

cent The interval between two sound fre­quencies, where the ratio of the two frequen­cies is the twelve-hundredth root of 2. Also equal to one-hundredth of a semitone.

center gauge .A gauge used to check angles, such as the angle of a cutting tool point or screw thread.

center of gravity 1. A fixed point in a mate­rial body through which the resultant force of gravitational attraction acts. 2. The point that represents the average position of matter in a body.

center of mass That point of a material body or system of bodies that moves as though the system's total mass existed at tl1at point and all external forces were applied at that point. Also known as "center of inertia" and "cen­troid."

center of seismic mass The point within an acceleration transducer at which acceleration forces are considered to be summed. [ISA­37.1-1975 (R1982)]

center-to-end dimension The distance from the center line of a valve bodY to the extreme plane of a specific end conne~tion. See face-to-face dimension and end-ta-end dimen­sion. [ANSI/ISA-75.05.01-2000]

centigrade A nonpreferred term formerly used to designate the scale now referred to as the Celsius scale.

centimeter-gram-second (CGS) A standard metric system of units that was used largely for scientific work before the adoption of the international 51 system, which is currently preferred for both scientific and engineering work.

74

centipoise (cp) / certification�

entipoise (cp) A unit of viscosity that is� equal to 0.01 poise.�

entistoke (cs) A CGS unit of kinematic vis­cosity in cllstomary use. It is equal to the kinematic viscosity of a fluid that has a dynamic viscosity of 1 centipoise and a den­sity of 1 gram per cubic centimeter. See centi­nleter-granl-second (eGS).

:entral-limit theorem The theorem that the� distribution of sample means taken from a� large· population approaches a normal� (Gaussian) Cllrve.�

:entralize To bring under one control; consol­idate.

:entralized maintenance shop One mainte­nance shop that has responsibility for n1ain­talning all equipment in the facility. Usually, several crafts work out of this one central­ized maintenance shop.

:entral office The main switching center for common carriers.

:entral processing unit (CPU) 1. The brain of the COIT,puting machine, usually defined by the arithmetic and logic units (ALU) plus a centrol section, often called a processor. 2. T11e part of a computing system that contains t}le arithmetic and logical units, instruction control unit, timing generators, and memory a.nd I/O interfaces. See also unit, central pro­I:essing.

central station A power plant or steam-heat­ing plant that generates power or steam for ~tale.

ceIltrifugal compressor A machine in vvhich ':.1 gas or vapor is compressed by radial accel­eration in an in1peller with a surrounding casing and that can be multistaged to achieve hjgh ratios of compression.

centrifugal control Speed control that uses sensors that respond to centrifugal force to sense speed.

centrifugal fan A fan rotor or wheel within a housing that discharges the air at a right angle to the axis of the \vheel.

centrifugal force A force that acts in a direc­tion both along and outward on the radius of turn for a mass in motion.

centrifugal pump A machine for moving a liquid by accelerating it radially outward in an impeller to a surrounding volute casing.

centrifugal switch A switch that is opened or closed by centrifugal force.

centrifugal tachometer An instrument that measures the instantaneous angttlar speed of a rotating member such as a shaft by measur­ing the centrifugal force on a mass that rotates with it.

centrifuge A rotating device that uses centrif­ugal force to separate suspended fine or col­loidal particles from a liquid or to separate two liquids of different specific gravities.

centripetal force For:e exerted inward toward the center of the rotation of an object moving in a circular path (the opposite of centrifugal force).

CEPEL Centro de Pesquisas de Energia Eletrica (Brazil); Brazilian certification and testing laborator~ for te~ing the equipment of different vendors to s'ome -common stan­dard.

ceramic 1. A heat-resistant natural or syn­thetic inorganic product made by firing a nonmetallic mineral. 2. A shape made by baking or firing a ceramic materiat such as brick, tile, or labware.

ceramic coating A protective coating made by thermal spraying a D1aterial slIch as alu­minum or zirconium oxide or by cementing a material such as aluminum disilicide on a metal sllbstrate.

ceramic transducer See electrostriction trans­ducer.

CERCLA Comprehensive Environmental Response, Compensation and Liability Act (also known as Superfund). United States federal law authorizing the identification and remediation of llnsupervised hazardous waste sites.

Cerenkov radiation Visible light that is pro­dllced when charged particles pass through a transparent medium at a speed exceeding the speed of light in the medium.

cermet A poyvder-metallurgy product that consists of ceramic particles bonded together with a metal matrix.

certificate of analysis A certifica tion of a product's or material's conformance to qual­ity standards or specifications. It may incltlde a list or reference of analysis results and process information. It is often required for the transfer of custody of materials. [ISA­95.00.01-2000]

certification 1. The act of certifying. 2. The state of being certified. 3. The certification of instrumentation and control technicians in nuclear power plants. The criteria of certifi­cation address qualifications based on educa­tion, experience, training, and job performance. The attainment of certification is a vvay for individuals to indicate to the general public, to co-workers, to en1ployers, and to others that an impartial, nationally recognized organization has determined that they are qllalified to perform specific techni­cal tasks by virtue of their technical knowl­

75�

certified / chain-float liquid-level gauge�

edge and experiences. Certification bestows a sense of achievement upon the certificant since it reflects professional advancement in achosen field.

certified A generic term that refers to appara­tus that has been evaluated by a recognized testing agency and confirmed to be in com­pliance with the applicable standard(s). Note: Some agencies use the terms approved, listed, or labeled to indicate compliance with the applicable standard. [ANSI/ISA­-12.01.01-1999]

certify 1. To confirm something formally as true, accurate, or genuine. 2. To guarantee something as meeting a standard. 3. To issue a license or certificate.

CESI Centro Elettrotecnico Sperirnentale Ital­iano (Italy); Italian certification and testing laboratory for testing the equipment of dif­ferent vendors to some common standard.

CFA CompactFlash Association; independent corporation of ten companies working to help create CompactFlash,standard: Apple, Canon, Eastman Kodak, Hewlett-Packard, Matsushita, Polaroid, NEC, SanDiak, Seagate, and Seiko Epson.

CFC chlorofluorocarbon; a consideration in EPA (United States) regulations; any com­pound containing carbon and one or more halogens, usually fluorine, chlorine, ot bro­mine. Used as a refrigerant and solvent and as a propellant in aerosol sprays. Those CFCs containing bromine are used in fire extin­guishers; CFCs have been identified as a cause of depletion of the Earth's protective ozone layer.

CFR engine Cooperative Fuel Research engine. A standard test engine for determin­ing the octane number of motor fuels,

CGA Color / graphics adapter(array); video standard (for IBM PC in 1981), offering 320 x 200 pixels vvith four colors, or 640 x 200 pix­els with two colors. In text mode, up to six­teen possible colors. See EGA, PGA, SVGA, UXGA, VGA, XGA. Also, continuous gas ana­lyzer.

CGI Compressed Gas Institute; COlnputer Graphics Interface;Common Gateway Inter­face, Internet web standard for methods llsed by servers, external programs, and scripts for intercommunication.

CGM(IF) COITlputer Graphics Metafile (Inter­change Format); standard for archiving and transferring graphics data.

CGMP Current good manufacturing practice; regulations by FDA for finished pharnlaceu­ticals.

CGRM Computer Graphics Reference Model; ISO/IEC JTCl/SC24 tools for computer graphics to ensure that application programs and pictures are portable.

CGS Centimeter-gram-second; system of fundamental units for mass, length, and time; novv obsolete, replaced by MKS system from which SI units are developed. See MKS.

chad The piece of m~terial that is removed when forming a hole or notch in a storage medium such as p~ched tape.or punched cards. [ISA-RP55.1-~.975(RI983)]

chafing fatigue See fretting. chain 1. A nonrigid series of metal links or

rings that are interlinked with each other or are pinned or otherwise held together in order to make an elongated flexible member that is suitable for pulling, hauling, lifting, sllpporting, or restraining objects or for transmitting power.. 2. A mesh of rods or plates that is used in place of a belt to convey objects or transmit power. 3. An organization in which record's or other items of data are strung together by means of pointers.

chain-balanced density meter A sub­merged-float 'meter that uses an iron-core float that moves up and down within a pickup coil. A slack chain attached to the bot­tom of the float applies more weight as the float rises and establishes a definite equilib­rium position for any given fluid density within the range of the instrument.

chain block A lifting tackle, often suspended from an overhead track, that uses a chain instead of rope to lift heavy weights and is hand driven by pulling on an endless chain. Some models are power driven. Also knovvn as chain fall and"chain hoist./I

chain drive A device for transmitting power and motion without slipping. It consists of an endless chain that meshes with driving and driven sprockets. Chain drives are used on bicycles and motorcycles to provide the motive power, on conveyors to drive the belts, and in hoisting mechanisms to provide the lifting power.

chain fall A method for manually operating remote valves by mechanically using chains and sprockets.

chain-float liquid-level gauge A device for indicating liquid level in a tank that consists of a float connected to a cOlmterweight by a chain running over a sprocket. as the float rises and falls with liquid level in the tank, the chain rotates the sprocket that in tllrn positions a pointer to indicate liquid level.

76�

I

chalking / characteristic, equal-percentage�

chalking A defect of coated metals that is channel sampling rate The number of times caused by the formation of a layer of pow­ a given data input is sampled during a speci­dery material at the metal-coating interface. fied time interval.

chamfer 1. A beveled edge that relieves an channel selector In an FM discriminator the otherwise sharp corner. 2. A relieved angular cutting edge at the tooth corner on a milling cutter or similar tool.

change control In process validations, a formal system by which qualified representatives of appropriate disciplines review proposed or . actual changes that might affect validated status. The intent is to determine the need for action that would ensure and document that the system is maintained in the validated state.

channell. A path along which signals can be sent, for example, a data channel or output channel. [ISA-RP55.1-1975 (R1983)] 2. The portion of a storage medium that is accessi­ble to a given reading station. [[ISA-RP55.1­1975 (R1983)] 3. In communication, a means for one-way transmission. Contrast with cir­cuit. [ISA-RP55.1-1975 (R1983)] 4. Sometimes called a point. [ISA-RP55.1-1975 (R1983)] 5. A collection of instrument loops, including their sensing lines, that may be treated or routed as a group while being separated ~,

from instrument loops assigned to other redundant channels. [ANSI/ISA-67.02-1999] 6. An arrangement of components and mod­ules so as to generate a single protective action signal when required by a generating stati~)n condition. A channel loses its identity where single-action signals are combined. [ISA-67.06-1984] 7. A path along which infor­mation, particularly a series of digits or char­acters, may flow. 8. One or more parallel tracks trea ted as a unit. 9. In a circulating storage, a channel is one recirculating path that contains a fixed number of \vords stored serially by word. 10. A path for electrical communication. 11. A band of frequencies used for communication. 12. An ungrounded conductor in a grounded, intrinsically safe circuit, or a conductor and its reference in a galvanically isolated intrinsically safe circuit. [ANSI/ISA-RP12.6-1995J

channel, input The analog data path between the field wiring connector or termination strip and the analog-to-digital converter or other quantizing device used in the sub­system. In typical subsystems, this path may include a filter, an analog signal multiplexer, and one or more amplifiers. [ISA-RP55.1­1975 (R1983)]

channel capacity The maximum data rate that can be transmitted over a channel.

77

plug-in module that causes the device t~ select one of the channels and demodulate� the subcarrier so as to recover data.�

channel service unit A line driver that inter­faces between a customer's data terminal equipment and boosts the signal to a Data­phone Digit~l S~rvice (DDS) digital network.

channel uncertainty (CD) The total amOllnt to \vhich an instrument channel's output is in doubt (or the allowance made therefore) because of unaccounted-for errors, either random or systematic. The uncertainty is generally identified witl)in a probability and confidence level. [ANSI/ISA-TR67.04.08­1996]

character 1. A predefined group of pixels. [ISA-5.5-1985] 2. One symbol of a set of ele­mentary symbols such as those correspond­ing to the keys on a typewriter. The syrrlbols usually include the decimal digits 0 through 9, the letters A through Z/ punctuation marks, operation symbols, and any other sin­gle symbols that a computer may read, store, or write. [ISA-RP55.1-1975 (R1983)] 3. The electrical, magnetic, or mechanical profile that is used to represent a character in a com­puter/ and its various storage and peripheral devices. A character may be represented by a group of other elementary marks, such as bits or pulses. [ISA-RP55.1-1975 (1983)]

character codes The binary code patterns used to create characters in a con1pllter.

character embossing The raising of the sur­face of a printing medium (such as paper) within the perimeter of a printer character as a result of the impact of a type element against that printing meliium. [ISA-RP55.1­1975 (R1983)J

character generation The production of typo­graphic images by using font master data that is generated to screens or output devices.

characteristic 1. The integral part of a com­mon logarithm. In the logarithm 2.5, the characteristic is 2 and the mantissa is 0.5. 2. Sometimes, that portion of a floating-point number that indicates the exponent. 3. A dis­tinctive property of an individual, document, item, and so on.

characteristic, equal-percentage The inher­ent flow characteristic that, for equal incre­ments of rated travel, will ideally give equal

characteristic, flow I charge�

percentage changes of the existing flow coef­ficient (e z,). [ANSI/ISA-75.05.01-2000]

100,.....--------------,

I ~ 80 0

~ T5 60m c. m U

40(1)

g >

20

°0 20 40 60 80 100 Valve Position, 0/0

characteristic, flow An indefinite term encompassing characteristic, inherent floZU and characteristic, installed jlozu. [ANSI / ISA­75.05.01-2000]

characteristic, inherent-flow The relation­ship between the flow rate through a valve and the travel of the closure member as the closure member is moved from the closed position to rated travel with constant pres­sure drop across the valve. [ANSI/ISA­75.05.01-2000]

TRIM CHARACTERISTICS

QUICK OPEN

Yo FLOW

EQ %

% STEM

characteristic, inherent-flo'lv

characteristic, installed-flow The relation­ship between the flow rate through a valve and the travel of the closure member as the closure member is moved from the closed position to rated travel when the pressure drop across the valve varies under the influ­ence of the system in which the valve is installed. [ANSI/ISA-75.05.01-2000]

characteristic, linear-flow An inherent flow characteristic that can be represented by a straight line on a rectangular plot of flow

coefficient (Cv) versus percentage of rated travel. Therefore, equal increments of travel provide equal increments of flow coefficient (Cr ) at constant pressure drop. [ANSI/ISA­75.05.01-2000]

characteristic, modified parabolic flow An inherent flow characteristic that provides fine throttling action at low valve plug travel and an approximately linear characteristic for upper portions of valve travel. It is approximately midway between linear and equal percentage. [ANSI/ISA-75.05.01-2000]

characteristic, quiCk-opening flow An inher­ent flo\v characteristic in which there is a maximum flo\;v with minimum travel [ANSI/ISA-75.05.01-2000]

characteristic curve 1. A graph (curve) that shows the ideal values at steady state. Also, the output variable of a system as a function of an input variable, assuming that the other input variables are maintained at specified constant values. Note: When the other input variables are treated as parameters, a set of characteristic curves is obtained. [ANSI/ISA­51.1-1979 (RI993)] 2. Of a photographic or radiographic film, the graph of the relative transmittance of the emulsion versus expo­Sllre, or a graph of functions of these two quantities. Also known as "characteristic emulsion curve."

characteristic function A polynomial that characterizes the transient response of a sys­tem and is the denominator of the system's overall transfer function. .I

characteristic impedance The impedance ter­mination of an (approximately) uniform transmission line that minimizes reflections from the end of that line.

characterized cam A component in a valve positioner used to relate the closure member position to the control signal. [ANSI/ISA­75.05.01-2000]

characterized sleeve A part added to a plug valve to provide various flow characteristics [ANSI/ISA-75.05.01-2000]

characterized trim Control valve trim that provides defined flow characteristics, such as equal percentage, linear, or quick opening. Usually stated in terms of Cy or Ky versus travel. [ANSI/ISA-75.05.01-2000]

character-oriented Describing a communica­tions protocol or transmission procedure that carries control information that is encoded in fields of one or more bytes.

character string A connected sequence of characters.

charge 1. A defined q~a.ntity of an explosive. 2. The starting stock loaded into a batch pro­

78�

cess. 3. The material loaded into a furnace for melting or heat treating. 4. A measure of the accumulation or depletion of electrons at any given point. 5. The amount of sllbstance loaded into a closed system, such as refriger­ant into a refrigeration system. 6. The quan­tity of excess protons (positive charge) or excess electrons (negative charge) in a physi­cal body, usually expressed in coulombs.

charge amplifier An electronic amplifier used to convert the high impedance of a piezoelectric accelerometer into low imped­ance so it can be accepted by common read­out instruments.

charge-coupled device (CCD) A circuit ele­ment that transfers information by passing a definite amount of charge rather than a volt­age or current level.

chart recorder A device for automatically plotting a dependent variable against a~ independent variable. The dependent vari­able is proportional to the input signal from a transducer. The independent variable may be proportional to a transducer signal as \-veIl, but the variable is most often time or a time-dependent variable, which can be pro­duced by controlling the rate of advance of rolled chart paper. -:

chase A vertical passage in a building that contains the pipes, wires, and ducts that pro­vide heat, ventilation, electricity, running water, drains, and other building services.

chassis 1. A frame or boxlike sheet-metal sllpport for mounting the components of an electronic device. 2. A frame for a wheeled vehicle that provides most of the stiffness and strength of the vehicle body and sup­ports the body, engine, and passenger or load compartment on the running gear.

chatter Rapid cycling on and off of a device, SllCh as a relay in control process, because of insufficient band'vvidth in the controller.

Cheaperllet An IEEE 802.3 standard for a low-cost, 10 Mbit local area network (LAN) that was compatible with the Technical Office Protocol (TOP) communications pro­tocol.

check A process of partial or complete testing of the correctness of machine operations. The existence of certain prescribed conditions within the computer, or the correctness of the results prodllced by a program. A check of any of these conditions may be made auto­matically by the equipment or may be pro­grammed to occur. Related to nlarginal check.

check, parity A check that tests whether the number of ones (or zeros) in an array of binary digits is odd or even. Synonymous

charge amplifier / checksum

with odd-even check. [ISA-RP55.1-1975 (R1983)]

check, validity A check based upon known limits or upon given information or com­puter results. For example, a calendar month will not be numbered greater than 12, and a week vvill not have more than 168 hours. [ISA-RP55.1-I975 (RI983)]

chEck bit A binary check digit; often a parity bit. Related to parity check..

check box A sm.all squar~.box that appears on a video screen display; u"Sllally within a dia­log box, and tha t is used for selecting a choice of options within some application. See also ballot box.

check digit In data transmission, one or more redundant digits appended to a machine word and used in relation to the ot11er digits in the word to d"etect errors in data transmis­sion. .

checker work .An arrangement of alternately spaced brick in a furnace that has openings through which air or gas flows.

checking A network of fine cracks in a coat­ing or at the surface of a metal part. Check­ing may appear during processing but is more often associated with service, espe­cially when it involves thermal cycling.

checkout 1. The determination of the work­ing condition of a system. 2. A test or prelim­inary operation that is intended to determine vvhether a component or system is ready for service or ready for a new phase of opera­tion. 3. A generalized term that encompasses both inspection and testing. [ISA Draft RP60.10]

checkpoint A point during a machine run at which processing is temporarily halted so a record can be made of the condition of all the variables of the machine run, such as the sta­tus of input and outpllt devices and a copy of working storage. Checkpoints are used in conjunction vvith a restart routine to mini­mize the reprocessing time occasioned by functional failures. A checkpoint may also be a particular point in a program at which pro­cessing is halted for checking.

check problem A problem that is used to test the operation of a computer or to test a com­puter program. If the result given by the computer does not match the known result, this indicates an error in programming or operation.

check valve A flow control device that per­mits flow in one direction and prevents flow in the opposite direction.

checksum' 1. A routine for checking the accu­racy of data transmission by dividing the data

79�

I

chemical affinity I chromaticity

into small segments, such as a disk sector, and computing a sum for each segment. 2. An entry at the end of a block of data that corre­sponds to the binary sum of all information in the block. Used in error-checking procedures to detect single-bit errors and some multiple­bit errors.

chemical affinity 1. The relative ease with which two elements or compounds react with each other to form one or more specific compounds. 2. The ability of two chemical elements to react to form a stable valence compound.

chemical analysis The determination of the principal chemical constituents.

chemical conversion coating A decorative or protective surface coating that is produced by inducing a chemical reaction between sur­face layers of a part and a specific chemical environment, such as in chromate treatment or phosphating.

chemical engineering A branch of engineer­ing that deals with the design, operation, and maintenance of plants and equipment for chemically converting raw materials into bulk chemicals, fuels, and other similar prod­ucts through chemical reaction. Such reaction is often accompanied by a change in state or in physical form.

chemical feed pipe A pipe inside a boiler drum through which chemicals for treating the boiler water are introduced.

chemical reactor A vessel, tube, pipe, or other container vvithin which a chemical reaction is made to take place. The reaction may be batch or continuous, open or closed, and can use t11ermal, catalytic, or irradiation to initiate and control the reaction.

chemical vapor deposition A semiconductor fabrication process in which material is deposited on a substrate by means of reac­tive chemicals in the vapor phase, sometimes at low pressure (well below atmospheric pressure) or sometimes plasma-enhanced (in the presence of plasma discharge).

cherry picker Any of several types of small traveling cranes, especially one that consists of an open passenger compartment at the free end of a jointed boom.

chimney A brick, metal, or concrete stack. chimney core The inner cylindrical section of

a double-wall chimney, which is separated from the outer section by an air space.

chimney lining The material that forms the inner surface of the chimney.

chip A single large-scale integrated circuit. chipping 1. Using a manual or pneumatic

chisel to remove seams, surface defects, or

excess metal from semifinished mill prod­ucts. 2. Using a hand or pneumatic hammer with chisel-shaped or pointed faces to remove rust, scale, or other deposits from metal surfaces.

choke A valve that increases suction so as to draw in an excess proportion of fuel and facilitate the starting of a cold internal com­bustion engine. See choke coil.

chok~. coil An ind~lctor that allows direct cur­rent to pass but presents relatively large impedance to ·alternating current.

choked flow A condition wherein the flow rate through a restriction does not increase when the downstream pressure is decreased at a fixed inlet pressure. [ANSI/ISA-75.05.01­2000j

choking cavitation A limiting flow condition in which vapor formation is enough to limit the rate of flo\v through the valve to some maximum vqlue. Further increases in flow rate through the valve are only possible by increasing the valve inlet pressure, because reducing downstream pressure will no longer increase flow rate. [ISA-RP75.23-1995]

chopper Any device for periodically interrupt­ing a continuous current or flux. A chopper is used to create alternating current by periodi­cally interrupting or re\'ersing a continuous source of direct current.

Christiansen filter A device for admitting monochromatic radiation to a lens SystelTI. It consists of coarse p(j'~vder of a transparent solid that is confined between parallel win­dovvs. The spaces between particles are filled with a liquid whose refractive index is the same as that of the powder for a certain wavelength. Only that wavelength is trans­mitted by the filter withollt deviation.

chromadizing Improving paint adhesion on alumi11um and its alloys by treating the sur­face with chron1ic acid.

chromate treatment Applying a solution of hexavalent chromic acid in order to produce a protective conversion coating of trivalent and hexavalent chromium compounds.

chromatic aberration The focusing of light rays of different wavelengths at different dis­tances from the lens. This is not a significant effect with a single wavelength laser source, but it can be \-vhen working at different or multiple wavelengths.

chromaticity The color quality of light, defined by the combination of its dominant Yvaveleng-'th and purity or by its chromaticity coordinates. [ISA-5.5-1985]

80�

I

chromaticity coordinate / cinder trap�

chromaticity coordinate The ratio of any of be a liquid solution of the substances or a t11e three tristimulus values of a color sample mixture of a carrier gas and the vaporized to the sum of the tristimulus values. sample. A wide variety of detection tech­

chromaticity diagram A graph of one of the niques are used, some of which can be auto­chromaticity coordinates against another.

chromatogram The pattern formed by the chromatograph output represents zones of separated elements and compounds on a strip chart. The time at which the peak appears and the area under the peak identify the cc->mponent and the concentration.

o 2 3 4 5

TIME, MIN.

Typical Chronlatograplz Trace

chromatograph An analytical instrument that uses chromatography to separate sub­stances in order to analyze them for chemical composition and concentration.

SAMPLE 'NJECTION DEVICE

PRESSUREJFLOW REGULATOR

I

I

: - -~ ;V;N - - - - - - ~;LU-M~ - - - DETECTOR

CARRIER GAS

Chronlatograplz

chromatography An instrumental procedure

I for separating components from a mixture of chemical substances. The procedure depends

I on the selective retardation and physical

I~ ~ absorption of substances by a porous bed of

sorptive media as the substances are trans­

I i ported through the bed by a moving fluid.

The sorptive bed (stationary phase) may be a solid or a liquid dispersed on a porous, inert

mated or microprocessor driven. chromel Chromium nickel alloy used in the

positive leg of type K and type E thermocou­ples. A registered trademark of Hoskins Manufacturing Company. "

chromium plating The electrodeposition on a metal surface of eit~r·~ bright, reflective ."'" coating or a hard, less reflective coating of chromium. Also known as "chrome plating" and "chromium coating."

chromizing Producing an alloyed layer on the surface of a metal by deposition and sub­seqllent diffusion of metanic chromium.

chromophore The group of atoms within a molecule that contriblltes most heavily to its light-absorption qllalities. J

chronograph An instrument used to record the time at which an event occurs or the time interval between two events.

chronotron A device for measuring the elapsed time between two events. That time is determined by measuring the position of the superimposed loci of a pair of pulses ini­tiated by the events.

CIAC Computer Incident Advisory Capabil­ity; established in 1989, this United States Department of Energy group provides com­puter security services (such as computer virus alerts) to its employees and contractors.

CIDR Classless Inter-Domain Routing; An efficient method of assigning network addresses and modifying routing tables.

CIE Computer-integrated engineering; Com­mission Internationale de l'Eclairage, inter­national standards grollp for color and illumination, the first to specify color in terms of human perception rather than just listing the ingredients needed to make a par­ticltlar device produce a given color.

CIM-AF Comptlter-integrated manufactur­ing application framework; a framework ("protocol" is too restrictive) based upon dis­tributed object-oriented technology to allow control computers to communicate with equipment in plant, and ideally to imple­n1ent manufacturing execution systems (MES).

cinder A particle of gas-borne, partially burned fuel larger than 100 microns in diam­eter.

cinder trap A dtlst collector with staggered elements in the gas passage that concentrates larger dust particles. A portion of the gas

solid. The moving fluid (n1oving phase) may passes through the elements with the con­

81 I

CIP / cladding

centrated dust into a settling chamber, where circular-chart recorder A type of recording change in direction and velocity drops out instrument in which the input signal from a the coarser particles. temperature, pressure, flow, or other trans­

CIP Clean-in-place, typically done in food/ ducer moves a pivoted pen over a circular

fI pharmaceutical processing vessels where parts are not removable.

Cipolletti weir An open-channel flow-mea­surement device similar to a rectangular weir but having sloping sides, which results in a simplified discharge equation.

CIR Committed information rate; in network communications, a traffic measurement that is the average bandwidth that is provided over a given time sample; often mistaken as the amount of bandwidth that carrier is guar­anteeing.

circle of confusion A circular image in the focal plane of an optical system, which is the image formed by that system of a distant point object.

circuit [Comm] 1. In communications, the means of two-way communications between two points made up of both send and receive channels. [Eng] 2. In engineering, any group of related electronic paths and components that electronic signals will pass to perform a specific function.

circuit analyzer A multipurpose assemBly of several instruments or instrument circuits in one housing that are to be used to measure two or more operating characteristics of an electronic circuit.

circuit breaker A device that is designed to open and close a circuit by non-automatic means but also to open the circuit automati­cally on a predetermined overload of current without injury to itself.

circuit diagram A line drawing of an elec­tronic/ electrical system that identifies con1­ponents and diagrams ho\v they are connected.

circuit-noise meter An instrument that uses frequency-weighting networks and other components to measure electronic noise in a circuit. It gives approximately equal readings for noises that produce equal levels of inter­ference.

circuit switching A method of communica­tion in which an electrical connection between calling and called stations is estab­lished when there is a demand for exclusive use of the circuit and lasts until that connec­tion is released. See also Jrlessage sluitclling and packet sluUching.

circuit-to-ground voltage The rated value of voltage with respect to earth ground. [ANSI/ ISA-82.02.01-1999 (IEC 1010-1 Mod)]

piece of chart paper, which rotates about its center at a fixed rate with time.

circularity In data processing, a warning message that the commands for two separate but interdependent cells in a program cannot proceed until a value for one of the cells is determined.

circulariy polarized"iight Light i;" which thee polarization vector rotates periodically, but does not change magnitude, describing a cir­cle. This light can also be stated as the super­position of two plane-polarized (or linearly polari~ed) lightwaves of equal magnitude, one 90~ in phase behind the other.

circular mil A wire-gauge measurement that is equal to the cross-sectional area of a wire one mil (0.001 in.) in diameter. Its actual area is 7.8540 x 10-7 in2

.

circular polatize-d wave An electromagnetic wave for vvhich the electric field vector, mag­netic field vector, or both describe a circle.

circul"ting memory In an electronic memory device, a means of delaying information combined with a means for regenerating the information and reinserting it into the delay­ing means.

circulation The movement of water and� steam within a steam-generating unit.�

circulation ratio The ratio of the water enter­ing a circuit to the steam generated vvithin tha t circui t in a uni t of time.

circulator A pipe or tllbe for passing steam or water behveen upper boiler drums, which are usually located where the best absorption (

is low. A circulator is also llsed to apply to tubes that connect headers of horizontal \vater tube boilers with drums.

CISC Complex instruction set computer; c

developed by Intel to provide the greatest number of independently fllnctioning units by llsing them to perform tasks in parallel so ~

the processor makes the most out of each tick of the clock; compare with RISC. c1

cladding [Proc] 1. In process control, the technique of covering one piece of metal with a relatively thick layer of another metal and bonding them together. The bond may ct be produced by corolling or coextrusion at high temperature and pressure, or by explO­sive bonding. [Comm] 2. In communications,

Ithe low refractive index material that sur­ i

rounds the core of a fiber and protects CI against surface contaminant scattering.

82

I

•

cladding mode / Class H power classification, DC

cladding mode In fiber optics, the mode con­fined to cladding. A light ray that propagates in cladding.

cladding strippers Chemicals or devices that remove the cladding from an optical fiber so as to expose the light-carrying core. The term is sometimes be misapplied to chemicals or devices that remove the protective coating that is applied over cladding to protect the fiber from environmental stress.

clamping circuit A circuit that maintai11s . either the maximum or minimum amplitude

level of a waveform at a specific potential. clamping device An element of a cable entry

that prevents tension or torsion in the cable from being transmitted to the connections. [ISA-12.00.01-1999 (IEC 60079-0 Mod)]

clamping voltage Predefined "sustained" volt­age, which is held by the clamp circuit at some desired level.

clamp time In power lines, the speed with which the surge protector responds to block power surge.

clasp A nonthreaded fastener, usually hook-like and with a releasable catch.

class [Eng] 1. In engineering, a convenient jroUnd number for designating allowable pressure/temperature ratings for valves and pipe fittings using arbitrary class numbers from tables developed by the American Soci­ety for Mechanical Engineers (ASME) and the International Standards Organization (ISO) for a variety of materials. [ANSI/ISA­7.5.0.5.01-2000] [Comp] 2. In computing, a set of objects that share a common data structure and a common behavior. [ISA-TR.50.02, Part 9-2000]

class A amplifier An amplifier in which the grid bias and alternating grid voltages are stlch that plate current always flows in a specified tube.

class AB amplifier An amplifier in which the grid bias and alternating grid voltages are such that plate current in a specified tube flows considerably more than one-half of the electrical cycle but less than the entire cycle.

class A power classification, AC Voltage tol­erance is specified as the percentage devia­tion of rms voltage from nominal. [ISA-71.02-1991]

class B amplifier An amplifier in which the grid bias is approximately equal to the cutoff value, therefore making the plate current in a specified tube approximately zero when the grid voltage is zero.

Class B power classification, AC Frequency deviation is specified as the percentage devi­

ation of frequency from nominal. [ISA-71.02­1991]

class C amplifier An amplifier in which the grid bias is considerably more negative than the zero plate current value.

Class C power classification, AC Harmonic content is specified as the present rms volt­age not occurring at the primary frequency [ISA-71.02-1991]

Parameter Class ; .' '. Range

2 . 3

Voltage A -15'1'0 -20"/0 TBS tolerance to to

lO(~o +15'!c)

Frequency B ::;±0.2% ::;±1.0% ~±S.O% TBS N.A. deviation

Harmonic C ::;2'1;' ::;5% ~10"'" ::;20% TB.5 content

PhaSt' angle D ::;1° ::;2° ::;5° T.BS N.A. departure

Voltage s1"" ::;2~/" SS'),jJ TB.5 NA.

unbal.-mce

AC POlver CLassifications

Class D power classification, AC Phase angle is specified as the departure from nom­inal phase angle in degrees. This class is specified for polyphase systems only. [ISA­71.02-1991]

Class E power classification, AC Voltage unbalance is specified for polyphase systems as percentage maximum voltage deviation from the average of the phase voltage as mea­sured at the equipment terminal, divided by the same average voltage. Example: With volt­ages of 230, 238, and 225, the average is 231. The maximum deviation from the average is 7 volts, and the average unbalance =100 x (7 / 231) =3.03(Yo. [ISA-71.02-1991]

Class F power classification, DC Voltage tol­erance is specified as the percentage devia­tion from nominal voltage. [ISA-71.02-1991]

Parameter Class Range

Voltage ::;±1°j" ::;±1O% -15'%, ::;±25(;'~ T.BS

tolerance

Rlpple G s±02% ~±1.0% SIS.OW" s±15% T.BS.

CLass F Pozver Classification/ DC

Class G power classification, DC Ripple is specified in percentage terms as the ratio of the peak-to-peak value of the AC component to the nominal voltage. [ISA-71.02-1991]

Class H power classification, DC Ground reference is specified as the polarity of the terminal of a DC power source, if any, that is

83�

Class I, Division 1 location / Class II, Division 2 location�

connected to a ground reference, as follows: HI-Positive if the positive terminal is con­nected to a ground reference. H2-Nega­tive if the negative terminal is connected to a ground reference. H3-Floating if neither terminal is connected to a ground reference. [ISA-71.02-I991 ]

Class If Division 1 Ioeation A location (a) in vvhich ignitable concentrations of flammable gases or vapors can exist under normal oper­ating conditions, (b) in which ignitable con­centrations of such gases or vapors may exist frequently becallse of repair or maintenance operations or because of leakage, or (c) in which the breakdown or faulty operation of equipment or processes might release ignit­able concentrations of flammable gase1; or vapors and might also cause the simulta­neous failure of electrical equipment that

.. could act as a source of ignition. [ANSI/ISA­12.01.01-1999]

Class I, Division 2 location A location (a) in which volatile flammable liquids or flamma­ble gases are handled, processed, or used, but in which the liquids, vapors, or gases will normally be confined within closed contain­ers or closed systems from which th~.y can escape only in case equipment is operated abnormally, (b) in which ignitable concentra­tions of gases or vapors are normally pre­vented by positive mechanical ventilation and might become hazardous through fail­ure or abnormal operation of the ventilating equipment, or (c) that is adjacent to a Class I, Division 1 location and to which ignitable concentratjons of gases or vapors might occasionally be communicated unless this is prevented by adequate positive-pressure ventilation from a source of clean air and effective safeguards against ventilation fail­ure are provided. Electrical conduits and their associated enclosures that are separated from process fluids by a single seal or barrier are classified as a Class I, Division 2 loca tion if the outside of the conduit and enclosures is a nonhazardous (unclassified) location. [ANSI/ISA-12.01.01-1999]

classification 1. Sorting particles or objects by specific cri teria, such as size or function. 2. Separating a mixttlre into its constituents, such as by particle size or density. 3. Segre­gating units of product into various adjoin­ing categories, often by measuring charac­teristics of the individual units, thus forming a spectrllffi of quality. Also termed "grad­ing." See also area classification.

classification, area See area classification.

classification of a location The assignme .t f a rating such as Division I, Division 2, o~ 0

nonhazardous. Class. II, Divisio~ 1 locatio.n. A location (a) in

whIch combustible dust IS In the air under nor~~l operating conditions in quantities Sll.ffIcient to p.rodu~e explosive or ignitable mIxtures, (b) In whIch mechanical failure or the ~bnormal.operation of machinery or eqUIpment mIght cause such explosive or ignitable .~i~t~~es to be produced and might a~so provIde "a SO~trce of i~nition through SImultaneous (the word szmultaneous is not included in the Canadian definition) failure of e~ectric equipment, operation of protection deVIces, or from other causes, or (c) in which c6mbustible dusts of an electrically conduc­tive nature may be present in hazardous quantities. [ANSI/ISA-12.01.01-1999]

Class II, Division 2 location A location in which combustible dust is not normally in the air in quantities sufficient to produce explosive or ignitable mixtures and in which dust accumulations are normally insufficient to interfere with the normal operation of electrical equipment or other apparatus. However, in this type of location combustible dust may be suspended in the air as a result of the infrequent malfunctioning of handling or processing equipment. Likewise, combus­tible dust accumulations on" in, or in the vicinity of the electrical equipmerlt may be sufficient to interfere with the safe dissipa­tion of heat from electrical equipment Uf may be ignitable by abnormal operation or failure of electrical equipment. [ANSI/ISA-12.01.01­1999]

Class II, Division 2 location (Canada) A location in which combustible dusts are not normally in suspension in air or likely to be throvvn into suspension by the normal or abnormal operation or the failure of equip­ment or apparatus in quantities sufficient to produce explosive or ignitable mixtures. Hovvever, in these locations, (a) deposits or accumulations of dust may be sufficient to interfere with the safe dis~ipation of heat from electrica 1 equipment or apparatus, or (b) deposits or accumulations of dust on, in, or near electrical equipment may be ignited by arcs, sparks, or burnLng material from the electrical equipment. [ANSI/ISA-12.01.01­1999]

Class II, Division 2 location (United States) A location in which combustible dust is not normally in the air in quantities sufficient to produce explosive or ignit~ble mixtllres and in \vhich dust accumulatIons

84

Class III, Division 1 location / clearance fit�

are normally insufficient to interfere with the operating pressure range llsed by pneumatic� normal operation of electrical equipment or actllators and positioner-actuators. [ISA­�other apparatus. However, in these locations 71.02-1991]� combustible dust may be in suspension in Class L power classification, pneumatic� the air as a result of the infrequent malfunc­ Dew point is specified as the dew point tem­�tioning of handling or processing equipment. perature of the gas that is supplied at the� Moreover, combustible dust accumulations lowest ambient temperature and maximum� on, in, or in the vicinity of the electrical operating pressure of the pneumatic system.� equipment may be sufficient to interfere \vith clay atmometer A simple device for deter­�the safe dissipation of heat from electrical mining evaporation rate to the atmosphere.� •equipment or may be ignitable by the abnor­ It consists of a porou'S }1or.celain dish. that is mal operation or failure of electrical equip­ connected to a calibrated reservoir filled with ment. [ANSI/ISA-12.01.01-1999] distilled water.

Class III, Division 1 location A location in clean air 1. Air that is free of combustible which easily ignitable fibers or nlaterials that gases and contaminating substances. [ANSI/ produce combustible flyings are handled, ISA-12.13.01-2000J 2. Air that is free of any manufactured, or used. [ANSI/ISA-12.01.01­ substance that will adversely affect the oper­1999] ation of or cause a response from the instru­

Class III, Division 2 location A location in ment. [ANSI/ISA-92.02.01, Part 1-1998;� vvhich easily ignitable fibers are stored or ANSI/ISA-92.03.01-1998; ANSI/ISA­�

,.; handled (except in the process of manufac­ 92.04.01/ Part 1-1996; ISA-92.06.01-1998]� ture). [ANSI/ISA-12.01.01-1999] cleanout door A door that is positioned so that�

Class III location A location that is hazard­ accumulated refuse··may be removed from a� ous because of the presence of easily ignit- boiler setting.�

•� able fibers or flyings but in which such fibers clean room A room in which elaborate pre­�01 flyings are not likely to be suspended in cautions are employed to reduce dust parti­�the air in quantities sufficient to prodllce cles and other contaminants in the air, as� ignitable mixtures. [ANSI/ISA-12.01.01­ required for the manufacture or assembly of� 1999] delicate components or equipment.�

Class II location A location that is hazardous cleanup 1. Removing small amounts of stock because of the presence of combustible dust. by an imprecise machining operation, prima­�

t [ANSI/ISA-12.01.01-1999] rily in order to improve surface smoothness,� ·~,Class I location A location in which flamma­ t1atness, or appearal1ce. 2. The time required�

ble gases or vapors are or may be present in for an electronic leak-testing instrument to the air in quantities sufficient to produce reduce its output signal to 37 percent of the ignitable mixtures. [ANSI/ISA-12.01.01­ initial signal transmitted when tracer gas is 1999] first detected. 3. The gradual disappearance

Class Jpower classification, pneumatic of internal gases during the operation of a� Instrument pressure is specified as the oper­ discharge tube.� ating pressure range that is used by transmit­ clear To erase the contents of a storage device� ters and controllers. [ISA-71.02-1991] by replacing the contents with blanks or�

zeros. Clarified by erase. Parameter Class� Range clearance 1. The lineal distance between two

1 2 3 adjacent parts that do not touch. 2. An unob­Instru- J 130 to 150 217 to 265 1.85. structed space for inserting tools or removing� ment pre~- (18.9 to 21.8) (31.5 to 38.4)� parts during maintenance or repair. 3. The sure, kP

shortest distance in the air between two con­(ib/in. 2)�

K 130 to 300 550 to 1050 1.S.5. ductive parts. Note: This distance applies� Control (18.9 to 43.5) (79.8 to only to parts that are exposed to the atmo­�element 152.3)� sphere and not to parts that are covered with pressure,

solid insulation or casting compound.kP (ib/in. 2)

L lO"C less than !\:.A [ANSI/ISA-12.01.01-1999; ANSI/ISA­minimum ambient 1.85.Dew point� 12.16.01-1998; ANSI/ISA-82.02.01-1999]

temperature clearance distance The shortest distance Class JPOlver Classification, Pneu J1zatic measured in air betvveen condllctive parts.

clearance fit A type of mechanical fit in k Class K power classification, pneumatic which the tolerance envelopes for mating

c~~, Control element pressure is specifieci as the ~: I,

85�

clearance flow / closed loop

parts always results in clearance when the parts are assembled.

clearance flow That flow lying below the minimum controllable flow with the closure member not seated. [ANSI/ISA-75.05.01­2000] The closllre member not seated. [ANSI/ISA-75.05.01-2000]

clear-to-send (CTS) A modem interface sig­nal, defined by the V.S. standard EIA-RS­232-C, that indicates to data terminal equip­ment that it may begin data transmission.

cleaver A device that is used to cut or break optical fibers in a precise vvay so that the ends can be connected with low loss.

clevis A V-shaped metal fitting that has holes at the open ends of the legs so a pin or bolt can be inserted in order to make a closed link for attaching or suspending a load.

client One of usually several devices on a computer network that are being supplied by another processor, vvhich acts as a server of data, memory, or function(s). Client software requests and receives these functions from server software. See server.

client/server architecture An approach to computer processing in which the functions of an application are shared between multi­ple computers on the same network. Such architecture distributes the computing load among several computers on the network.

clinched The bending of the excess length of a nail so that the sharp, protruding point is forced back into the nailed material. [ISA­RP60.11-1991 ]

clinical thermometer A thermometer for accurately determining the temperature of the human body. ~10st often, it is a merclIry­in-glass maximum thermometer.

clinker A hard, compact, congealed mass of fused furnace refuse, usually slag.

clinometer A divided-circle instrument for deternlining the angle between mutually inclined surfaces.

clip (as nOlIn) In video development, a piece of video footage.

clipboard In data processing, an area in which information can be stored so that it can be "pasted" into another application.

clipping circuit 1. A circuit that prevents the peak amplitude of a signal from exceeding some specific level. 2. A circuit that elimi­nates the tail of a signal pulse after some spe­cific time. 3. A circuit element in a pulse amplifier that reduces the pulse amplitude at frequencies that are less than some specific value.

clock (eLK) 1. A master timing device that is used to provide the basic sequencing pulses

for the operation of a synchronous computer. 2. Sources for the timing signals used in syn­chronous transmission. 3. A register that automatically records the progress of real time, or perhaps some approximation to it, and records the number of operations per­formed. In addition, a register whose con­tents are available to a computer program. 4. A timing pulse that coincides with or is phase related to the occurrence of an event, such as bit rate or frame rate.

clock, real-time·· . A~.clock that indicates the passage of actual time, in contrast to a ficti­tious time set up by the computer program. Examples include the elapsed time in the flight of a missile, wherein a 60-second tra­jectory is computed in 200 actual millisec­onds or a O.I:'·second interval is integrated in 100 actual microseconds. [ISA-RP55.1-1975 (R1983)]

clock frequency The master frequency of periodic pllises that schedules the operation of the computer.

clock mode A system circuit that is synchro­nized with a clock pulse, that changes states only when the pulse occurs, and that will change, state no more than once for each clock pulse.

clock pulse A synchronization signal pro­vided by a clock.

clock rate The time rate at which pulses are emitted from the clock. The clock rate deter­mines the rate at which logical arithmetic gating is performed with a synchronous computer.

clock skew A phase shift between the clock inplits of devices in a single-clock system. The result of variations in gate delays and stray capacitance in a circuit. [ISA-RP55.1­1975 (R1983)]

clone In data processing, an exact duplication of another computer device or software.

closed circuit 1. Any device or operation in vvhich all or part of the output is returned to the inlet for further processing. 2. A type of television system that does not involve broadcast transmission, but rather transmis­sion by cable, telephone lines, or a similar method.

closed-fireroom system A forced draft sys­tem in which combustion air is supplied by elevating the air pressure in the fireroom.

closed loop 1. A combination of control units in vvhich the process variable is measured and compared with the desired value (or set point). Any deviation from the set point is fed back into the control system in such a way as to reduce deviation. Usually called

86

closed loop control/closure member types�

feedback control. 2. A hydraulic or pneu­matic system in which flow is recirculated following the power cycle. The system con­tains a limited amount of fluid, which is con­tinually reused. 3. Pertaining to a system with feedback type of control, such that the Olltput is used to modify the input. 4. An operation by which a CODlputer applies con­trol action directly to the process without manual intervention. 5. A signal path that includes a forward path, a feedback signal, and a summary point, and forms a closed cir­

, cuit. See loop, closed. (losed loop control In process control, any , system in which part of the output is fed

back to the input in order to effect regulatory action and in which the controlled quantity is measured and compared with a standard that represents the desired value or perfor­mance. See closed loop.

B =MEASURED VARIABLE C =HEAT

R+ E =DIFF~RENCE VALUE G =CONTROLLER OR PROCESS

- 8 H =FEEDBACK ELEMENT (SERVO) (HEATER) R =TEMPERATURE SEnlNG

TE =TEMPERATURE ELEMENT TI =THERMOCOUPLE TRANSMlTIER

(TEtTT)

closed-loop gain See gain, closed-loop. closed-loop numerical control A type of

numerical control system in vvllich position feedback, and often velocity feedback as well, is llsed to control the dynamic behavior and successive positions of machine slides or equivalent machine members.

closed-loop system A system that has a feed­back type of control, such that the output is used to modify the input.

closed position A position that is zero per­cent closed. [ANSI/ISA-5.2-1976 (R1992)]

close-grained Consisting of fine, closely spaced particles or crystals.

closeness in control Total variation from the desired set point of a system. Expressed as "closeness of control is ±2°C" or "system bandwidth of 4°C." Also referred to as "amplitude of deviation."

close-tolerance forging Hot forging in vvhich draft angles, forging tolerances, and cleaI1up allowances are considerably smaller than those used for commercial-grade forgings.

closing plate A plate used to cover or close openings in nonpressure parts.

closing pressure In a safety relief valve, the� static inlet pressure at the point where t11e� disk has zero lift off the seat.�

closure component The movable part of the� valve, which is positioned in the flow path to� modify the rate of flow through the valve.� [ANSI/ISA-75.05.01-2000]�

closure component, characterized A closure� component with contoured surface, such as� the "vee plug," !n order to provide various� flow characteristics.· '..� t

. closure compoilenl, cyliri~ical A cylindri­cal closure component that has a flow pas­sage through it (or a partial cylinder).

closure component, eccentric A closure COln­

ponen.t f~c~ tha~ i~f\o~ concentric with the shaft .centelJ.t~ 'al)t:f:~O'Ves into seat when

. closing. .. ~ ,,~~:'i~ •.. closure component, eccentric spherical�

disk A disk that is a spherical segment, not� concentric with the disk shaft.�

closure component, linear · A closure con).F'G>·~·"" ~~:~~~,.,~..: . nent that moves in a line perpendicular to . the seating plane.

closure component, rotary A closure compo­�nent that is rotated into or away from a seat� to modulate flow.� .I

closure component, tapered A closure com­�ponent that is tapered and may be lifted from� seating surface before rotating to close or� open.�

closure member A movable part of the valve� that is positioned in the floyv path so as to� modify or modulate the rate of flow through� the valve. [ANSI/ISA-75.05.01-2000]�

closure member configurations 1. Character­�ized: A closllre member with a contoured� surface, such as the "vee plug," in order to� provide desired flow characteristics. 2. Cylin­�drical: A cylindrical closure member that has� a flow passage through it (or a partial cylin­�der). 3. Eccentric rotary plug: The closure� member face of a rotary motion valve that is� not concentric with the shaft centerline and� moves into seat vvhen closing. 4. Eccentric� spherical disk: The disk is a spherical seg­�ment in a rotary motion valve that is not con­�centric with the disk shaft and moves into� the seat vvhen closing. 5. Linear: A closure� member that moves in a line perpendicular� to the seating plane. 6. Rotary: A closure� member that is rotated into or away from a� seat so as to modulate flow. 7. Tapered: A clo­�sure member that is tapered and may be� lifted from the seating surface before rotating� to close or open. [ANSI/ISA-75.05.01-2000]�

closure member types Ball, disk, gate, plug.

87�

cloud chamber / COBOL

cloud chamber An enclosure filled with supersaturated vapor that can indicate the paths of energetic particles when vapor con­denses along the trail of ionized molecules that are created as the particle passes through the enclosure.

clusec A llnit of power that is used to express the pumping power of a vacuum pump. It equals about 1.333 x 10-6 watt, or the po\ver associated with a leak rate of 10 mllsec at a pressure of 1 millitorr.

cluster A collection of multiple devices tl1at are connected to a central site over a single line.

CLUT Color lookup table; used by video dis­play station to define its color palette to use an 8-bit or lower digital image file.

clutch A machine element that a11o\vs a shaft in an equipment drive to be connected and disconnected from the power train, espe­cially while the shaft is running.

clutter Unwanted signals caused by noise (EMI, RFI). Also, unvvanted images on a video screen, such as shapes and messages that become unrecognizable because of zooming.

CLV Constant linear velocity of rotation, as found vvith compact disks; a formatted ,. LV-ROM.

CMAC Cerebellar Model Articulation Con­trol; technique used in neural networks.

CMM Color n1atching method; scheme for determining the best color approximations in a color management system.

CMOS Complementary metal-oxide semiconductor; uses very low power; less heat to be dissipated.

CMR(R) Common mode rejection (ratio); (measure of) ability of a device to cast off power line interference.

CMYK Cyan, magenta, yellow, black; model or color space used to convey color informa­tion; combining differing amounts of these subtractive secondary colors produces all the colors in color space. Used by most printers, CMYK vvorks by starting with all light wa\res (white paper) and then subtracting quantities of cyan, magenta, yellow, and black wave­lengths with pigments (theoretically, a maxi­mum of CMY produces black, but inks are not pure so the llsual result is a muddy brown, hence the addition of black); conlpare vvith RGB.

CNC Compllter numerical control; allovvs the control of motion in an accurate and pro­grammable man.ner through the use of a dedicated computer within the numerical control unit, with the capability for local data

input such that machine tools are freed from the need for hardwired controllers.

CNMA Communications Network for Manufacturing Applications; "sibling" of MAP in Europe that includes IEEE 802.3 and X.25 in the set of reference standards.

coalescence A term used to describe the bonding of materials into one continuous body, \vith or vvithout melting along the bond line, as in \velding or diffllsion bond­ing. _ . · " .

coal gas· Gas formed" by the destructive distil­la tion of coal.

Coanda effect A phenomenon of fluid attach­ment to one \vall in the presence of t\;VO walls.

coarse grained 1. Having a coarse texture. 2. Having a grain size, in metals, larger than about ASTM No.5.

coarse vacuum AI1 absolute pressure between abou.t 1 and 760 torr.

coating A contihtltius film of some material on a surface.

coating (fiber optic) A layer of plastic or other material applied over the cladding of an optical fiber to prevent environmental degradation and to simplify handling.

coating (optics) A thin layer or layers applied to the surface of an optical component to enhance or suppress tl1e reflection of light andlor to filter out certain wavelengths.

coaxial Having coincident axes, for exan1ple, as in a cable where a central insulated con­ductor is surrounded by one or more metallic sheaths that act as ground leads or secondary conductors.

coaxial cable A popular transmission mediuTI1 that is formed from t\\'o or more coaxial cylindrical conl~ Llctors that are insu­lated from each other. The outermost con­ductor is llsually grollnded and encased in either wire mesh or extruded metal sheath­ing. Coaxial cable is frequently used for tele­vision and radio signals as well as digital signals because its design is less likely to cause or be affected by external fields. Many varieties are available, depending upon tl1e shielding needed and the voltages/frequen­cies to be accummodated.

coaxial thermocouple element A thermoele­ment in wire forn1 within a thermoelement in tube form and electrically insulated from the tube except at the measllring junction

COBOL (Common Business Oriented Language) A specific programming lan­guage by which business data-processing pro­cedures may be precisely described in a standard form. The language is intended not

88

I

cock / coherent scattering

only as a means for directly presenting any coding sheet A fill-in form on \vhich com­business program to any suitable computer, puter programming instructions are written. for which a compiler exists, but also as a way coefficient A constant that is to be multiplied of communicating such procedures between by a variable. In digital signal processing individuals. It is primarily known for its business applications. Highly strllctured but vvordy, COBOL is "English-like" and intrinsi­cally self-documenting.

cock A valve or other mechanism that starts, stops, or regulates the flow of liquid, espe­cially into or out of a tank or other large-vol­ume container.

code 1. A system of symbols for meaningful communication. Related to instruction. 2. A system of symbols for representing data or instructions in a computer or a tabulating machine. 3. To translate the program for the solution of a problen1 on a given computer into a sequence of machine language, assem­bly language, or pseudo instructions and addresses that is acceptable to that computer. Related to encode. 4. A machine language progran1..

code, Hollerith A widely used system for encoding alphanumeric information onto cards. Hence, Hollerith cards are synony­mous with "punch cards." [ISA-RP55.1-1975 (R1983)] ,­

codec 1. A device that consists of an encoder (which translates an analog signal into a digi­tal code) and a decoder (which performs the reverse operation). 2. A compression/decom­pression algorithm. Any of several unique methods for emulating data from digital video (compression) and then redisplaying it with data substituted or assumed from the original (decompression). The term origi­nated during the 19505 for the process of dig­itizing voice signals for transmission over analog telephone lines and trunks using pulse code modulation (PC~1). The disk drive industry uses the similar term ENDEC. See [JCM,

code of practice A document that describes basic safety features and methods of protec­tion and that recommends, for example, the selection, installation, inspection, and main­tenance procedures that should be followed to ensure the safe use of electrical apparatus. [ANSI/ISA-12.01.01-1999]

codes In PCM telemetry, the manner in V\,hich ones and zeros in each binary number are denoted.

coding The ordered list, in computer code or pseudo code, of the successive computer instructions that represent successive com­puter operations for solving a specific prob­lem.

(DSP), the vallles of the coefficients in the fil­ter determine the bandpass band and stop­band characteristics.

coefficient, flow A constant (C,J, related to the geometry of a valve, for a given valve opening. Used to predict flow rate. [ANSI/ ISA-75.05.01-200Q] "",Y •

coefficient, rated flb~ . 'The flow coefficient (Cu) of the valve at rated travel. [ANSI/ISA­75.05.01-2000]

coefficient, relative flow The ratio of the flow coefficient (C ,) at a stated travel to the zflow coefficient (C ,) at rated travel. [ANSI/zISA-75.05.01-2000]

coefficient, temperature/pressure See operat­ing influence. [ANSI/ISA-51.1-1979 (R1993)]

coefficient, valve recovery See liquid pressure recovery factor. [ANSI/ISA-75.05.01-2000]

coefficient of discharge The ratio of actual tlow to theoretical flow. It includes the effects of jet contraction and turbulence.

coercimeter An in.strun1.ent for measuring the magnetic intensity of a magnet or electro­magnet.

coextrusion 1. A process for bonding two metal or plastic materials by forcing them simultaneously through the same extrusion die. 2. The bimetallic or bonded plastics shape produced by such a process.

COFF Common Object File Format; file for­mat within UNIX.

cofferdam An earthwork or piling structure that prevents water from filling an excava­tion or keeps it from surrounding and under­n1ining a pier or foundation. 2. A raised projection surrounding a hatch or trapdoor to keep \vater out of the opening.

cog A tooth on the edge of a vvheel. cogwheel A wheel with radial teetl1 on its

rim. coherence A property of electromagnetic

waves that are all the same wavelengths and precisely in phase with each other.

coherence length The distance over vvhich light from a laser retains its coherence after it emerges from the laser.

coherent fiber bundle A bundle of optical fibers that have input and output ends in the same spatial relationship to each other, thus allovving them to transmit an image.

coherent scattering Scattering of electromag­netic or particulate rays in whic11 definite phase relationships exist between the inci­dent and scattered waves. Coherent waves

89

coil/collimate

scattered from two or more scattering centers are capable of interfering with each other.

coil Any discrete and logical result that can be transmitted as output by a programmable controller.

coil breaks Creases or ridges in a metal sheet or strip that appear as parallel lines across the direction of rolling and that generally extend the full width of the material.

coil spring A flexible, elastic member in a hetical or spiral shape that stores mechanical energy or provides a pulling or restl'aining force that is directly related to the amount of elastic deflection.

COIN COS OSI Information Network; allovvs the coexistence of the OSI and TCP lIP proto­cols.

coincidence The existence of two phenomena or the occurrence of tvvo events simulta­neously in tin'le, space, or both.

coke The solid residue that.remains after most of the volatile constituents have been driven out by the heating of a carbonaceous material such as coal, pitch, or petroleum res­idues. Coke consists chiefly of coherent, cel­lular carbon with some minerals and a small amount of undistilled volatiles.

coke oven gas Gas that is produced by- the destructive distillation of bituminous coal in closed chambers. It has a heating vahle of 500-550 Btulcu ft.

cold drawing The action of pulling rod, tub­ing, or wire through one or more dies that reduce its cross section, \vithout applying heat either before or during reduction.

cold-finished Referring to a primary-mill metal product, such as strip, bar, tubing, or wire, whose final shaping operation was per­formed cold. Cold-finished material has more precise dimensions, and usually higher tensile and yield strength, than a comparable shape whose final shaping operation was performed hot.

cold joint In soldering, making a soldered connection withollt adequate heating, so that the solder does not flow to fill the spaces but merely makes a mechanical bond. A cold joint typically exhibits poor to nonexistent electrical conduction across the joint, is not leak tight, and may break loose under vibra­tion or other mechanical forces.

cold junction See reference junction. cold plate A mounting plate for electronic

components that has tubing or internal pas­sages through which liquid is circlllated to

I ; remove the heat generated by the electronic

components during operation. Also known as "liquid-cooled dissipator."

....1 ~1

cold rolling The process of rolling metal at about room temperature. The cold-rolling process reduces thickness, increases tensile and yield strengths, improves fatigue resis­tance, and produces a smooth, lustrous, or semilustrous finish.

cold trap A length of tubing between a vac­uum system and a diffusion pump or instru­ment that is cooled by liqllid nitrogen to heIR remove condensable vapors.

cold treatment. th~. ~llbzero treatment of a metal part~usualiy'at -65°F, -lOO°F, or liq­uid-nitrogen temperature-to induce metal­lurgical changes that either stabilize dimensions, complete a phase transforma­tion, or condition the metal and rrepare it for further processing.

cold working Any plastic deformation of a metal carried out below its recrystallization temperature. The cold-working process always induces strain hardening to a degree that is directly related to the percentage reduction in cross section.

cold working pressure The maximum pres­sure rating of a valve or fitting coincident with ambient temperature, generally in the range of -290 C to +380 C (-200 F to +1000 F). [ANSI/ ISA-75.05.01-2000]

collar A rigid, ring-shaped machine element that is forced onto or clamped around a shaft or similar member to restrict axial motion, provide a locating surface, or cover an open­ing.

collating sequence In data processing, the order of the ASCII numeric codes for the characters.

collator 1. A mechanical device at the output of a printing machine or copier that sorts multiple-page documents and arranges them into sets. 2. In data processing, a device for combining sets of data cards or other infor­mation-bearing elements into a desired sequence. 3. In data processing using elec­tronic files, a program or routine that is used to merge two or more files into a single, ordered output file.

collector 1. Any of a class of instruments for determining electrical potential at a point in the atmosphere, and ultimately the atmo­spheric electric field. All collectors consist of a device for rapidly bringing a conductor to the potential of the surrollnding air and an electrometer for measuring its potential with respect to the earth. 2. A device that is used for removing gas-borne solids from flue gas. 3. One of the functional regions in a transis­tor.

collimate To make parallel.

90

I

collimation I combination square

collimation The process of producing a beam of light or other electromagnetic radiation whose rays are essentially parallel.

collimator An optical system that focuses a beam of light so all the rays form a parallel beam.

collision [Sci] 1. A close approach of two or lllore bodies (including energetic particles), \vhich results in an interc11ange of energy, momentllffi, or charge. See also elastic collision and inelastic collision. [Comrn] 2. In communi­cations, the event when electrical signals from two Ilet\'vork devices in a carrier sense multiple access/ collision detection (CSMA/ CD) media access system rlin into each other. Retransmission by each is triggered but at different times so a second collision is unlikely.

collision domain In digital communications, a single carrier sense multiple access/ colli­sion detection (CSMA/CD) network that may consist of two or more media-access control (MAC) sublayers. MAC sublayers separated by repeater are within the same collision domain. MAC sublayers separated by bridge are within different collision domains. Splitting the hub or repeater i~~o

separate or multiple collision domains is often incorrectly referred to as segnzentation.

colloid 1. A dispersion of particles of one phase in a second phase, where the particles are so small that surface phenomena playa dominant role in their chemical behavior. Typical colloids include mists or aerosols (a liqUid-dispersed phase in gaseous dispersion medium), smoke (solid in gas), foam (gas in liquid), emulsions (liquid in liquid), suspen­sions (solid in liquid), solid foam such as pumice (gas ill solid), and solid solution such as colloidal gold in glass (solid in solid). 2. A finely divided organic substance that tends to inhibit the formation of dense scale and results in the deposition of sludge, or causes it to remain in suspension, so that it may be blown from the boiler.

Colmonoy A series of high-nickel alloys (manufactured by Wall-Colmonoy Corp.) that are used for the hard facing of surfaces subject to erosion.

color code 1. Any system of colors that is used to identify a specific type or class of objects from other, similar objects, for exam­ple, to differentiate steel bars of different grades in a warehollse. 2. A system of colors that is used to identify different piping sys­tems from each other in a factory or other building-for example, red for fire protec­

tion, yellow for hazardous chemical, blue for potable ,vater, and green for compressed air.

color coding The use of different background and foreground colors to symbolically repre­sent processes and process equipment attributes, such as status, quality, magnitude, identification, configuration, and so on. [ISA­5.5-1985]

color depth In video development, color depth refers to the number of bits of data used to define. the p·ixe1s' color (8 bits = 256 colors, 16 bits =65,53S'co}ors, 24 bits = 16.7 million colors).

color filter A filter containing a colored dye that absorbs some of the incident light and transmits the remainder.

colorimeter An instrument for measuring color in the same way that the eye sees color.

colorimetry Any analytical process that uses the absorption of selected bands of visible light, or sometimes ultraviolet radiation, to determine a chemical property. Examples include the end point of a reaction or the con­centration of a substance whose color indi­cates pro~uct purity or uniformity.

color mapping In digital graphics display, the process of assigning colors to the presented image by referencing a color palette.

column A vertical structural men1ber of sub­stantiallength designed to bear axial com­pressive loads.

COM Computer Output Microfilm; Compo­nent Object Model, in computing, a conl1ec­tion mechanism and protocol used to link different applications in the object linking and embedding (OLE) environment. Allo\vs the development of independent, interopera­ble software objects. De facto object standard by Microsoft competing with CORBA.

coma A lens aberration in which light rays from an off-axis source passing through the center of a lens arrive at the image plane at different distances from the axis than do rays from the same source passing through the edges of the lens.

combination automatic controller A type of control system arrangement in which multi ­ple control loops are cOllpled through pri ­mary feedback or through any of the controller elements.

combination scale An instrument scale that consists of two or more concentric or colinear scales, each graduated in eqllivalent values with two or more units of measure.

combination square A measuring and rough layout tool that consists of a special head and a short steel rule, which, when used together, can check angles of both 90° and 45°.

91

I

combination tester / command language

combination tester A tester that provides cir­ the generation of heat and povver from burn­cuitry that is capable of performing both in­ ing fuels. circuit and functional board tests. combustion control Usually, control of a

combustible The heat-producing constituent combustion process that is used as a heat of a fuel, flue gas, or fly ash. [ISA-77.41-1992]

combustible dust classifications 1. Group E d usts are those tha t have resistivi ties lower than 10,000 ohm-cm or that break down when subjected to 1,000 volts/cm across a bulk sample when tested in accordance with ISA-12.10-1988. 2. Group F dus~ are those

.that have resistivities between 100 ohm-cm and 100 meg-ohm-cm and that do not break down when subjected to 10,000 volts/em across the bulk sample when tested in accor­dance with ISA-12.10-1988. This group includes the carbonaceous dusts, which are generally regarded as semiconductors3. Group G dusts are those that have resistivi­ties greater than 100 meg-ohm-cm and that do not break down when subjected to 10,000 volts/ cm across the bulk san'lple vvhen tested in accordance with ISA-12.10-1988. This group includes the agricultural and plastic dusts, which are generally regarded as insu­lators.

combustible dust layer Any surface accumu­lation of combustible dust that is large enough to propagate ft:me or that will degrade and ignite. [ISA-12.10-1988}

combustible dusts Dusts that (when mixed yvith air in certain proportions) can be ignited and that will propagate flame. [ISA­12.10-1988]

combustible gas Any flammable or combus­tible gas or vapor that can, in sufficient con­centration by volume in air, become the fuel for an explosion or fire. Not considered com­bustible gases are materials that cannot pro­duce sufficient gas or vapor to form a flammable mixture at ambient or operating temperatures and mists that are formed by the mechanical atomization of combustible liquidsidered to be combustible gases. [ANSI/ISA-12.13.01-2000]

combustible loss The loss that represents the unliberated thermal energy that is occa­sioned by the failure to completely oxidize some of the combustible matter in the fuel.

combustion The rapid chemical combination of oxygen with the combustible elen1ents of a fuel, resulting in the production of heat. [ISA-77.41-1992]

combustion air Air that is supplied to a fur­nace or boiler either by natural or forced draft. [ISA-77.41-1992]

combustion chamber Any chamber or enclo­sure that is designed to confine and control

source. The usual manipulated variables are fuel rate and air rate. Controls are designed to supply the required heat while minimiz­ing costs and maintaining safe conditions.

combustion engine An energy conversion machine that operates by converting heat from the burning of a fuel into motion.

combustion (flam.e)isafeguard A system for sensing the presence or absence of flame and indicating, alarming, or initiating control action.

combustion rate The quantity of fuel that is fired per unit of time, as pounds of coal per

· hour or Cllbic feet of gas per minute. combustion safety control programming

type A combustion safety control that pro­vides for variolls operations at definite peri­ods of time in predetermined sequences. [ISA-77.41-1992]

come-along 1. A lever-operated chain or wire-rope hoist for lifting or pulling a: any angle. It has a reversible ratchet in the handle to permit short strokes for tensioning or relaxing the fall. Also known as a "puller." 2. A device for gripping and applying tension to a length of cable, wire rope, or chain by means of jaws that close when the user pulls on a ring.

com file A computer file name ending in .com, short for "command" file, which n10st often contains a machine code program.

comfort curve A line on the graph of dry-bulb temperature versus wet-bulb tem­perature or relative humidity. It represents optimum comfort for an average person who is not engaged in physical activity.

comfort zone The respective ranges of indoor temperature, relative humidity, and ventila­tion rate (air-movement rate) that most per­sons consider acceptable for their normal degree of physical activity and mode of dress.

command 1. An electronic pulse, signal, or set of signals to start, stop, or continue some operation. It is incorrect to use cornrnand as a synonym for instruction. 2. The portion of an instruction word that specifies the operatio11 to be performed. [ISA-RP55.1-1975 (R1983)] 3. A signal that causes a computer to start, stop, or continue a specific operation.

command language A source language that consists primarily of procedural operations, each of which is capable of invoking a func­tion to be executed.

92

I

command resolution / common storage

command resolution The maximum change common mode rejection (CMR) 1. The abil­in the value of a command signal that can be ity of a circuit to discriminate against a com­made \vithout inducing a change in the con­ mon n10de voltage. Note: It may be trolled variable. [ISA-RP55.1-1975 (RI983)] expressed as a dimensionless ratio, a scalar

comment An expression that explains or identifies a particular step in a routine, but has no effect on the operation of the com­puter performing the instructions for the routine.

commercial quality angle or channel Hot­formed carbon steel, stainless steel, or extruded aluminum shapes that are gener­ally available as standard material.

committed capability The portion of a plant's production capability that is currently in use or is scheduled for use. [ISA-95.00.01-2000]

common A reference within a system that has the same electrical potential throughout. Usually connected to ground at one point. Often different con1mons are used through­out a system, such as power comn10n, signal common, and so on depending on the accu­racy to which the reference is held.

Common Applications Service Elements (CASE) One of the application protocols specified by Manufacturing Auton1ation Pro­

1 tocol (MAP). ~ommon area A sectjon in memory that is set j aside for common use by many separate pro­

grams or modules. ­common carrier A company that furnishes

communications services to the general pub­lic. The term originated in the transportation industry, but has been expanded fron1 the movement of goods and passengers to include signals.

common cause failure The result of a com­mon cause fault. [ANSI/ISA-84.01-1996]

common cause fault A single source that will calIse failure in multiple elements of a sys­tem. The single source may be either internal or external to the system. [ANSI/ISA-84.01­1996]

common field A field that can be accessed by two or more independent routines.

common machine language In data process­ing, coded information that is in a form com­mon to a related gruup of data-processing machines.

common mode In analog data, an interfering voltage from both sides of a differential input pair (in common) to ground.

common mode interference A forn1 of inter­ference that appears between the terminals of any measuring circuit and ground. See conI/non mode voltage. See also inte~ference,

cornnlon mode.

ratio, or in decibels as 20 times the 10g1o of that ratio. [ANSI/ISA-51.1-1979 (RI993)] See voltage, conlmon 'node. 2. The ability of a meter to eliminate the effect of AC or DC noise between signal and grouI1d. Normally expressed in dB and DC or 60 Hz. One type is specified between-SIC- LO and PWR CND. In differential meters, CMR~s specified between SIC LO and ANA ~CND (meter ground).

common mode rejection ratio 1. The ability of an instrument to reject irlterference from common voltage at its input terminals \vith relation to ground (versus normal mode). See normal mode rejection ratio. CMR ratio is lisually expressed in decibels (dB). 2. A mea­sure of the ability of a detector to damp out the effect of a common-mode-generated interference voltage. Usually expressed in decibels.

common mode voltage (CMV) 1. In-phase, equal-amplitude sig11als that are applied to both inputs of a differential amplifier, usu­ally referred to as a "guard shield" or "chas­sis ground." See voltage, common mode. 2. The AC or DC voltage that is tolerable between signal and ground. One type of CMV is specified between SIC LO and PWR GND. In differential meters, CMV is speci­fied between SIC HI or LO dnd ANA GND (meter ground).

common object request broker architecture (CORBA) An approach to creating open, object- oriented system architectures. CORBA specifies the interoperability of Object Request Brokers (ORBs). This emerg­ing object-oriented programming standard \vas planI1ed by eleven companies, including IBM, Hevvlett-Packard, and Sunsoft, and is being presented by Object Management Group (OMG). CORBA competes with the de facto object standard COM, by Microsoft.

common port The port of a three-way valve that connects to the other two flow paths. [ANSI/ISA-75.05.01-2000]

common resource A resource that can pro­vide services to more than one requester. Note: Common resources are identified as either exclusive-use resources or shared-use resources. [ANSI/ISA-88.01-1995]

common storage A section of memory in cer­tain cOlnputers that is reserved for the tem­porary storage of program outputs, to be llsed as input for other programs.

93

I

compatibility interface I compiler

with the functioning of other devices on the compensating loop In thermal measure­network. These devices require unique, pur­ ments that use a resistance temperature pose-built applications in order to function detector (RTD), the lead-wire resistance com­together in a distributed application. Replac­ pensation for this type of element. An extra ing a device with a similar one of different length of vvire is run from the instrument to manufacture reqllires the redesign of part or the RTD and back to instrument, with no all of the purpose-built application, if the dis­ connection through the RTD. See resistance tributed application is to operate as it did telllperatllre detector. before the replacement. Note: Compatible compensation 1. Providing a supplemental

.devices have resources, data, functionality, device, circuit, or SReci~Lmaterialto counter­" . .,

• an·c{-cOmrhunications mappings that are suf­ act known source~ of error. [ISA-37.1-1975 ficiently different such that the devices can (R1982)] 2: In process instrumentation, pro­only function together in the same distrib­ viding a special construction or a supple­uted application network with a purpose­ mental device, circuit, or special materials so bllilt custom application. The purpose-built a$ to counteract sources of error caused by application must accommodate differences variations in specified conditions. [ANSI/ in communications protocols and services, ISA-51.1-1979 (R1993)] data formats and parameter definitions, and compensation signals In telemetry, a set of functionality between associated compatible reference sigDals recorded on tape along vvith devices. The purpose-built application often the data and used:.during playback to auto­must be designed to avoid both communica­ matically compensate for any nonllnifor!11ity tions and fllnctional interference with and in tape speed. between the associated compatible devices, compensator 1. A device that converts a sig­as well as with any other compatible devices nal into some function of it that, either alone sharing the network in other distributed or in combination with other signals, directs

bapplications. [IEC 611804] the final controlling ~lement to reduce devia­compatibility interface A point at which tions in the directly controlled variable.

hardware, logic, and signal levels are defined [ANSI/ISA-51.1-1979 (R1993)] 2. A device to allow the interconnection of indepen- .'. introduced into a feedback control system to dently designed and manufactured compo­ improve performance and achieve stability. nents. compensatory leads An arrangement of con­

compatible Can coexist with rules of rec­ necting elements between an instrument and ognized standard, but may not be compliant. a transducer or other observation device (See con1pliant.) For example, a specification­ such that variations in the properties of any compatible device will operate on a standard of the connecting elements--like temperature communications system and communicate effects that induce changes in resistance-are with other devices on that system that were compensated so that they do not affect made by same vendor and will not interfere instrument accuracy. with devices made by other vendors on that compile 1. A computer function that trans­same system. But it will not necessarily be lates symbolic language into machine lan­able to communicate \vith those other guage. 2. To prepare a machine-language devices. program from a computer program written

compensated pendulum A pendulum made in another programming language by mak­of two materials that have different coeffi­ ing use of the overall logic and structure of cients of linear expansion, and so con­ the program or by generating more than one structed that the distance between the center machine instruction for each symbolic state­of oscillation and the point of suspension ment, or both. A compile also includes per­remains the same over the normal range of forming of the function of an assembler. ambient temperatures. compiler 1. A program that translates a

compensated range The range of values high-level source language (such as FOR­within \vhich all tolerances specified for TRAN IV or BASIC) into a machine language zero, sensitivity, and so on are applicable. suitable for a particular machine. 2. A com­

compensated temperature range The specific puter program n10re powerful than an limits of temperature within which compe11­ assembler. In addition to its translating func­sation ensures that an instrument vvill oper­ tion, which is generally the same process as ate and maintain its performance to within tllat used in an assembler, a compiler is able specifications. to replace certain items of input with a series

of instrllctions, usually called subroutines.

95

I

compile time I compound angle�

ThllS, an assen1bler translates item for item complex tone A sound wave that is produced and produces as output the same number of by combining simple sinusoidal component instructions or constants that were put into waves of different frequencies. it. A compiler will do more than this. The compliance The reciprocal of stiffness. program that results from compiling is a translated and expanded version of the origi­nal. Synonymous with 1/ compiling routine" and related to 1/ assembler."

compile time The time it takes for a source program to be translated into an object pro­gram.

compiling routine Same l1s conzpiler. complement 1. A quantity expressed to the

base n, which is derived from a given quan­tity by a particular rule. Frequently used to represent the negative of the given quantity. 2. A complement on n, which is obtained by sllbtracting each digit of the given quantity from n - I, adding unity to the least signifi­cant digit and performing all resultant car­ries. For example, the twos .complement of binary 11010 is 00110. The tens complement of decimal 456 is 544. 3. A complement on n ­I, obtained by subtracting each digit of the given quantity from n - 1. For example, the ones complement of binary 11010 is 00101. The nines complement of decimal 456 is 543.

complementary metal oxide semiconductor (CMOS) 1. One type of computer semicon­ductor memory. The main feature of CMOS memory is its low power consumption. 2. A type of semiconductor device that is not spe­cifically memory.

complementary operator The logic operator that is the NOT of a given logic operator.

complementary wavelength The ll10nochro­matic wavelength of light that matches a standard reference light when combined with the sample color in suitable proportions as applied to colorimetry.

complete combustion The complete oxida­tion of all the combustible constituents of a fuel.

complete contraction A combination of both end and bottom contractions in a weir.

completion network In a strain gauge signal conditioner, the one to three resistors that must be added to make a four-arm bridge (the transducer being the active arm or arms).

complex frequency A complex number that is used to characterize exponential or damped sinusoidal waves in the same vvay as an ordinary frequency is used to charac­terize a simple harmonic wave.

complex lens A lens system that consists of more than one optical element.

(ANSI/ISA-51.1-1979 (R1993)] compliant Conforms exactly with the rules of

a recognized standard (versus conzpatible). For example, a specification-conzpliant device will operate on a standard communication system and con1J11u!licate with all other devic·es·on.that 5ySt~in made by any other vendor who'is similarly compliant.

component RGB video In video develop­ment, red, green, blue, and luminance signals are processed as separate signals (or compo­nents), thus achieving higher quality. Com­ponent RGB video is generally found in professional-grade equipment. See cornposite video.

compo~ite A material or structure that is rna-de' ~p of physically distinct components, which are mechanically, adhesively, or metal­lurgically bonded together. Examples incillde filled plastics, laminates, fila­ment-wound structures, cermets, and adhe­sive-boncied honeycomb-sandwich structures.

composite joint A connection between two parts that involves both mechanical joining and welding or brazing, and where both con­tribu te to total joint strength.

composite link Circuit-carrying frequency, time division, or statistically multiplexed data.

composite subcarrier Two or more subcarri­ers that are combined in a frequency-division multiplexing (FDM) schen1e.

composite video In video development, a video signal that combines chrominance (col­ors red- green-blue) and luminance (bright­ness of black, white, and gray) information into one signal, \vhich is relayed on a single waveform or over a single wire. Used by most consumer-grade products.

composite wave filter A selective transducer that is made up of two or more filters. The fil­ters are any combination of high-pass, low-pass, band-pass, or band-elimination types.

composition analysis An analytical process for determining the elements or compounlis that are in the sample being analyzed.

compound In object-oriented computer pro­gramming (OOP), conzpound means "consist­ing of a combination of elementary objects."

compound angle The surface contour formed by two intersecting mitered angles.

96�

i

I

compound engine / computer

compound engine A multicylinder engine in such a way as to be Llnder predominantly which the working fluid-steam, air, or hot compressive stress. gas-expands successively as it passes from compression ratio 1. In an internal combus­one cylinder to another through the engine. tion engine, the ratio of cylinder volume with

compound lever A device consisting of two or more levers, where force or motion is transferred from the arm of one lever to the next lever in the train.

compounds Thermosetting, thermoplastic, epoxy resin (cold curing), and elastometric .materials with or without fillers and/or additives after they have solidified. [ANSI/

. ISA-12.23.01-1998] compound screw A screw that has threads of

different pitches or opposite helixes on oppo­site ends of the shank.

compound semiconductor A semiconductor such as gallium arsenide that is made up of two or more materials, in contrast to simple single-element materials such as silicon and germanium.

compressibility Volumetric strain per unit change in hydrostatic pressure.

compressibility factor (Z) A factor that is used to compensate for deviation from the laws of perfect gases. If the gas laws are used to compute the specific weight of a gas, the

,I'~ computed value must be adjusted by the compressibility factor Z to obtain the true specific weight.

compressible Capable of being compressed. Gas and vapor are compressible flLlids.

compressible flow Fluid flow under condi­tions that cause significant changes in den­sity.

compression Any of several techniques for reducing the number of bits reqllired to rep­resent information in the storage or transmis­sion of digital data (thereby saving memory or bandwidth), and in which the original form of the information can be reconstructed. Also, called "compaction." See asymrnetrical compression, JPEG, MPEG, and symnzetrical COln pression.

compressional wave A wave in an elastic mediull1. that causes an element of the mediull1. to undergo changes in volume with­out rotating.

compression element An element of a cable entry that acts on the sealing ring to enable the latter to fulfill its function. [ISA-12.00.01­1999 (lEe 60079-0 Mod)]

compression failure Buckling, collapse, or fracture of a structural member that is loaded in compression.

compression member A beam, column, or other structural component tl1at is loaded in

the piston at bottom dead center to the vol­�ume when the piston is at top dead center. 2.� In powder metallurgy, the ratio of the vol­�ume of loose powder used to make a part to� the volume of the pressed compact.�

compression spring An elastic member, usu­ally made by bending rrtetijl \vire into a heli­cal coil, that resists aJorce- tending to compress it.

compression test A destrLlctive test for deter­mining fracture strength, yield strength, duc­tility/ and elastic modulus by progressively loading a short-column specimen in com­pression.

compressor [Eng] 1. In engineering, the device, in a weir-type or sleeve (pinch) valve, tl1at the valve stem forces against the back­side of the diaphragm or sleeve so as to cause the diaphragm or sleeve to move and seal against the internal flow passageway of the valve body. [ANSI/ISA-75.05.01-2000] 2. A ll1.achine-usually a reciprocating-piston, centrifugal, or axial-flow design-that is used to increase pressure in a gas or vapor. Also known as "compression machine." [Comp] 3. In computing, a hardware or soft­ware process for removing redundant or oth­erwise uninteresting words from a stream, thereby "compressing" the data quantity.

Compton scattering A form of interaction betvveen X-rays and loosely bound electrons in which their collision results in the deflec­tion of the radiation from its previous path, accompanied by random phase shift and a slight increase in wavelength.

computational process An instance of the execution of a segment by a processor using a data area.

computational stability The degree to which a computational process remains valid when subjected to effects such as errors, mistakes, or malfunctions.

computer 1. A data processor that can per­form substantial computation, including numerous arithmetic or logic operations, without intervention by a human operator during the run. 2. A device that is capable of solving problems by accepting data, per­forming described operations on the data, and supplying the results of these opera­tions. Various types of computers are calcula­tors/ digital computers, and analog computers. See analog COl1zputer, digital com­

97�

computer, notebook / computer program�

puter, general-purpose conzputer, hybrid COln­puter, and stored progran1 cOlnputer.

computer, notebook A small, portable com­puter with a flip-up screen.

computer-aided drafting or design (CAD) The technique of using computers to auto­mate the production of technical line draw­il1gS such as P&IDs.

computer-aided repair (CAR) The technique of using computers to automate the repair of electronic products after a fault has been detected.

computer-aided test (CAT) The technique of using computers to automate the test process of a device, board, or system.

Computer and Automated Systems Associa­tion of the Society of Manufacturing Engi­neers (CASAISME) A professional engineering association dedicated to the advancement of engineering technology. CASA/SME supports the administrative functions of the MAP/TOP users group.

computer code A machine code for a specific computer.

computer control Computer control is a device in which control and/or display actions are generated for use by other system devices. When used with other control " devices on the communication link, the com­puter normally performs or functions in a hierarchical relationship to the other control devices.

computer control system A system in which all control action takes place within the con­trol computer. Single or redundant comput­ers may be ltsed. [ISA-5.5-1985]

computer-dependent language A relative term for a programming language whose translation can be achieved only by a specific model (or models) of COlllputer.

computer graphics A general term identify­ing pictures or diagrams, as distinct from let­ters and numbers, presented on a computer video screen or hard copy device.

computer-independent language A lan­guage in which computer programs can be created without regard for the actual com­puters that \vill be used to process them. Related to transportability.

computer instruction A machine instruction for a specific computer.

computer-integrated engineering (CIE) An engineering environment that combines fea­tures of test and measurement, computer­aided design, manufacturing, and engineer­ing.

computer-integrated manufacturing (elM) The application of computer and comn1uni­

cations technology to automate and integrate manufacturing processes.

computer interface Serves as the interface device between the host computer and other devices on the data highway. It converts data from the protocol of the computer to that of the highway, and vice versa.

computer interface device (CID) Hardware that allows a general-purpose computer to share data with the rest of the distributed control system:" .

computerized composition An all-inclusive term for the use of computers to automati­cally perform the functions of hyphenation, justification, and page formatting.

computer-limited Pertaining to a situation in which the time required for computation exceeds the time available.

computer maintel1ance management system (CMMS) A general classification of com­puter programs that are designed to assist in managing the maintenance of process plants and other facilities. CMNIS programs also provide the history and futltre work schedul­ing of assets, including tracking preventative maintenance sche9ules for these assets. Sophisticated CMMS systems keep an inven­tory of spare parts on line with work orders and handle inventory control, automatic pur­chasing, receiving, and physical counting as well as providing personnel with the information to make appropriate decisions based on costs and operating efficiencies. See preventative lnaintenance, predictive nlainte­nance, and total productive 111aintenance.

computer network A complex that consists of two or more interconnected compllting units.

computer networking The interconnection of two or more geographically separated com­puters so that information can be exchanged between them, usually under the direction of individual, autonomOllS control programs. See also distributed processing.

computer operator A person who performs standard system operations such as adjust­ing system operation parameters at the sys­tem console, loading a tape transport, placing cards in a card reader, and removing listings from the line printer.

computer part-programming In numerical control, the preparation of a part program in order to obtain a machine program using the compllter and the appropriate processor and post processor.

computer program A series of instructions or statements in a form that is acceptable to a

98�

I

computer simulation / condensed type�

computer prepared to achieve a certain sion medium. See lnultiplexor. 2. In twisted­result. pair Ethernet networks, a multiport repeater

computer simulation A logical-mathemati­ that has diagnostic and administrative capa­cal representation of a simulation concept, bilities (often referred to as "hub" or system, or operation programmed to be solved on an al1alog or digital computer.

computer telephony Broad term for the many combinations of (PC) computers and telephones for new and unique applications.

computer word A sequence of bits or charac­ters treated as a unit and capable of being stored in one computer location. Synony­mous with lnachine (oord.

computing device A device or function that performs one or more calculations or logic operations, or both, and transn1its one or more resultant output signals. A computing device is sometimes called a computing relay. See computing relay. [ANSI/ISA-5.1­1984 (R1992)]

computing instrument See illstrlJ1nent, con1­puting.

computing relay 1. A transducer that per­forms a computational function in order to convert the input signal into the desired out­put value. 2. A device that performs one or ~more calculations or logical functions or both, and sends out one or more resultant signals.

concatenate To combine several files into one file or several strings of characters into one string by appending one file or string after another.

concave Describing a surface whose central region is depressed with respect to a flat plane that passes approximately through its periphery.

concave curve A change in the angle of incli­nation of a belt conveyor \vhere the center of the curve is above the conveyor. [ISA­RP74.01-1984]

concentrate 1. To separate metal-bearing minerals from the gangue in an ore. 2. The enriched product resulting from an ore-sepa­ration process. 3. An enriched substance that must be diluted, usually with water, before it is used.

concentration 1. The weight of solids con­tained in a unit weight of boiler water or feedwater. 2. The number of times that the dissolved solids have increased from the original amount in the feedwater to the amount in the boiler "vater because of evapo­ration in generating steam.

concentrator 1. Any communication device that allows a shared transmission medium to accommodate more data sources than there are channels available within that transmis­

99

"repeater"). concentricity The quality of two or more geo­

metric shapes that have the san1e center. Usually, the term is applied to plane shapes or cross sections of solid shapes tl1at are approximately, circular.

concentric orifice plate. A fluid-meter oriffce plate that has a circular qpening vvhose cen­ter coincides with the axis Df the center of the pipe it is installed in.

concrete A mixture of aggregate, water, and a binder, usually portland cement, that cures as it dries and becomes rock hard.

concurrent engineering Structuring the design process so that all concerned parties, including manufacturing, sales, and custom­ers, are involved from the beginning so as to bring about a more meaningful result faster.

concurrent processing Two (or il1.0re) com­puter operations that appear to be processed simultaneously when in fact the CPU is rap­idly switching between them.

condensate 1. The liq.uid product of a con­densing cycle. Also known as "condensate liquid." 2. A light hydrocarbon mixture that is formed by expanding and coolirlg gas in a gas-recycling plant so as to produce a liquid output.

condensate pot A section of pipe (4 inches in diameter) tha t is installed horizon tally at the orifice flange union in order to provide a large-area surge surface. This makes possible the movement of the impulse line fluid with the instrument element position change, reducing measurement error from the 11ydro­static head difference in the impulse lines.

condensate trap 1. A device that separates saturated water from steam in a pipe or piece of process eqllipment. 2. A device that is llsed to trap and retain condensate in a mea­surement impulse line in order to prevent hot vapors from reaching the instrument.

condensation-type hygrometer Any of sev­eral designs of dew point instruments that operate by detecting the equilibrium temper­ature at which dewar frost forms on a ther­moelectrically, mechanically, or chemically cooled surface. Surface condensation may be detected by optical, electrical, or nuclear techniques.

condensed type In the typographical compo­sition of screen displays and printing, a slen­der or narrow typeface.

I

condenser / conductivity-type moisture sensor�

condenser The heat exchanger, located at tl1e conduct electricity. Thus, conductance is top of the column, that condenses overhead reciprocal of resi;tance. vapors. For distillation, the common con­ conducting polymer A plastics material that denser cooling media are water, air, and has an electrical conductivity approaching refrigerants such as propane. The condenser rnay be partial or total. In a partial condenser, only part of the vapors are condensed, with the remainder usually being withdrawn as a vapor product.

condenser backpressure elements A multiple breakdown diffuser, normally installed in the steam condenser neck, that is used to gener­ate- a positive back pressure upstream of the condenser vacuum and to reduce the kine­matic energy of steam from an external source other than the turbine exhaust. [ANSI/ISA-77.13.01-1999]

condenser boiler A boiler in which steam is generated by the condensation of a vapor.

conditional branch See conditiollal transfer. conditional jump See conditional transfer. conditional probability The probability that

a second event will be B if the first event is A, expressed as P(B/A).

conditional stability 1. A linear system is conditionally stable if it is stable for a certain interval of values of the open-loop gain and unstable for certain lower and higher values. 2. The property of a controlled process by which it can function in either a stable or unstable mode, depending on the conditions imposed.

conditional transfer An instrllction that, if a specified condition or set of conditions is sat­isfied, is interpreted as an unconditional transfer. If the condi tions are not satisfied, the instruction causes the computer to pro­ceed in its normal seqllence of control. A con­ditional transfer also includes the testing of the condition. Synonymous with "condi­tional jump" and "conditional branch" and related to branch.

conditioning [Con1m] 1. The addition of equipment to a voice grade line, llsually by a common carrier, to provide the minimum line characteristic values required for some data transmission. 2. Modification of a signal in one form or media to match that of another, such as preparing digital output for voice-grade channel transmission, or trans­forming a 4-20mA nonlinear transmitter sig­nal into a linear digital signal \vithin the controller.

condition monitoring system A system designed to monitor the condition of a machine or process.

conductance� In conductivity measurement, a measure of the ability of a ~olution (fluid) to

that of metals. conduction Transmission of energy, thermal

or electrical, by a mediulTI that does not involve n10vement of the medillm itself.

conduction band In semiconductors, the range of energies in ~hich free electrons are allowed. See vale1'~te band a11d band (<sap.

conduction error The error in a temperature transducer as a result of heat conduction between the sensing element and the mount­ing of the transducer. [ISA-37.1-1975]

conduction pump A device for pumping a conductive liquid, such as a liquid metal, by passing an electric current across the stream of liquid and applying a magnetic field at right angles to the electrical current.

conductive dust A dust whose resistivity is less than 100 ohm-em or that breaks down when 1,000 volts per em are applied across the bulk sample when it is tested in accor­dance witl1 methods outlined in ISA-12.10­1988. Such dust is denoted as Group E in the National Electrical Code.

conductive el~stomer An elastomeric mate­rial that conducts electricity. Usually made by mixing povvdered metal into a silicone before it is cured.

conductively connected A part is conduc­tively connected to another part if the current betvveen the parts, vvith the equiplnent at ref­erence test conditions, exceeds the limit for leakage current. [ANSI/ISA-82.02.01-1999 (IEC 1010-1 Mod)]

conductivity 1. The amount of heat (Btu) transmitted in one hour throllgh one sqllare foot of a homogeneolls material that is 1 in. thick when there is a difference in tempera­ture of 1OF between the t\VO surfaces of the material. 2. The electrical conductance, at a specified temperature, between the opposite faces of a unit cllbe. Usually expressed as ohm-1 cm-1

.

conductivity bridge A simple four-arm AC bridge circuit in which a conductivity cell is the unknown circuit element. Electrically, the cell is equivalent to a resistance and a capaci­tance in series. Higher AC frequencies lead to lovver cell-polarization errors but intro­duce greater errors because of capacitance impedance. The latter can be reduced by using a phase-sensitive detector.

conductivity-type moisture sensor An instrument for measuring the moisture con­tent of fibrous organic materials such as

100

wood, paper, textiles, and grai11 at n10isture contents up to saturation.

conductometer An instrument that n1easures thermal conductivity, especially one that does so by compari11g the rates at w11ich dif­ferent rods conduct heat.

conductor Any material through which elec­trical current can flow.

conduit 1. Any channel, duct, pipe, or tube for transmitting fluid along a defined flow path. 2. A thin-wall pipe used to enclose wir­ing.

conduit entry A means of introducing a con­duit into an electrical apparatus so as to maintain the relevant type of protection. [ISA-12.00.01-1999 (lEe 60079-0 Mod)]

cone bearing A tapered sleeve bearing shaped like a truncated cone that runs in a correspondingly tapered bearing block.

cone-plate viscometer An instrument for routinely determining the absolute viscosity of fluids in small sample voillmes by sensing the resistance to rotation of a moving cone. This resistance is caused by the presence of the test fluid in a space between the cone and a sta tionary t1a t piate.

confidence level 1. The probability that the interval in question will include the true <t.

value of the quantity being measured. 2. In acceptance sampliI1g, the probability that accepted lots will be better than a specific value known as the rejectable quality level (RQL). A confidence level of 90 percent indi­cates that 90 out of every 100 lots accepted will have a quality that is better than the RQL. 3. In statistical work, the degree of assurance that a particular probability applies to a specific circumstance.

config.sys A basic computer file that outlines how that particular device is designed to operate.

configurable 1. A system feature that permits the basic structure and characteristics of a device or system, such as control algorithms, display formats, or input/output termina­tions, to be selected by entering keyboard commands. [ISA-5.3-l983] 2. A term applied to a device or system whose functional char­acteristics can be selected or rearranged through programming or other methods. The concept generally excludes physical (hard) rewiring as a n1eans for altering the configura­tion. [ANSl/lSA-5.l-1984 (R1992)] 3. In instrumentation, the term for a device or sys­tem whose functional characteristics can be selected or rearranged by selecting from libraries of algorithms, images, and "soft­

conductometer I conformity

vviring" techniques (generally, methods other than programming langllages).

configuration 1. The arrangement of the parts or elements of something. 2. A low-level, fill-in-the-blank form of programming a pro­cess control c!evice. 3. In computing, a particu­lar selection of hardvvare devices or software routines and/or programs that function together. 4. A term applied to a device or sys­tem whose functional.characteristics can be selected ·or reurrang~d tRrough progr~!1l-ming or other methods. 5. Th'e hardware, firmware, and/or software combinations that make up a system. 6. The selection of hardvvare devices, firmware, or software programs that fits the application tech11010gy to its particular use.

CHOICE OF OPEN NETWORK FLEXIBILITY

II� OR PROPRIETARY NEnNORK SECURITY�

1

COMPARING� CONFIGURATION APPROACHES�

ConfIguration

configure To run an installation procedure that sets up soft"vare to operate on a particu­lar computer and printer.

confined flow The flow of a continuous stream of fluid within a process vessel or conduit.

conformance The condition whereby a device conforms to the manufacturer's speci­fications. See accuracy and error band.

conformance testing Running a standard set of tests to determine whether some product meets a set of standards and/or specifica­tions. Testing does not gllarantee that prod­ucts can interoperate, only that they conform to specification.

conformity Of a curve, the closeness to which it approximates a specified Cllrve (e.g., loga­rithmic, parabolic, cllbic, etc.). Note: 1. Con­formitv is usually measured in terms of nonco~formitya~nd expressed as conformity, for example, the maximllffi deviation bet\veen an average curve and a specified curve. The average curve is determined after making two or more full range traverses in each direction. The value of conformity is referred to the output unless otherwise stated. 2. As a performaI1ce specification,

101�

I

conformity, independent I connector�

conformity sholtld be expressed as "indepen­ in a circular path such that it forms a cone. dent conformity," "terminal-based confor­ The antenna is steered automatically so that mity," or "zero-based conformity." When the telemetry source is kept at the center of expressed simply as conformity, it is the cone. assumed to be independent conformity. See linearity" [ANSI/ISA-51.1-1979 (RI993)]

conformity, independent The maximum deviation of the calibration curve (the aver­age of llpscale and downscale readings) from a specified characteristic curve positioned so as to minimize the maxi111um deviation. [ANSI/ISA-51.1-1979 (R1993)] .

conformity, terminal-based The maximum deviation of the calibration curve (the aver­age of upscale and downscale readings) from a specified characteristic curve positioned so as to coincide with the actual characteristic curve at upper and lower range values. [ANSI/ISA-51.1-1979 (RI993)]

conformity, zero-based The maximllffi devia­tion of the calibration curve (the average of llpscale and downscale readings) from a specified characteristic curve positioned so as to coincide with the actual characteristic curve at the lower range vallIe. [ANSI/ISA-51.1-1979 (RI993)]

OUTPUT

ACTUAL CALIBRATION CURVE (AVERAGE OF UPSCALE AND DOWNSCALE READINGS)

SPECIFIED CHARACTERISTIC CURVE

/

.// ./�

/� / MAXIMUM ± DEVIATIONS ARE

I MINIMIZED AND EQUAL

LOWER RANGE­VALUE

INPUT

I....-----SPAN----~~I o 100%

Zero-based COl1forrnity

conforms Agrees fully with the rules of a recognized standard, is corrlpliant. See corn­pliant and cOl1zpatible.

conical orifice An orifice that has a 45° bevel on the inlet edge to yield a more constant and predictable discharge coefficient at low­flow velocity (Reynolds nlIm_ber less than 10,000).

conical scan antenna An alitomatic-tracking antenna system in which the beam is driven

coniscope See koniscope. conjugate bridge An arrangement of electri­

calor electronic components in which the supply circuit and detector circuit are inter­changed as compared with the normal arrangement for that type of bridge.

conjugate iml?edance~ · An impedance pair in which the magnitudes of the resistance and reactive components ot one are equal to the corresponding values of the other, but whose reactive components are of opposite signs.

connect To establish linkage between an interrupt and a designated interrupt servic­ing program. See disconnect

connecting rod Any straig11t link that trans­mits power or motion from one part of a mechanism to another; especially one that links a rotating member to a reciprocating member. An example is the link that attaches a piston to the crankshaft in a reciprocating internal combustion engine.

connection In communications, connection implies a transport link-level control circuit. See association.

connection facilities Terminals, plugs and sockets, screws, and other parts that are used to electrically connect the conductors of external circliits. [ISA-12.00.01-1999 (IEC 60079-0 Mod); ISA-12.02.01-1999 (IEC 60079­11 Mod)]

connection head An enclosure attached to the end of a thermocouple within \tvhich elec­trical connections are made.

connection head extension A threaded fit­ting or an assembly of fittings extending between the thermowell or angle fitting and the connection head. [ANSI-MC96.1]

connections, external Terminations that are intended to be connected in the field. [S12.16.01]

connections, internal Terminations that are intended to be connected in the factory under controlled conditions. [ANSI/ISA­12.16.01-1998 (lEe 60079-7 Mod)]

connector 1. A connector is a coupling device that is used to connect the wire medillffi to a fieldbus device or to another segment of wire. 2. A coupling device employed to con­nect the medium of one circuit or communi­cation element with that of another circuit or communication element. [ANSI/ISA-50.02, Part 2-1992] 3. Any detachable device for providing electrical continuity between two conductors. 4. In fiber optics, a device that

102�

I

connector insertion loss / constant voltage power supply�

joins the ends of t\VO optical fibers together high resistance, making it very suitable for temporarily. precision wire-wound resistors and for form­

connector insertion loss The power loss (in ing thermocouples with iron, copper, silver, dB) by an optical signal as it passes through a fiber-optic connector.

connect time 1. The length of time a user is connected to a computer system measured from logon to logoff. 2. The amOllnt of time it takes a switching network to connect the calling party to the called party.

consecutive acce-ss A method of data access that is characterized by the sequential nature of the I/O device involved. For example, a card reader is an example of a consecutive access device. Each card must be read one after another, and no distinction is made between logical sets of data in or among the cards in the input hopper.

conservation of charge The principle that states that the total charge of an isolated sys­tem is constant. Also known as ~/charge con­serva tion." .. conservation of energy (first law of therlnodynamics) The principle that energy cannot be created or destroyed, although it can be changed from one form into another. Also known as "energy conser­vation." '"

consistency A qualitative means for classify­ing substances, especially semisolids, accord­ing to their resistance to dynamic changes in shape.

console 1. A main control desk for an inte­grated assemblage of electronic equipment. Also known as "control desk." 2. A grouping of control devices, instrument indicators, recorders, and alarms that are housed in a freestanding cabinet or enclosure to create an operator's workstation. 3. The cabinet or enclosure for a floor-model radio or televi­sion receiver, or similar electronic device. 4. That part of a terminal that provides user input and output capability. 5. A control cen­ter, or part of a control center, that has one or more inclined surfaces for mounting instru­ments and controls within a range, for conve­nient viewing and manipulation

constant 1. A value that remains the same throughout the distinct operation. The oppo­site of variable. 2. A data item that takes as its value its name (hence, its value is fixed dur­ing the execution of a program).

constant-amplitude (filter) A reference to the characteristic of a butterworth filter. See But­ter'luorth.

constantan An alloy of copper (50% to 60%) and nickel that has a very low temperature coefficient of resistance and comparatively

and so on. Used as a negative lead in types E,� J, and T thermocouples.�

constant-bandwidth (CBW) The spacing of FM subcarriers equally with relation to each other. See proportional bandzuidth.

constant cavitation An early level of cavita­tion that is ~h'aracterized by mild, steady popping or crac~lin.g sounds, which may be audible or detected by·vibration measure­ments. It is the next higher inflection point on the cavitation profile above the point of incipient cavitation. This level is represented by the constant cavitation coefficient se. [ISA­RP75.23-1995]

constant-current potentiometer A type of null-balance instrument for determining an unknown DC voltage, usually less than 10 V, under conditions that maintain constant cur­rent in the detector circuit. Resolution of up to one part in 103 can be achieved with a sin­gle potentiometer slidewire and up to one part in 101 with a multidecade device.

constant-current transformer A type of transformer that automatically adjusts the output of its secondary circuit to maintain a constant current under varying load imped­ances when its primary windings are con­nected to a constant-voltage power supply.

constant-delay (filter) See bessel. constant-head meter A flow measurement

device that maintains a constant pressure dif­ferential by varying the cross section of a flow path through the meter, such as in a pis­ton meter or rotameter.

constant-load balance A single-pan weight­ing device that has a constant load and in which the sample weight is determined by hanging precision weights from a COllnter­poised beam.

constant-resistance potentiometer A type of null-balance instrument for determining an tlnknown DC voltage, usually less than 10 V, by using a constant scaling resistor in paral­lel with the potentiometer circuit.

constant status A status attribute that has both the high- and low-limit indications set and is llsed to indicate that the downstream block cannot respond to the output of the upstream block. [ISA-TR50.02, Part 9-2000]

constant voltage power supply A power supply that is capable of maintaining a fixed voltage across variable load resistance and OVt=.f defined inpllt voltage and frequency change. Output Cllrrent is auton1atically con­

103�

I

constant-volume gas thermo... / context switching multitasking�

trolled to keep constant the product of out­ or that separate to make or break electrical put current and load resistance. continu i ty.

constant-volume gas thermometer A device contact sense module A device that monitors for detecting and indicating temperature and converts program-specified groups of based on Charles's law-the pressllre of a confined gas varies directly with absolute temperature. In practical instruments, a bulb immersed in the thermal medium is con­nected to a Bourdon tube by means of a cap­illary. Changes in temperature are indicated directly by the movement of the Bourdon tube becalise of changes in bulb pressure.

constrained mechanism A mechanical device in which all members move only along predetermined paths.

constraint 1. The limit of normal opera ting range. 2. A condition imposed on a system that limits the freedom of the system. The constraint may be physical or mathematical, necessary or incidental.

consumables 1. Those materials or compo­nents that are depleted or that require peri­odic replacement through normal use of the instrument. [ANSI/ISA-92.02.01, Part 1-1998; ISA-92.03.01-1998; ANSI/ISA-92.04.01, Part 1­1996; ISA-92.06.01-1998] 2. Resources that are not normally included in bills of material or are not individually accounted LJr in specific production requests. [ISA-95.00.01-2000]

contact In hardware, a set of conductors that can be brollght into contact by electrome­chanical action and that thereby produce switching. In software, a symbolic set of points that are open or closed depending on the logic status assigned to them by internal or external conditions.

contact input See input, contact. contact inspection In ultrasonic testing, a

method for scanning a test piece tha t involves placing a search unit directly on a test piece surface that has been covered with a thin film of couplant.

contactor A mechanical or electromechanical device for repeatedly making and breaking electrical continuity between two branches of a povver circllit, thereby establishing or inter­rupting current flow.

contact output See output, contact. contact rectifier A device for converting AC

electrical power into DC power. It is con­structed of two different solids that are in contact with each other. Rectification is accomplished because the selected combi11a­tion of solids yields grea ter electrical conduc­tivi ty in one direction across the interface between them than in the other direction.

contacts The electrically conducting parts in a contactor that repeatedly come into contact

field-switch contacts into digital codes so they can be input into the computer.

contact symbology The representation of logic schemes in contact or ladder diagram form.

contact thermography A method for measur­ing surface temp~ratlirein vvhich the surface of an object is covered with a thin layer of luminescent material and then vie\ved linder ultraviolet light in a d~rkened room. The brightness that is viewed indicates the sur­face temperature.

contact-type membrane switch A disk­shaped momentary-contact switch of multi­layer construction. The active element con­sists of two condllctive buttons that are separateli by an.~nsll1atingwasher. Finger pressure on one face of the disk brings the . blittons into contact, completing the electri­cal circuit. When the pressure is released, the contacts separate, breaking the electrical cir­cuit.

contact-wear allowance The thickness that may be lost because of wear from either of a pair of mating electrical contacts before they cease to adequately perform their intended function.

contained parameter A block parameter that is accessible to the communicatlon netvvork but may not be linked to an input or output parameter. The parameter value may be usecl in the block algorithm or written by the block algorithm. [ISA-TR50.02, Part 9-2000]

container A special-purpose, reusable enclo­sure for s11ipping cargo via truck, rail, and ship. [ISA-I{IJ 60.11-1991]

contaminant That which makes something else impure or corrlipt through contact or mixing. [ISA-71.04-1985]

contaminate To make impure or corrupt by contact or mixing.

contamination The presence of an unwanted substance-usually, a substance that causes an llndesired effect or interferes wi th a desired effect.

content-addressed storage See associative storage.

Contention 1. A condition on a multidrop communication channel in which two or more locations try to transmit at the same time. 2. Unregulated bidding for a line or other device by multiple users.

context switching multitasking Multiple applications can be loaded into the com­

104

I

contiguous file / contrast

puter, but only the one in the foreground is compound's manufacturer of the compound.� given process time. This simplest level of [ANSI/ISA-12.23.01-1998 (lEe 60079-18� multitasking is the \tvay early versions of Mod)]� Microsoft Windows vvorked. That is, once an continuous operation A process that oper­�application is in the foreground, all other applications stop. Compare cooperative nlulti­tasking and tirne-slice 1111iltitasking.

contiguous file A file that consists of physi­cally adjacent blocks on a mass-storage device.

continuity test Any test to determine the presence and/ or location of broken or open connections or of shorts in printed circllit boarli interconnections, chassis, cables (including fiber optic), and harness.

continuity tester A device for testing whether a fiber-optic communication system' forms a continuous optical path between t"vo points.

continuous blowdown The uninterrupted removal of concentrated boiler water from a boiler in order to control total solids concen­tration in the renlaining water.

continuous control Automatic control in which the controlled quantity is measured continuously and corrections are a continu­ous function of the deviation.

continuous dilution The technique of sup­plying a protective gas flow continuously to an enclosure that contains an internal poten­tial source of flammable gas or vapor for the purpose of diluting any flammable gas or vapor that could be present to a level below its lower explosive limit / lower flammable limit (LEL/LFL). [ANSI/ISA-S12.01.01-1999]

continuous duty Term that describes a device that is able to operate continuously \'vith no off or rest period.

continuous-duty rating The maximum power or other operating characteristic that a specific device can sustain indefinitely vvith­out significant degradation of its functions.

continuous flow production A method of ongoing production that is typical of the pro­cess industries, as compared with batch 1rlal1­ufacturing.

continuous mixer A type of mixer in which starting ingredients are fed continuously and the final mixtllre is withdravvn continuously, without stopping or interrllpting the mixing process. Generally, unmixed ingredients are fed at one end of tIle machine and blended progressively as they move toward the ot11er end, "vhere the mixture is discharged.

continuous operating temperature of the compound The maximum temperature to which the compound can be sllbjected con­tinuously according to the data given by the

ates on the basis of continuous flow, as� opposed to batch, intermittent, or sequenced� operations.�

continuous-path numerical control A type of numerical-control system that involves not only the specification of the successive end positions of ma~hine.~1ides or equivalent machine members, but-also the automatic generation of the linear, circular, or parabolic path to be followed in moving from one end position to the next. Also known as "con­touring numerical control."

continuous rating 1~"The rating that is appli­cable to the specified operation for a speci­fied llninterrupted length of time. [ISA-37.1­1979 (R1982)] 2. A defined power input or set of operating variables that represents the maximum values for operating a device con­tinuously for an indefinite time without reducing its normal service life.

continuc:ls spectrum A distribution of wave­lengths in a beam of electromagnetic radia­tion in which the intensity varies continuously with wavelength. Further, the intensi ty exhibits no characteristic structure such as a series of bands vvhere the intensity does not abruptly change at discrete vvave­lengths. See also band spectrUlll.

continuous stirred tank reactor (CSTR) A widely used type of chemical reactor to which feed is continuously added and from which product is continuously removed. The vessel is well-stirred, so the product's com­posi tion is the same as the overall vessel composition. This type of reactor has been extensively modeled and has served as a test bed for many novel control schemes.

continuous weld A welded joint in which the fusion zone is continuous along the entire length of the joint.

contour control system A system of control in vvhich two or more controlled motions move in relation to each other so that a desired angular path or contour is generated.

contouring numerical control See continu­ous-path nunlerical control.

contraction The .narro\ving of the stream of liquid that passes throllgh a notch of a weir.

contract maintenance 1. Maintenance that is not normally done by plant personnel. 2. A maintenance service organization that con­tracts to do specific maintenance.

contrast In a photographic or radiographic image, the ability to record small differences

105�

I

contrast factor / control, velocity limiting�

in light or X-ray intensity as discernible dif­ converted, outside of any feedback loop, into ferences in photographic density. corrective action to minimize deviations of

contrast factor The slope of the central por­ the controlled variable. NOTE: The use of tion of a graph of photographic density ver­ feedforward control does not change system sus the exposure for a given photographic or radiographic en1ulsion.

control 1. Frequently, one or more of the com­ponents in any mechanism that is responsi­ble for interpreting and carrying out manually initiated directions. 2. In some applications, a mathematical check. 3. Instructions that determine conditional jumps often are referred to as "control instructions," and the time sequence of the execution of these instructions is called the "flow of control." 4. Any manual or auto­matic device for regulating a machine to keep it at normal operation. If automatic, the device is motivated by variations in tempera­ture, pressure, water level, tin1e, light, or other influences. 5. Maintaining a desired set point of steam temperature during opera­tion. [ANSI/ISA-77.44-1995]

control, adaptive Control in which automatic n1eans are used to change the type or influ­ence (or both) of control parameters in such a way as to improve the performance of the control system. [ANSI/ISA-51.1-1979 oil,

(R1993)] control, cascade Control in which the output

of one controller is the set point for another controller. [ANSI/ISA-51.1-1979 (R1993)]

control, differential gap Control in which the output of a controller remains at a maximum or minimum value until the controlled vari­able crosses a band or gap, causing the out­put to reverse. The controlled variable must then cross the gap in the opposite direction before the autput is restored to its original condition. [ANSI/ISA-51.1-1979 (R1993)]

control, direct digital Control that is per­formed by a digital device that establishes the signal to the final controlling element. [ANSI/ISA-51.1-1979 (R1993)]

control, direct multiplex A control means using hardware, a computer program, or both, to directly interleave or simultaneously receive or transmit two or more signals on a single channel. [ISi\.-RP55.1-1975 (R1983)]

control, feedback Control in which a mea­sured variable is compared to its desired value to produce an actuating error signal which is acted upon in such a way as to reduce the magnitude of the error. [ANSI/

stability because it is not part of the feedback loop which determines the stability charac­teristics. [ANSI/ISA-51.1-1979 (R1993)]

control, high-limiting Control in \vhich the output signal is prevented from exceeding a

•predetermined high limiting value.� [ANSI/ISA-51.)-1979 (R1993)]�

control, low limiting Control in which out­put signal is prevented fron1 decreasing beyond a predetermined 1000v'limiting value. [ANSI/ISA-51.1-1979 (R1993)]

control, optimizing Control that automati­cally seeks and maintains the most advanta­geous value of a specified variable, ratl1er than maintaining it at one set value. [ANSI/ISA-51.1-1979 (I{1993)]

control, relay A control system in which the error signal must r~:~h a certain value before the controller reacts to it, so that the control action is discontinuous in amplitude.

control, safety combustion See "combustion (flame) safeguard."

control, safety Control (including relays, switches, and other auxiliary equipment used in conjunction therewith to form a safety control system) which are intended to prevent unsafe operation of the controlled equipment.

control, shated time Control in which one controller divides its computation or control time among several control loops rather than by acting on all loops simultaneously. [ANSI/ISA-51.1-1979 (R1993)]

control, supervisory Control in which the control loops operate independently subject to intermittent corrective action; e.g., set point changes from an external source. [ANSI/ISA-51.1-1979 (R1993)]

control, time-proportioning Control in \vhich the output signal consists of periodic pulses whose duration is varied to relate, in some prescribed manner, the time average of the output to the actuating error signal. [ANSI/ISA-51.1-1979 (R1993)]

control, velocity limited Control in which performance is limited by the rate of change attainable by some component, usually an actuator.

control, velocity limiting Control in which the rate of change of a specified variable is

ISA-51.1-1979 (R1993)] prevented from exceeding a predetermined control, feedforward Control in which infor­ limit. [ANSI/ISA-51.1-1979 (R1993)] I

rnation concerning one or more conditions� that can disturb the controlled variable is� I

106� I

I

control accuracy / control card

control accuracy The degree to which a con­ control agent The energy or material that trolled process variable corresponds to the comprises the process element, which is con­desired value or set point. trolled by manipulating one or more of its

control action Of a controller or a controlling attributes. The attribute(s) are commonly system, the nature of the change of the out­put that is effected by the input. Note: The output may be a signal or the value of a manipulated variable. The input may be the control loop feedback sigl1al when the set point is cOl1stant, an actuating error signal, or tl1e output of another .controller. [ANSI/ISA­51.1-1979 (R1993)] See proportional control action, integral control action, and derivative control action.

control action, derivative (rate) (0) In pro­cess instrun1entation, control action in vvhich the output is proportional to the rate of change of the input. [ANSI/ISA-51.1-1979 (R1993)]

control action, floating In process instru­mentation, control action in which the rate of change of the output variable is a predeter­mined function of the input variable. Note: The rate of change may have one absolute value, several absolute values, or any value between two predetermined values. [ANSI/

~ ISA-51.1-1979 (R1993)] ~.. control action, integral (reset) (I) Control

action in which the output is proportional to the time integral of the input. That is, the rate of change of output is proportional to the input. [A·NSI/ISA-51.1-1979 (R1993)]

control action, proportional (P) Control action in which there is a continuous linear relation between the output and the input. This condition applies when both the output and input are within their normal operating ranges and when the process is operating at a frequency below a limiting value. [ANSI/ISA-51.1-1979 (R1993)]

control action, proportional-plus-derivative (rate) (PD) Control action in \vhich the out­put is proportional to a linear combi11ation of the input and the time rate of change of the input. [ANSI/ISA-51.1-1979 (R1993)]

control action, proportional-plus-integral (reset) (PI) Control action in which the out­put is proportional to the linear combination of the input and the time integral of the input. [ANSI/ISA-51.1-1979 (R1993)]

control action, proportional-plus-integral (reset)-plus-derivative (rate) (PID) Control action in vvhich the output is proportional to a linear combination of the input, the time integral of the input, and the time rate of change of the input. [ANSI/ISA-51.1-1979 (R1993)]

termed the controlled variable(s). control algorithm A matl1ematical represen­

tation of the control action to be performed. control and instrumentation engineer An

engineer \vho applies standard engineering stand~rds and p~actices to the specification,

.' . sizing, and functiohal design of instrumenta­tion hardware or control systems. Such engi­neers must have a clear understanding of the manufacturing or scientific process to be con­trolled. They serve as the key person on the instrumentation design and operation team, often supervising and reviewing the team's efforts. Under supervision, the control and instrumentation engineer participates in the design and plaJ)l1ing of control and instru­ment systems as~regi1ired by the project assignment, including: (a) collecting back­ground information, (b) preparing drawings and calculations, (c) designing or modifying systems, (d) assisting in the selection and procllrement of equipment, (e) ensuring compliance with applicable standards and codes, (f) completing assigned tasks on schedule, (g) assisting technicians and designers as needed, and (h) possibly spe­cializing in a specific engineering discipline. 3. See InstrZl111ellt Engineer.

control apparatus An assembly that contains one or more control devices to manipulate a controlled variable.

control block A storage area throllgh vvhich a partjcular type of information that is regllired for control of the operating system is communicated among its parts.

control board A panel that contains control devices, instrument indicators, and some­times recorders, which display the status of a system or subsystem and from which switches, dials, and controllers can be manip­ulated to alter system operating variables. Also knovvn as control panel and panel board.

control bus The data highvvay that is used for carrying control signals.

control calculations Installation-dependent� calculations that determine output signals� fron1 the computer in order to operate the� process plant. These mayor may not lIse� generalized equation forn1s such as rID� forms.�

control card� A card that contains input data� or parameters for a specific application of a� general routine.�

107

control center / control instruction�

control center 1. An eqllipment structure or group of structures from which a process is measured, controlled, and/or monitored. [ANSI/ISA-51.1-1979 (R1993)] 2. An equip­ment structure, or group of structures, from which a system is measured, controlled, and/or monitored. [ISA-RP 60.4-1990]

control center facility A combination of the services, protective enclosures, and environ­mental treatment that are necessary for the proper functioning of the control center. [ISA-RP 60.4-1990] Control center facilities can be found -in the following: (a) an area witl1in an enclosure that is constructed to protect a control center and its operating per­sonnel (the enclosure mig11t also contain a computer room, motor control center room, instrument/electric shop, laboratory, and personnel facilities such as toilets, lockers, and offices), (b) an unenclosed area located either indoors or outdoors at grade level or in an elevated or subsurface structure, (c) an area in a mobile unit, or (d) an area in a pre­fabricated or skid-mounted enclosllre. [ISA­RP60.1-1990]

control character A character whose purpose is to control an action rather than to pass data to a program. For instance, ASCII (·on­trol characters have an octal code between 0 and 37. The control c11aracter is normally typed by holding down the Ctrl key on a ter­minal keyboard while striking a character key.

control chart A plot of some measured qllan­tity, such as a dimension, against the sample number, time, or quantity of goods pro­duced. This plot can be used to determine a quality trend or to make adjustments in pro­cess controls as necessary to keep the mea­sured quantity within prescribed limits.

control circuit 1. A circllit in a control appa­ratus that carries the electrical signal that is used to determine the magnitude or duration of control action. It does not carry the main power that is used to energize instrumenta­tion, controllers, motors, or other control devices. 2. A circuit in a digital computer that performs any of the following functions: directing the seqllencing of program com­n1.ands, interpreting program commands, or controlling the operation of the arithmetic element aJld other computer circuits in accor­dance \vith the interpretation.

control complexity ratio (CCR) A measure of the complexity of a particular control sys­tem's logic configuratio11.

control computer A process computer that directly controls all or part of the elements in the process. See process conlputer.

control counter A physical or logical device in a computer that records the storage loca­tions of one or more instruction words, which are to be used in sequence, unless a transfer or special instrllction is encountered.

control device Any device-such as a heater, valve, electron tube, c0ntactor, pump, or actuator-that.ts ~sed to directly effect a change in some 'process attribute ..

Control Diagram Language (CODIL) A pro­cess-oriented language and system that was once offered by Leeds and Northrup Com­pany.

control domain In (the referenced) standard, control domain is synonymous with the manufacturing operations and control domain. [ISA-95.00.01-2000]

control drawing A drawing or other docu­ment that is provided by the manufacturer of the intrinsically safe or associated apparatus. It deta ils the interconnections tha tare allowed between the intrinsically safe and associated apparatuses. If the intrinsically safe or associated apparatus is investigated under the ent.ity concept, the control drawing should include the applicable electrical parameters that vvill make it possible to select the apparatus for interconnection. [ISA-12.02.01-1999 (60079-11 Mod); ANSI/ ISA-12.01.01-1999]

control electrode In an electron tube or simi­lar device, an electrode whose potential can be varied to induce variations in the current flowing between t\VO other electrodes.

control element A cOll1ponent of a control system that when stimulated by an actuating signal reacts to manipulate a process attribute.

control equipment Equipment that controls one or more output quantities to specific val­ues. Each value is determined by manual set­ting, local or remote programming, or by one or more input variables. [ISA-82.03-1988]

control function See control operation. control grid An element of an electron tllbe

that is ordinarily positioned between the anode and cathode to act as a control elec­trode.

control initiation The signal that is intro­duced into a measurement sequence to regu­late any subsequent control action as a function of the measured quantity.

control instruction A computer instruction that directs the sequence of operations.

108

control key / controller, multiple-speed floating�

control key A computer control key that, when pressed with another key, gives that key a different meaning.

control L In video development, a device control standard that is used in many con­sumer and prosumer devices. It allo~s rewind, play, and record commands to be triggered externally.

controlled cooling Cooling a part from an elevated temperature in a specific medium in

,- ortier to prodllce desired pr~perties or micro­. sttuc·ture, or to avoid cracking, distortion, or

high residual stress. The usual cooling medi­ums, in descending order of severity, are brine, water, soluble oil, fused salt, oil, fan-blown air, and still air.

controlled medium The process fluid or other sllbstance that contains the controlled variable.

controlled system The body, machine, or pro­cess that determines the relationship between an indirectly controlled variable and a corresponding directly controlled vari­able. [ANSI/ISA-51.1-1979 (R1993)] See sys­tem, controlled.

controlled variable 1. The variable that the control system attempts to keep at the set .. point value. The set point may be constant or variable. 2. The part of a process to be con­trolled (flow, level, temperature, pressure, etc.). 3. A process variable that is to be con­trolled at some desired value by manipulat­ing another process variable.

I

controller 1. A device or program that oper­ates automatically to regulate a controlled variable. Note: This term by itself is adequate for the process industries where the vvord con­troller always means "automatic controller." In some industries, "automatic" nlay not be implied, so the term alltonlatic controller" is preferred. [ANSI/ISA-51.1-1979 (R1993)] 2. A device that has an output that varies in order to regula te a controlled variable in a specified manner. A controller may be a self-contained analog or digital instrument, or it may be the equivalent of such an instrument in aI shared-control system. An automatic control­ler varies its Olltput automatically in responseJ

i� to a direct or indirect input of a measured pro­�cess variable. A manual controller is a manual loading station, and its output is not depen­dent on a measured process variable but can be varied only by manual adjustment. A con­troller may be integral with other the func­tional elements of a control loop. [ANSI/ISA­5.1-1984 (R1992)] 3. Any manual or automatic device or system of devices that is used to reg­ulate processes within defined parameters.

[ISA-77.41-1992] 4. A manual or automatic device or system of devices that is used to regulate the boiler steam temperatures within defined parameters as set forth by a turbine/boiler manufacturer. [ANSI/ISA­77.44-1995] 5. Any automatic, semiautomatic, or manual device or system of devices that is used to regltlate the boiler tllrbine, or any other equipment, vvithin defined parameters. If automatic,_ the dev~ce or system responds to variation?~irrteI11.peiature, pressure, water

··level, flow, or other control variables. [ANSI/ ISA-77.13.01-1999] 6. Any manual or auto­matic device or system df devices used for regulating boiler systems to keep the boiler at normal operation. If automatic, the device or system is motivated by variations in tem­perature, pressure, "vater level, time, flow, or other influences. [ANSI/ISA-77.42.01-1999] 7. A device for interfacing a peripheral unit or subsystem in a computer, for example, a tape controller or a disk controller. 8. A device that contains all the circuitry needed for receiving data from external devices, both analog and digital; processes the data accord­ing to preselected algorithms; and then pro­vides the results to external devices.

controller, derivative (D) A controller that produces derivative control action only. [ANSI/ISA-51.1-1979 (R1993)]

controller, direct-acting A controller in which the value of the output signal increases as the value of the input (measured variable) increases. [ANSI/ISA-51.1-1979 (R1993)] See controllerf reverse-acting.

controller, floating A controller in which the rate of change of the output is a continuous (or at least a piecevvise continuous) function of the actuating error signal. Note: The Ollt­put of the controller may remain at any value in its operating range when the actuating error signal is zero and constant. Hence, the output is said to float. When the controller has integral control action only, the mode of control has been called "proportional speed floating." It is recommended that the term integral control action be used as a replace­ment for proportional speed floating control. [ANSI/ISA-51.1-1979 (R1993)]

controller, integral (reset) (I) A controller that produces integral control action only. Note: It may also be referred to as "controller, proportional speed floating." [ANSI/ISA­51.1-1979 (R1993)]

controller, multiple-speed floating A float­i11g controller in which the OUtpllt may change at two or more rates. Each rate corre­sponds to a definite range of values of the

109�

I

controller, multiposition / controller, single-speed floating�

actuating error signal. [ANSI/ISA-51.1-1979 controller, proportional-speed floating See (R1993)] con troller, in tegral (reset) (I). [ANSI / ISA-51.1­

controller, multiposition A controller that 1979 (R1993)] has two or more discrete values of output. controller, ratio A controller that maintains a [ANSI/ISA-51.1-1979 (R1993)]

RANGE­ SWITCHING LIMIT POINTS

~

=>0­ ~ '\~

=> ~

o POSITION 1 ~

POSITION 2

.'"� POSITION 3�

POSITION 4�

POSITION 5�

'--r--A Y • • • W

RANGE­LIMIT

'\

- INPUT "'----6•

ZONE 1 ZONE 2 ZONE 3 ZONE 4 ZONE 5

controller, on-off ,A two-position controller in which one of the two discrete values is zero. [ANSI/ISA-51.1-1979 (R~993)]

controller, program A controller that auto­matically holds or changes set point in order to follow a prescribed program for a process. [ANSI/ISA-51.1-1979 (R1993)]

controller, proportional (P) A controller that produces proportional control action only. [ANSI/ISA-51.1-1979 (R1993)]

controller, proportional-plus-derivative (rate) (PD) A controller that produces propor­tional-pIus-derivative (rate) control action. [ANSI/ISA-51.1-1979 (R1993)]

controller, proportional-plus-integral (reset) (PI) A controller that produces propor­tional-pIus-integral (reset) control action. [ANSI/ISA-51.1-1979 (R1993)]

me Kc

b

Controller, Proportional-pIus-integral (Reset)

controller, proportional-pIus-integral (reset)­plus-derivative (rate) (PID) A controller that produces proportional-pIus-integral (reset)-plus-derivative (rate) control action. [ANSI/ISA-51.1-1979 (R1993)]

predetermined ratio bet\veen hvo variables. [ANSI/ISA-51.1-1979 (R1993)]

A

FRSP

B

A

FRSP

controller, ratio (a and b)

controller, reverse-acting A controller in which the value of the output signal decreases as the vallIe of the input (measured variable) increases. [ANSI/ISA-51.1-1979 (R1993)] See controller, direct-acting.

controller, sampling A controller that in order to effect control action uses intermit­tently observed values of a signal SlICh as the set point signal and the actuating error signal or the signal that represents the controlled variable. [ANSI/ISA-51.1-1979 (R1993)]

controller, self-operated (regulator) A con­troller in which all the energy to operate the final controlling element is derived from the controlled system. [ANSI/ISA-51.1-1979 (R1993)] .;

controller, single-speed floating A floating controller in \vhich the output changes at a fixed ra te that increases or decreases in accordance with the sign of the actuating error signal. See controller,floating. Note: A neutral zone of values of the actuating error

110�

I

controller, three-position I control panel�

signal in which no action occurs may be that a control variable is compared to a set used. point and returns to the process in the form

controller, three-position A multiposition of a manipulated variable. [ANSI/ISA-77.44­controller that has three discrete values of 1995] 3. A control loop is a group of function OUtptlt. Note: This three-posit!on control.is commonly achieved by selectIvely energlz­ina a multiplicity of circuits (outputs) in

I� order to establish three discrete positions of� the final controlling element.� [ANSI/ISA-51.1-1979 (R1993)]�

controller drift See drift.�

I controller file A circuit card cage in which� the control functions of several process loops� were shared by tl1e full set of cards within it.� A term that \vas more common with those� distributed control systems (DCSs) of the late� 1970s through 1980s that used this style.�

controller system A system in vvhich deliber­ate guidance or manipulation is use.d to achieve a prescribed value for a varIable. Note: It is subdivided into a cop-trolling sys­tem and a controlled system. .

controller, time schedule A controller in which the set point or the reference input sig­nal automatically adheres to a predeter­mined time schedttle. [ANSI/ISA-51.1-1979 (R1993)]

controller, two-position A multiposition con­troller that has two discrete values of output. [ANSI/ISA-51.1-1979 (R1993)]

control limit An alltomatic safety control that is responsive to changes in liquid level, pres­sure, or temperature or position for the pllr­pose of limiting the operation of the controlled equipment.

control limits In statistical quality control, the llpper and lower values of a measured quantity, which establish the range of accept­ability. If any individual measureme~tfalls outside this range, the relevant part IS

rejected, and if the sample average for the same measurement falls outside the range l

the entire lot is rejected. controlling means The components of an

automatic controller that are directly involved in producing an output control sig­nal or other controlling action.

controlling system See systenz, controlling. control logic The sequence of steps or events

that is necessary to perform a particular function. Each step or event is defined to be either a single arithmetic or a single Boolean expression.

control loop 1. Two or more devices process­ing a single variable that may provide an input signal to a c011trol system. [ANSI/ISi\­67.14.01-2000] 2. A combination of field devices and control ftlnctioI1S arranged so

blocks (FBs) that execute at a specified rate� within a fieldbus device or distribllted across� the fieldbus network. 4. A combination of� tvvo or more instruments or control functions� arranged so that signals pass from one to� another for the purpose.of measuring and / or�

. controlling a process variable. See close.d loop� and open loop.�

SP ERROR CONTROLLE~ MANIPULAJED VARIABLE CONTROLLED VARIABLEPROCESS m

SENSOR

MEASURED VARiABLE

Control Loop Block Diagram

control loop instability A regular oscillation of a feedback contra.! system, caused by excessive loop gain. It is independent of external disturbances.

control mode A specific type of control action such as proportional, integral, or derivative. [ANSI/ISA-51.1-1979 (R1993)]

control module The lo\vest-Ievel grouping of equipment in the physical model that can carrv out basic control. Note: This term applies to both the physical equipment and the equipment entity. [ANSI/ISA-88.01-1995]

control operation An actio11 performed by a single device, such as the starting or stop­ping of a particular process. Conventionally, carriage return, fault change, rewind, end of transn1issio11, and so on, are control opera­tions, whereas the actual reading and trans­mission of data are not.

control output module A device that stores commands from tl1e computer and translates them into signals that can be used for control purposes. The control output module car: generate digital outputs ~o cont~ol on-o.ft devices or to pulse set pOInt statIons, or It can generate analog output (voltage or cllrrent) so as to operate valves and other process control devices.

control panel 1. A part of a computer console that contains n1anual controls. 2. See plug­board, console and autonlatic control panel. 2. A cabinet or surface \vith any combination of instruments, such as switches, indicators, gauges, controllers, recorders, and so on,

111�

I

control point I control unit

which are mounted for easy access and ease auto-manual station. The operator interface of operation. An example are the panels in of a distributed control system may also be control rooms on \vhich are mounted instru­ regarded as a control station. [ANSI/ISA-5.1­n1.ents so operations can use them to control 1984 (R1992)] [Comm] 2. In commu.nications, a process.

control point The set point or other reference value that an automatic controller acts to maintain as the measured value of a process variable under a given set of conditions.

control precision The degree to which a given value of a controlled variable can be reproduced for sever~l independent control initiations using the same control point and the same system operating conditions.

control program 1. A group of programs that provide such functions as the handling of input/olltput operations, detecting and recovering from errors, loading programs, and communicating bet\veen the program and the operator. 2. Specific programs that control an industrial process.

control programming Writing a user pro­gram for a computer that will control a pro­cess in the sense of enabling it to react to randon1 disturbances in t~me in order to pre­vent the impairment of yield or dangerous conditions.

control recipe A type of recipe that, through its execution, defines the manufacture of a single batch of a specific product. [ANSI/ ISA-88.01-1995]

control resolution The smallest increment of change that can be induced in the controlled process variable as a result of control-system action.

control rod A long piece of neutron-absorb­ing material that fulfills one or both of the following functions: controlling the number of neutrons available for triggering nuclear fission or absorbing sufficient neutrons to stop fission in case of an emergency. Control rods are moved in and out to control reactiv­ity.

control room area See area, control roan/. control signal override device A device that

overrides the control signal to the valve actu­ator, for example, solenoid valves, lock-up valves, bypass valves, and so on. [ANSI/ ISA-75.05.01-2000]

control spring A spring designed to prodllce a torque that is equal and opposite to the torque produced by an instrument's moving element for any position of the moving ele­ment within the limits of its operating range.

control station [Cont] 1. In control, a manual loading station that also provides svvitching between the manual and automatic control modes of a control loop. It is also knovvn as an

a station on a network that supervises that network's control procedures such as poll­ing, selecting, and recovery. It is also respon­sible for establishing order on the line in the event of contention or any other abnormal situation arising betvveen any stations on that network. .

control' sub·~Ysferii· The portion of a distrib: uted control system (DCS) that directs the' • sequence of operations, interprets coded instructions, and initiates appropriate com­mands to computer functions before execut­ing process actions.

control system A systen1 in which deliberate guidance or manipulation is used to achieve a prescribed value for a variable (see ANSI/

.� ISA~51.1-1979 (R1993)). [ANSI/ISA-67.14.01­2000]

control system, automatic it COritrol system that operates without human intervention. See also control systerrl. [ANSI/ISA-51.1-1979 (R1993)]

control system, multielement (multivari­able) A control system that utilizes input signals derived from two or more process variables for tlle purpose of jointly affecting the action of the control systenl. Note 1: Examples of such systems are the input sig­nals that represent pressure and tempera­ture, or speed and flovv, and so on Note 2. A term used primarily in the power illdustry. [ANSI/ISA-51.1-1979 (R1993)]

control system, noninteracting A control system that has multiple inpllts and outputs and in vvhich any given input-output pair is operating independently of any other input­output pair. [ANSI/ISA-51.1-1979 (R1993)]

control systems engineer An engineer who designs, assembles, builds, and operates instrumentation and cOlltrol systems. He or she applies standard engineering standarlis and practices to the specification, sizing, and functional design of instrumentation hard­ware and control systems. Such engineers must have a clear understanding of the man­ufacturing or scientific process to be con­troUed. They serve as the key person on the instrumentation design and operation team, often supervising and revie\ving tIle team's efforts. See instrunlent engineer.

control unit [Meas] 1. In measurement, the portion of a multipart gas detection instrll­ment that is not directly responsive to the conlbustible gas. Rather, it responds to the

112

I I

control valve / converter

electrical signal that is obtained from one or control valve characteristic See characteristic, more detector heads to produce an indica­ inherent-flolu; characteristic, installed-flow; tion, alarm, or other output function if gas is characteristic, equal-percentage; characteris tic, present at the detector head location. [ANSI/ linear-j107.v; characteristic, nlod~fied parabolic ISA-12.13.01-2000; ANSI/ISA-92.02.01, Part 1-1998; ANSI/ISA-92.03.01-1998; ANSI/IS/\.­92.04.01/ Part 1-1996; ISA-92.06.01-1998] [Comp] 2. In computing, the portion of a computer that directs the sequence of opera­tions, interprets the coded instructions, and initiates the proper commands to the com­puter circuits preparatory to executing them. [Cant] 3. In control, a device designed to reg­ulate the fuel, air, water, or electrical supply to the controlled equipment. It may be auto­matic, semiautomatic, or manual.

control valve 1. Any valve that controls pres­sure, rate of flovv! or flow direction in a fluid- or gas-filled system. 2. A final control­ling element, through which a fluid or gas passes, that adjusts the size of a flow passage in order to modify the rate of flow of the fluid, as directed by a signal from a control­ler. [ANSI/ISA-51.1-1979 (R1993)] 3. A device, other than a common, hand-actuated on-off valve or self-actllated check valve, that directly manipulates the flow of one or more fluid process streams. Use of the term hand control valve is limited to hand-actuated valves that (a) are used for process throttling or that (b) require identification as an instru­ment. 4. A power-actuated device that modi­fies the fluid flow rate in a process control system. It consists of a valve that is con­nected to an actuator mechanism (including all related accessories) and that is capable of changing the position of a closure member in the valve in response to a signal from the controlling system. [ANSI/ISA-75.05.01­2000]

floIo; characteristic, quick-opening j1ozv. control valve gain The change in the flow rate

as a function of the change in valve travel. It is the slope of the installed flow characteris­tic curve. [ANSI/ISA-75.05.01-2000; ANSI/ ISA-51.1-1979 (R1993); ANSI/ISA-5.1-1984 (RI992)] _

control variable -I.-the variable that the con­trol system attempts to keep at the set point value. 2. The part of a process that you want to control (flow, level, temperature, pressure, etc.) 3. A process variable that is to be con­trolled at some desired value by manipulat­ing that variable or another process variable. [ANSI/ISA-51.1-1979 (R1993)]

convection 1. The transmission of heat bv cir­culating a liquid or a gas such as air. Co~vec­tion may be natural or forced. [ISA-77.41­1992] 2. Circulatory action that occurs in fluid at nonuniform temperature because of the variation of its density and action of gravity.

convection cooling Removing heat from a body by means of heat transfer, in which a moving fluid is used as the transfer medium. Convection cooling usually involves only the motion callsed bv differences in heat content between fluid ne.lar the hot surface and fluid at some distance from the surface. [ISA­77.41-1992]

convection-type superheater See superheater. convergence The condition in \vhich all the

electron beams of a multibean1 (color) cath­ode ray tube intersect at a specific point.

conversational mode Communication between a terminal and a computer in which each entry from the terminal elicits a response from the computer and vice versa.

conversion (to engineering units) Scaling signals from their raw input form to the form that is used internally, usually into floating­point engineering units.

conversion coating A protective surface layer on a metal that is created through chemical reaction bet\veen the metal and a chemical solution.

conversion time The time required by an analog-to-digital converter to perform a complete measurement.

conversion transducer Any transdllcer whose output-signal frequency is different from its input-signal frequency.

converter [Comm] 1. In commltnications, a device that receives information in one form of an instruIaent signal and transmits an out­

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I

converter, analog-to-digital (AVe) I copyfitting

put signal of another form. An instrument convolution In digital signal processing that changes a sensor's output to a standard (DSP), a mathematical process that describes signal is properly designated a transmitter, the operation of filters. In discrete convolu­not a converter. Typically, a temperature ele­ tion, the vailles of corresponding samples are ment (TE) may connect to a transmitter (TT), not to a converter (TY). A converter is also referred to as a "transdllcer." However, trans­ducer is a completely general term, and its llse specifically for signal conversion is not recommended. [ANSI/ISA-5.1-1984 (R1992)] Widely used converters include AID (analog to digital), 01 A (digital to ana­log), liP (current-to-pneumatic pressure con­verter), P /1 (pneumatic-pressure-to-cllrrent converter), P IV (pneumatic-pressure-to­voltage converter), and V IP (voltage-to­pneumatic pressure converter). [Proc] 2. In process control, a type of refining furnace in which impurities are oxidized and removed by blowing air or oxygen through the molten metal.

converter, analog-to-digital (ADC) An instrument that is used to convert analog sig­nals into digital coded values that are pro­portional to the analog input voltages. [ISA­RP55.1-1975 (R1983)]

converter, digital-to-analog (DAC) An instrument that converts digital information into analog signals that are proportional to the numerical value of the digital informa­tion. [ISA-RP55.1-1975 (R1983)]

convex A term describing a surface whose central region is raised with respect to a flat plane that passes approximately through its periphery.

convex curve A change in the angle of incli­nation of a belt conveyor such that the center of the curve is below the conveyor. [ISA­I<P74.01-1984]

convex programming In operations research, a particular case of nonlinear programming in which the function to be maximized or minimized as well as the constraints are appropriately convex or concave functions of the controllable variables. Contrast this vvith dynanlic progranlll1ing, integer progralnming, linear programnling, mathenlatical prograrn­nzing, and quadratic progranzrning.

conveyor A continuously moving materi­als-handling device for transferring large numbers of individllal items or large quanti­ties of bulk solids from one location to another over a relatively short distance along a fixed path.

conveyor stringers Support members for a conveyor on which the idlers are mounted. [ISA-RP74.01-1984]

multiplied and added together to form a new function.

coolant 1. The t1uid that is contained within the reactor coolant pressure boundary. [ISA­67.03-1982] 2. Any fluid that is used prima­rily to remove heat from an object and carry it a\vay. 3. I~ a mach-ining operation, any cut­ting fl'uid whose chief function ~s to keep' the tool and workpiece cool.

Coolidge-type x-ray tube A high-vacuum tube in which electrons emitted from a high-voltage cathode impinge on a water-cooled metal target that is inclined with respect to the tube axis. X-rays emitted from the focal spot on the target are directed through a side windovv in the metal tllbe enclosllre, where a material that is relatively transparent to X-rays-beryllium foil, mica, aluminum, or special low-absorption glass­allows them to escape.

cooling tower A tovverlike structure in which atmospheric air circulates and cools warm water, generally by direct contact (evapora­tion). Used in industry to remove heat from cooling water so that it can be used again to cool a process.

cooperative multitasking Common to the Macintosh platform, this is a step above con­text switching. Background applications are given processor time but only when the fore­grollnd task is idle and allows it, such as while waiting for a keystroke. Compare C011­

text szuitching 11111ltitasking and tinle-slice 1Jlulti­tasking.

coordination control A type of control that directs, initiates, and/or modifies the execu­tion of procedural control and the utilization of eqllipment entities. [ANSI/ISA-88.01­1995]

coprocessor A device that is added to a CPU to perform special fltnctions more efficiently than the CPU can alone. Often dedicated only to the task of processing nllmeric functions. Especially useful when using math-inten­sive programs such as spreadsheets and CAD functions.

copy In data processing, to reproduce data from one storage device to another.

copyfitting In the typographical composi­tion of screen displays and printing, the cal­culation of how much space the provided copy will use in a given screen or page; the selection of type fonts, type size, and art; the

114�

copy preparation I Coriolis-type mass flowmeter�

performance of scaling and placement; and so on

copy preparation The process of providing the directions for as well as checking illustra­tion details and placing the text and graphic elements in the design of the screen displays and page layouts.

copy protection A feature that makes it impossible to copy a disk, particularly soft­ware program disks, by adding security codes to the disk.

CORBA See conlmOl1 object request broker archi­.. tecture.

corbinotron A device that consists of a corb­ina disk, which is made of high-mobility semiconductor material, and a coil that pro­duces a magnetic field that is perpendicular to the plane of the disk.

cord-connected equipment Equipment that connects to a supply circuit receptacle by means of a permanently attached flexible power supply cord and attachment plug or by means of a detachable power supply cord. [ANSI/ISA-82.02.01-1999 (EIC 1010-1 Mod)]

core [Eng] 1. In engineering, a strongly ferro­magnetic material that is used to concentrate and direct lines of flux produced by an elec­tromagnetic coil. 2. The inner layer in a com-'" posite material or stnlcture. 3. The central portion of a case-hardened part that supports the hard outer case and gives the part its toughness and shock resistance. 4. An insert placeci in a casting mold to form a cavity, recess, or hole in the finished part. 5. A rod or closed hlbe that is inserted in a tube to reduce the flow area. [Comp]6. In computing, mag­netic memory elements that once constituted the main memory in most computer systems until they were displaced by semiconductor memory. [Comm] 7. In fiber optics, the cen­tral or inner region of the optical wavegttide through which light is transmitted along the length of the fiber. It is typically 8 to 12 microns in diameter for single-mode fiber and, 50 to 100 microns for multimode. The core has an index of refraction that is higher than that of the surrounding cladding. Light is confined to the core by a difference in the refractive index between the core and clad­ding, with the latter having a lower index.

core dump See storage dunzp. core iron A grade of soft steel that is suitable

for making the cores used in electromagnetic devices such as chokes, relays, and trans­formers.

core memory A once common type of main memory storage used in a central processing

tlnit, in which binary data are represented by switching the polarity of magnetic cores.

core resident Pertaining to programs or data that are permanently stored in core memory for fast access.

core storage See nlagnetic core. core wire Copper wire that has a steel core,

often used to make antennas. Coriolis effect An accelerating force acting

on any body that moves freely above the earth's surfa~e.du€ to.th~ fact that the earth is rotating with respect to'a given axis through its center. It is the Coriolis effect that causes, for instance, the bubble in a level carried on an airplane to be deflected perpendicular to the direction o£ flight, and a river in the Northern Hemisphere to scour its right bank more than its left bank where a river in the Southern Hemisphere scours its left bank more than its right. The Coriolis effect is the basis for many mass flowmeters.

Coriolis force A force that results from Cori­olis acceleration acting on a mass moving with a velocity radially outward in a rotating plane.

Coriolis-type mass flowmeter An instru­ment for measuring mass flow rate by deter­mining the torque caused by radial acceleration of the fluid.

INPUT FLOW

(A) SINGLE u-TUBE DESIGN

RIGHT� POSITION�

DETECTOR�

(B) DUAL U-TUBE DESIGN

Coriolis Mass Flolvmeters

115�

I

Corliss valve I corrosion�

Corliss valve A type of valve that is used to its transmission or impedance properties, or admit steam to, or exhaust it from, a recipro­ both. cating engine cylinder. correlation 1. The interdependence or associ­

comer-cube prism A prism in which three ation between two variables that are quanti­flat surfaces meet at right angles, as they would if they were the corner of the cllbe. Incident light through a planar face is reflected back to the source.

corner frequency In the asymptotic form of a Bode diagram, that frequency that is indi­cated by a break point, that is, the junction of two confluent straight lines asymptotic to the log gain curve. [ANSI/ISA-51.1-1979 (RI993)]

corner taps The differential-pressure signal location in an orifice flange union as defined by the corner that is forn1ed between the ori­fice plate and the internal diameter of the flange.

corona voltmeter A type of voltmeter that uses the inception of corona to determine the crest value of voltage in an AC electric cur­rent.

Corporation for Open Systems (COS) An organization formed i11 1985 to coordinate member company efforts in the selection of standards and protocols, conformance test­ing, and the establishment of certification.

correction In process instrumentation, the algebraic difference between the ideal vallIe and the indication of the measured signal. It is the quantity that added algebraically to the indication gives the ideal value. Note: A pos­itive correction denotes that the indication of the instrument is less than the ideal value: Correction = (Ideal Vallie) - (Indication)

correction time See tinle, settling. corrective action The change that is pro­

duced in a controlled variable in response to a control signal.

corrective maintenance 1. An activity that is not normal in the operation of a piece of equipment and that therefore requires that access be gained to its interior. Such activities are expected to be performed by qualified personnel who are aware of the hazards involved. These activities typically include locating the causes for faulty performance, replacing defective components, adjusting service controls, and the like. [ANSI/ISA­12.12.01-2000] [ANSI/ISA-RP12.6-1995] 2. Maintenance that is specifically intended to eliminate an existing fault. Synonymous with ernergency rnaintenance. Contrast "vith preventive l1zain tenance.

corrective network An electronic network that is incorporated into a circuit to improve

tative or qualitative in nature (see illustra­tion). 2. A measurement of the degree of sim­ilarity of two images as a fUl1ction of detail and the relative position of t11e images. It is obtained by multiplying the Fourier trans­forms of the t\VO images, then taking the Fourier !rans.fo~~ ?f..the product.

...". . . ~ ... '. 55 •••• I ...··..... ..� ...... .�.. ... . .. .�

40 ••• .. . __--"--'~35~ __"""""'-~ 35 +----~__+_~~_.__~

15 16 16 17 17 18 18 19 19 20 15 16 16 17 17 18 18 19 19 20

.•. ... " . . ·... . .... . . -. ....

40 •••

•35 +---- ......---.-__-----. 35 +-.-1...........-__~--+--r----1------.----.

15 16 16 17 17 18 18 19 15 16 16 17 17 18 18 19

Scatter Diagrams Sholoing� Degrees of Correlation�

correlation check A procedure \vhereby the performance and accuracy of a calibration system is checked against another calibration system llsing "master flowmeters" as the standards. [ISA-RP31.1-1997]

correlator A logic device that compares a series of bits in a data stream with a known bit sequence and puts out a signal when cor­relation is achieved. One use of the correIator is as a pulse code modulation (PCM) frame synchronizer.

cor~espondingstates A principle that states that two substances should have similar properties at corresponding conditions with reference to some basic properties. Exalnples would be critical pressure and critical tem­perature.

Corrodekote test An accelerated corrosion test for electrodeposits in which a specimen is coated with a slurry of clay in a salt solu­tion and is then exposed for a specified time in a high-humidity environn1ent.

corrosion 1. The deterioration of a substance (usually a metal) becallse of a reaction with its environnlent. [ISA-71.04-1985] 2. The wasting away of metals because of chemical

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I

corrosion fatigue / counter

action in a boiler. Usually caused by the pres­ cotter A tapered part similar to a wedge or ence of °2, CO2 or an acid. key that can be driven into a tapered hole to

corrosion fatigue A synergistic interaction of hold an assembly together the two failure mechanisms corrosion and cottered joint A joint in which power is fatigue such that cracking occurs much more rapidly than would be predicted by simply adding their separate effects. Failure by cor­rosion fatigue requires the simultaneous presence of a cyclic stress and a corrosive environn1ent.

corrosion protection Preventing corrosion or reducing the rate of corrosive attack by any of several means including coating a metal surface with a paint, electroplate, rust-pre­ventive oil, anodized coating, or conversion coating; adding a corrosion-inhibiting chemical to the environment; using a sacrifi­cial anode; or using an impressed electric current.

corrosive Any sllbstance or environment that causes corrosion.

corrosive flux A soldering flux that removes oxides from the base metal when the joint is heated in order to apply solder. The flux is usually composed of inorganic salts and acids that are corrosive and must be removed before the soldered components are placed in ..

(;; service, so as to ensure maximum service life. corrosiveness The degree to which a sub­

stance causes corrosion. corrugated fastener A thin, corrugated strip

of steel that is llsed to fasten two pieces of wood together by hamn1ering it into the wood at approximately right angles to the joint line.

corrugating Forming sheet metal into a series of alternating parallel ridges and groo\Tes. The forming may be done by rolling the metal between matched grooved rolls or by forming it in a press brake that is equipped with a special-shaped punch and die.

corrupt In data processing, the inclusion of errors in programs or data.

caSE Common Open Software Environ­ment; effort by the UNIX community to unify the various versions of UNIX.

cosmic rays Penetrating ionizing radiation whose ultimate origin is outside the earth's atmosphere. Some of the constituents of cos­mic rays can penetrate many feet of material such as rock.

COTS Commercial off-the-shelf; in reference to hardware, firmware, and/ or soft\vare that is not proprietary to one specific vendor but rather is available from any of several ven­dors in functionally identical and inter­changeable forn10

transferred across the joint via shear force� that is transverse to the longitudinal axis of a� bar (usually tapered along one side to ensure� a tight fit). This bar, known as a "cotter,"� holds the joint together.�

cotter pin A sp~i.t pin, usually formed by fold­ing a length'of half-founq wire back on.itself. The pin is inserted into a hole and is then bent to keep a castle nut from turning on a bolt, to hold a cotter securely in place, to hold hinge plates together, or to pin various other machine parts together. Also known as a 1/cotter key."

Cottrell precipitator A device for removing dllst or mist from a gas by passing the gas through a vertical, electrically grounded pipe. There, the particulates become ionized by corona discharge from an axial wire main­tained at a high negative voltage. The ion­ized particles migrate to the pipe's inner \vall where they collect for later removal by mechanical means.

coulomb A metric llnit forO q~antity of elec­tricity.

coulombmeter An instrument for measuring the quantity of electricity (in coulombs) by integrating a stored charge in a circllit that has a high impedance.

coulometer An electrolytic cell that is con­structed and operated In order to measure a quantity of electricity in terms of the electro­chen1ical action it produces.

coulometric titration A method of wet chem­ical analysis in which the amount of an unknown substance taking part in a chemical reaction is determined by measuring the number of coulombs that are required to reach the end point in electrolysis.

count In computer programming, the total number of times a given instruction is per­formed.

countable fault A fault that occurs in parts of electrical apparatuses and systems that com­ply vvith the constrllctional requirements of part of lEC 60079 ISA-12.02.01-1999 (IEC 60079-11 Mod). [ISA-12.02.01-1999 (ErC 60079-11 Mod)]

counter 1. A device or register in a digital processor for determil1ing and displaying the total number of occurrences of a specific event. 2. In the opposite direction. 3. A device or PC program element that can total binary events and perform on/off actions based on the value of the total. 4. A device,

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I

counteroore I cover plate�

register, or location in storage for storing counts 1. An alternate form for representing numbers or number representations such raw data that corresponds to the numerical that these numbers can be increased or representation of a signal received from or decreased by the value of another number or applied to external hardvvare. 2. The accumu­can be changed or reset to zero or to an arbi­trary value.

counterbore A drilled or bored flat-bottomed hole, often concentric with another, smaller hole.

countercurrent flow The flow of tvvo fluids in opposite directions within the san1e device, SUCl1 as a tube-in-shell heat exchanger. Contrast with counterflozu.

counterflow The flow of a single fluid in opposite directions in adjacent portions of the same device, such as a V-bend tube. Con­trast with countercurrent flo?u.

cou.oter, input The storage and buffer device betvveen an external pulse source and the computer, for example, a real-time clock or some other totalizing unit. [ISA-RP55.1-1975 (R1983)]

countershaft A secondary shaft, driven by the main shaft of a machine, and used to sup­ply power to one or more machine parts.

countersink A chamber around the edge of a circular hole that removes burrs, provides a seat for a flat-head screw or other fastener, or provides a tapered surface for a machine cen­ter to rest in.

counter/timer An instrument that counts events and measures the frequency and lor period of an AC input signal.

Counterweight 1. A mass that counterbal­ances the weight of the lifting device or load platform of an elevator or hoist so that the engine must only vvork against the payload, friction, and any remaining unbalanced machine loads. 2. Any mass that is incorpo­rated into a mechanism in order to compen­sate for an out-of-balance condition and maintain static equilibrium. Also known as "counterbalance" and "counterpoise."

counting rate The average number of ioniz­ing events that occur per unit of time, as lietermined by a counting tube or similar device.

counting-rate meter ArL instrument whose indicated output is related to the average rate of occurrence of ionizing events.

counting scale Any of several designs of weighing device in which the total vveight of a large number of identical parts is cOll1pared with the weight of one part or with the weight of a small, easily counted number of parts. The number of parts in the unkno\vn quantity is determined by automatic L.l1dica­tion, readout, or calculation.

lated total of a series of discrete inputs to a counter. 3. The discrete inputs to an accumu­latiI1g counter. See digitized signal. 4. The number of time intervals counted by the dual-slope AID converter and displayed as the reading of a panel meter, before the deGi-. :. mal point i? added.

couplant "A ·slibstan~e that is used to transmit sound waves from- an ultrasonic search unit to the surface of a test piece, thus reducing losses and improving test accuracy. Common couplants include water, oil, grease, paste, or other liquid or semisolid substances.

coupled cOI}trol-element action A type of control system action in which two or more actuating signals or control element actions are used in concert to operate one control device.

coupled reference input See cascade action. coupler 1. A physical interface between trunk

and spur or trunk and device. [ANSI/ISA­50.02, Part 2-1992] 2·. In data processing, a device that joins similar items. 3. In fiber optics, a device that joins together three or more fiber ends-splitting the signal from one fiber so it can be transmitted to two or more other fibers. "Directional," "star," and "tee" couplers are the most common variet­ies.

coupling [Eng] 1. In engineering, any device that connects the ends of adjacent parts. The connection may be rigid, thus allowing little or no relative movement, or it may be flexi­ble, thus accommodating misalig~mentand other sources of relative movement. 2. A mechanical fastening bet\veen two shafts that provides for the transmission of power and motion. Also known as "shaft coupling." [Comm] 3. In fiber optics, a device that mates two connectors. Not the same as a coupler. [Comp] 4. In computing, interdependence in a computer system.

covalence The number of covalent (electron pair) bonds that an atom can form.

covering power The ability of an electroplat­ing solution to give a satisfactory plate at low current densities, as in recesses, but not nec­essarily to build up a uniform coating. Con­trast with throzuing pou'cr.

cover plate 1. Any flat metal or glass plate that is used to cover an opening. 2. Specifi­cally, a piece of glass that is used to protect the tinted glass in a welder's helmet or gog­gles from being damaged by weld spatter.

118

covert fault Faults that can be classified as hidden, concealed, undetected, unrevealed, latent, and so on. [ANSI/ISA-84.01-1996]

cowling A metal cover, usually one that pro­vides a streamlined enclosure for an engine.

CP/M "Control Program for Microproces­sors." An early operating system for micro­computers developed at Digital Research.

cpp Characters per pica; in typographical composition of screen displays and printing, used in copyfitting calculations as the aver­age number of characters in a specific point size and typeface that will fit in one pica of horizontal space.

CPU-bound A state of program execution in which all operations are dependent on the activity of the central processor. An example is when a large number of calculations are being performed. Compare to I/O-bound.

crack 1. A fissure in a part, where it has been broken but not completely severed into two pieces. 2. The fissure or chink between adja­cent components of a mechanical assembly. 3. To incompletely sever a solid material, usually by overstressing it. 4. To open a valve, hatch, door, or other similar device by a very slight amOllnt.

cracked flow See clearance flOtu. [ANSI/ISA-ocO

75.05.01-2000] cracking In computers, breaking into com­

puters through phone lines. See hacking. _ crane A hoisting machine with a

power-driven horizontal or an inclined boom and lifting tackle.

crane hoist A mobile hoisting machine that is used principally to lift loads by means of cables. It consists of a mobile undercarriage and support structure, a power unit and winch enclosed in a cab or house (often one that s\vivels on the undercarriage), a mov­able boom, and various lifting, boom posi­tioning, and support cables.

crane scale A type of lifting device that is integral with or attached to a crane hook and that has an internal load cell that automati­cally vveighs a load as it is lifted. Where a strain-gauge load cell is used, the weight can be indicated or recorded remotely.

crank A mechanical link that can revolve about a center of rotation.

crankpin A cylindrical projection on a crank for the purpose of attaching a connecting rod.

crankshaft� 1. A straight shaft to which one or more cranks are attached. 2. A cast, forged, or machined shaft that has integral cranks, such as is used in a reciprocating automobile engine.

covert fault I creep recovery

crank throw 1. The web or arm of a crank. 2. The radial displacement of the crankpin from the crankshaft axis.

crank web The portion of a crank that con­nects a crankpin to the crankshaft or to another adjacent crankpin. Also known as crank throro.

crash A computer hardware or software mal­function that causes the system to be reset or restarted. .'

cra!e. A temp·orpry.enclosure that is used to protect an item durin'g s.hipping, handling, and storage. [ISA-RP60.11-1991]

crater 1. A spot on the face of a cutting tool where it has been worn by contact with chips. 2. A depression at the finishing end of a weld bead. .

crazing 1. A network of fine, shallow cracks at the surface of a coating, solid metal, or plastic material. 2. The development of such a network. . ·

create To open, write data to, and close a file for the first time.

creep 1. A change in output that occurs over a specific time period while the measurand and all environmental conditions are held constant. [ISA-37.1-1975 (RI982)] 2. A time-dependent plastic strain that occurs in a metal or other material under stress, usually at elevated ten1perature.

creepage distance The shortest distance along the surface of the insulating material between two conductive parts. [lEV 151- 03­37; ANSi/ISA-82.02.01-1999 (IEC61010­1Mod); ANSI/ISA-12.16.01-1998 (lEC 60079­7 Mod); ANSI/ISA-12.25.01-1998 (IEC 60079­5 Mod)]

creepage distance in air The shortest distance along the sllrface of an insulating medillffi that is in contact with air between two con­ductive parts. Note: The distance concerned here is, for example, applicable to printed cir­cuits that have no coating, where t11e insula­tion across which the creepage distance is measured is in direct contact with the air. [ISA-12.02.01-1999 (IEC 60079-11 Mod)]

creepage distance under coating The surface of an insulating medium that is covered with an insulating coating. [ANSI/ISA-12.25.01­1998 (IEC 60079-5 Mod); ISA-12.02.01-1999 (IEC 60079-11 Mod)]

creep at load The change in Olltput that occurs over time under rated load a11d with all environmental conditions and other vari­ables remaining constant. [ISA-37.8-1982 (R1995)]

creep recovery TI1e change in zero-meaSllr­and output (that occurs over) time after the

119�

I

crest I crossbar micrometer�

removal of the rated load, which had been of sound, or it n1ay mean the point at which applied for an identical time in evaluating the flow is fully chocked. the creep at load. [ISA-37.8-1982 (RI995)] critical frequency The frequency below

crest 1. The top of a screw thread. 2. The bot­ which a traveling wave of a given mode can­tom edge of a weir notch, sometimes referred to as the "sill."

crest value Peak value (of voltage, current, or any alternating signal). See peak value.

crest voltmeter An instrull1ent whose indi­cated value is the average positive peak amplitude of a sinusoidal AC electric volt­age.

crest width The distance along the crest between the sides.

crevice corrosion A type of concentration-cell corrosion that is associated with the stagnant conditions in crevices, fissures, pockets, and recesses avvay from the flow of a principal fluid stream. Here, the concentration or depletion of dissolved salts, ions, or gases such as oxygen leads to deep pitting.

crimping 1. Forming small cbrrllgations in order to set down and lock a seam, create an arc in a metal strip, or reduce the radius of an existing arc or circle. 2. Causing something to become wavy, crinkled, or warped. 3. Pinch­ing or pressing together to seal or llnite, especially the longitudinal seam of a tube or cylinder.

critical alert An alert object with an assigned priority value of 8 -15. [ISA-TR50.02, Part 9­2000]

critical angle In fiber optics, the smallest angle from the fiber axis at which a ray may be totally reflected. Determines fiber effi­ciency.

critical cooling rate The minimum cooling rate that will suppress undesired transforma­tions during a hardening heat treatment.

critical damping See damping. critical dimension 1. Generally, any pl1ysical

n1easurement whose value or accuracy is considered to be vital to the function of the relevant component or assembly. 2. In a waveguide, the cross-sectional dimension that determines the vvaveguide's critical fre­quency.

critical flow 1. The rate of flow of a fluid that is equivalent to the speed of sound in that fluid. 2. A point at which the characteristics of flow suffer a finite change. In the case of a liquid, critical flow could mean the point a. t which the flovv regime changes from laminar to transitional. It more often is used to mean "choked flow." In the case of a gas, critical flo\v may mean the point at which the veloc­ity at the vent contracta attains the veloci ty

not be maintained in a given waveguide. Critical Path Method In a Manufacturing

Execution System (MES), the use of com­puters to determine the order operations that must be executed in order to con1plete some effort in minimum' time and to determine which operations h~ve some "float" or capacity to be r~ptogrammedwithollt affect­ing that minimum time.

critical point The temperature and pressure at which two phases of a substance that are in equilibrium with each other become iden­tical, forming one phase.

critical pressure 1. The pressure of the liquid­vapor critical point. 2. The equilibrium pres­sure of a fJuid that is at its critical tempera­ture.

critical-pressure- ratio The ratio of down­stream pressure to upstream pressure that corresponds to the onset of turbulent flow in a moving stream of fluid.

critical speed 1. T11e rotational speed that corresponds to a na tural frequency of the rotor-shaft-bearing system, above which the rotor is considered flexible. 2. The speed of angular rotation at which a shaft becolues dvnamicallv unstable because of lateral reso­n~nt vibration.

critical strain The alnount of prior plastic strain tha t is just sufficient to trigger recrys­tallization when a deformed metal is heated.

critical temperature 1. The temperature of the liquid-vapor critical point, vvhich is the temperatllre above vvhich the fluid has no liquid-vapor transition. 2. The temperature of a fluid above which the fluid cannot be liq­uefied by pressure alone.

critical velocity For a given fluid, the average linear velocity that marks the upper limit of streamline flow and the lower limit of turbu­lent flo\'\! at a given temperature and pres­sure in a given confined flow path.

crop To cut off some part of an image, as in manipll1ating computer graphics.

cross-assembler An assembler progran1. that is run on a larger host computer and used to produce machine code to be executed on another, usually smaller, computer.

cross-axis acceleration See transverse accelera­tion.

crossbar micrometer An instrun1ent for determining the differences in right ascen­sion and declination of celestial objects. It consists of t'vvo bars tl1at are mounted per­

120

I

crossbar sWitch I crown glass�

pendicular to each other in th~e focal plane of speakers. Also known as a "dividing a telescope and inclined at 45

v

to the east­ netw~:k" and "loudspeaker dividing net­west pat11 of the stars. "vork.

crossbar switch A switch that has multiple cross section 1. For a given confined flow vertical and horizontal paths and an electro­n1agnetically operateli means for intercon­necting various horizontal with vertical paths.

cross-compiler A computer program that is run on a larger host computer and used for translating a high-level language program into the machine code to be executed on another computer.

cross-drum boiler A section header or box boiler in which the axis of the horizontal drum is at right angles to the center lines of the tubes in the main bank.

crossed pinning A physical configuration that allows two data terminating equipment (DTE) devices or two data COll1.munications equiplllent (DCE) devices to co~municate.

See DeE, OTE. . crosshair An inscribed line or a thin hair,

wire, or thread that is used in the optical path of a telescope, microscope, or other optical device to obtain accurate sightings or mea­SUrell1.ents. Sometimes, a pair of hairs at right angles is used, which is the original source'of the term.

1crosshead 1. A sliding block that moves back

and forth between guides and that contains a•.•.:.·.··· .. wrist pin for converting reciprocating motion ,:r ..

>~I into rotary motion. 2. A device that is designed to extrude material at an angle. Used most extensively at the discharge end of an extruder in a wire-coating operation.

cross-modulation Carrier and signal har­monics of one or more channels that appear in other channels of a system. In the case of a large number of cross-modulation products, the resultant cross-talk noise approaches the characteristics of fluctuation noise (AM).

crossover A conductor that rlins through cable and connects to differently numbered pins at each end.

crossover frequency 1. The frequency at which a dividing netyvork delivers equal power to upper-band and lower-band chan­nels. 2. The frequency at which the asymp­totes to the constant-amplitude and constant-velocity portions of the fre­quency-response curve of an acoustic record­ing system intersect. Also kI10\tvn as transition frequency and turnover frequency.

crossover network A selective network that divides the audio-frequency output of an amplifier into two or more bands of frequen­cies in order to supply two or n10re loud-

path or a given elongated structural member,� the dimensions, shape, or area that are deter­�mined by its intersection \vith a plane per­�pendicular to its longitudinal axis. 2. In� cb.aracterizing interactions between moving� atomic particles, the probability per unit flux� and per unit tiI)1e that a given in teraction� \\Till ocCur. .. ..

cross sensitivity; cross-axis sensitivity See transverse sensitivitl/.

cross talk 1. The u~wanted energy that is transferred from one circuit, called the"dis­turbing" circuit, to another circuit, called the "disturbed" circuit. [ISA-RP55.1-1975 (R1983)] 2. The unwanted signals in a chan­nel that originate from one or more channels in the same communication system. 3. Sig­nals electrically coupled from another circuit, tlsually llndesirably, but sometimes for use­ful purposes.

crosstalk Interference caused by cross coupling between adjacent circuits or by the intermod­ulation of two or more carrier channels. It produces unwanted signal(s) in one circuit when the signal is present in the other.

cross-wire weld A resista11ce weld that is made by passing a controlled electric current through the junction of a pair of crossed wires or bars. Used extensively to make mesh or screening. "'

crowbar An action in a pOvver supply that effectively creates high overloali on the actu­ating member of a protective device. Crow­bar action may be initiated by a slight increase in current or voltage.

crowbar voltage protector A separate circuit that monitors the output of a po\\rer supply and instantaneously throws a short circuit (or crowbar) across output terminals of the power supply whenever a preset voltage limit is exceeded. Silicon controlled rectifier (SCR) is often used as the cro\vbar device. See SeRe

crown 1. The part of a drill bit that is inset with diamonds. 2. The vertex of a structural arch or arched surface. 3. The domed top of a furnace or kiln. 4. The central portion of sheet rna terial tha t is sUghtlYthicker than at the edges. 5. Any raised central portion of a nominally flat surface.

crown gl :lSS An optical glass of alkali-lime­silica composition with an index refraction that is usually 1.5 to 1.6.

121 t

I

crown sheet I cumulative SUlll cnart

J (J..'

crown sheet In a firebox boiler, the plate that forms the top of the furnace.

CRT display 1. Catrlode ray tube (video screen). 2. The alphanumeric and/or graphic image shown on a cathode ray tube.

crucible A pot or vessel that is made of a high-melting-point material, such as a ceramic or refractory metal. Used for melting metals and other materials.

crude oil Unrefined petroleum. crush 1. A casting defect that is caused by the

displacement of sand as the mold is closed. 2. The buckling or breaking of a section of a casting mold because of incorrect register as the mold is closed.

cryogenic Any process that is carried out at very low temperature, usually considered to be -60°F (-SO°C) or lower.

cryogenic fluid A liquid that boils below ­123°Kelvin (-23S0p, -IS0°C) at one atmosphere absolute pressure. ,

cryometer A thermometer for measuring very low temperatures.

cryoscope A device for determining the freezing point of a liquid.

cryostat An apparatus for establishing the very low-temperature environment that is needed for carrying out a cryogenic opera­tion.

crystalline fracture A type of fractllre surface appearance that is characterized by numer­ous brightly reflecting facets caused by cleavage fracture of a polycrystalline mate­rial.

crystalloluminescence Light produced by the crystallization of chemicals.

crystal oscillator A device for generating an AC signal whose frequency is determined by the properties of a piezoelectric crystal.

crystal spectrometer An instrument that uses the diffraction from a crystal to determine the component wavelengths in a beam of X-rays or gamma rays.

CSIA Control Systems Integrators Associa­tion; group formed by NEMA to address programs for control system engineer regis­tration, ISO 9000 qlIality program, strategic alliances/joint ventures, business manage­ment, and business practices. Affiliated with System Integrators Grolip vvithin Automa­tion Products and Systems section of Indus­trial Automation Division.

CSMA/CD Carrier Sense Multiple Access/ with Collision Detection; media access method (ISO data link layer 2) for local area networks (LANs); IEEE 802.3-like standard by Intel, Xerox, and DEC in \vhich contention betvveen hvo or more stations is resolved by

detecting the simultaneous transmission and causing each to retry after waiting a prede­termined time; the time is different for each station on network and usuallv several microseconds. .I

CSU Channel service unit; (cumulative sum) algorithm. See cornpressor.

CSV Comma-separated variable; format method of saving data to electronic memory expressly for sharing data between comput­ers or applicatiC?ns. Often used to transfer column5' of text and numerital data.

CTD Cum.ulative·'trauma disorder(s); physiologicai prqblep1.s that can OCCllr in users of equipment with ergonomically poor design; often used in reference to, but not limited to, the broad category of problems related to repetitive wrist movements linked to extensive data entry in computers. The problem occurs among many other occupa­tions, but the highest rates are among meat packers (OSHA); accounts for 61 percent of all private-sector occupational illnesses in 1991 according to the Bureau of Labor Statis­tics; also called repetitive strain injury (RSI).

CTS Clear to send; modem interface control signal (typically, EIA RS-232/422) indicating readiness to accept data from DeE. Also, car­pal tunnel syndrome; the irritation of tendon sheath and lining involving the median nerve at the human wrist; can affect typists, computer operators, and anyone who uses hand tools. Also, cubital tllnnel syndrolne, irritation of tendon sheath and lining involv­ing median nerve at the human elbow; cal1 affect phone operators, drivers, and those who keep arms in flexed positions or con­stantly lean on their elbows.

cubicle 1. An enclosed control center with front, rear, top, and sides but with or without a bottom. 2. Any small room or enclosure. 3. An enclosure, usually free standing, that houses high-voltage electrical eqllipment.

CUI Character-based user interface; pro­vides access to any applications that reside on the server or mainframe, regardless of any incompatibilities that exist between worksta­tions or applications.

cumulative dose The total amount of pene­trating radiation that is absorbed by the whole body, or by a specific region of the body, during repeated exposllres.

cumulative sum chart (CUSUM chart) A sta­tistical control chart on which the cUffittlative SLIm of deviations is plotted over a period of time. It often has a sliding V-shaped mask for comparing the plot with allowable limits.

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I

cup fracture I cutoff

cup fracture A mixed-mode fracture in duc­ current proportioning The output form of tile metals, usually observed in round tensile controller that provides current proportional specimens, in which part of the fracture to the amount of control required. Normally, occurs under plane-strain conditions and the 4 to 20 rnA current proportioning band. remainder under plane-stress conditions. As a result, in a round tensile bar one of the mat­ing fracture surfaces looks like a n1.iniature cup and the other like a truncated cone. Also known as "cup-and-cone fracture."

cupping 1. The first step in deep drawing. 2. The fracture of severely worked rod or wire, where one of the fracture surfa.c~s is roughly conical and the other cup-shaped.

Curie (Ci) The standard unit of measure for the radioactivity of a substance. It is defined as the quantity of a radioactive nuclide that is disintegrating at the rate of 3.7 x 1010 disin­tegrations per second.

curing 1. The process of allowing a substance such as a polymeric adhesive or poured con­crete to rest under controlled conditions, which may include clamping, heating, or providing residual moisture, until it under­goes a slow chemical reaction to reach final bond strength or hardness. 2. In thermoplas­tics molding, stopping all movement for an interval before releasing the pressure of a

~ mold so that the molded part has sufficient time to stabilize.

current The rate of flow of an electrical charge in an electric circuit, measured in amperes (A or amps). One Ampere = 1 cou­lomb per second. Analogous to the rate of flow of water in a pipe.

current anlplification For a given amplifier, the ratio of current delivered to the output circuit to the corresponding current supplied to the input circuit.

current clamp A device for measuring cur­rent or indicating current vvaveforms with­out interrupting the current path of the circuit in which it is measured or under test. [ANSI/ISA-82.02.04-1996 (IEC 61010-2-032)

current limit A circuit or device that is designed to limit current flo\v to a certain value. It may also be used to set limits, high and low, which allows the current to be at a level between the limits.

current loop (20 rnA) A serial transmission standard that is widely used for video dis­play units (VDUs) and teletypes. Zero and 1 are represented by the absence or presence of a current (20 rnA).

current meter Anv of a \-vide variety of devices for meas~rirlg AC or DC electric cur­rent, including moving-coil, moving-iron, electronic, and electrodynamic instruments. See velocity-type j1oIvnleter.

current-to-pressure transducer (lIP) A device� that receives an analog electrical signal and� converts it into a corresponding air pressure.� Example: 4-20 rnA input 3-15 psi output.�

Cl1rrent transformer An instrument trans­�former that is designed to have its primary� winding copt:l~cted in ~~Eles with a cirCllit� that carries the current being measured or� controlled.�

current word address (CWA) The memory� address of a word that is currently being� operated on.�

cursor 1. A symbol that is used in the opera­tion of keyboard-video displays to indicate on the display screen the physical location of the next character to be entered. [ISA-RP55.1-1975 (R1983)] 2. The tracking and selecting "loca­

. tor symbol" on a video screen. It is manipu­lated with keyboard, mouse, trackball, touch screen, and so on, and used to retrieve or enter data, command functions, and actions.

curvature of field A defect in an optical lens or system that causes the focused image of a plane field to lie along a curved surface rather than a flat plane.

curve fit The process of determining the coef­ficients in a curve by mathematically fitting a given set of data to that curve class. An example is linear curvefit, or nth order poly­nomial curvefit.

curve tracer An instrument that characterizes a wide range of devices by displaying para­metric responses as a two-dimensional plot of Cllrrent versus voltage.

custody transfer The act of transferring own­ership of a flllid for money or the equivalent.

custom LSI A large-scale integrated (LSI) cir­cuit that is designed for a specific purpose and which therefore has a dedicated func­tion.

CUSUM Cumll1ative sum; llsed in statistical process control (SPC).

CUSUM chart (cumulative sum chart) A sta­tistical control chart on which the cumulative sum of deviations is plotted over a period of time and that often has a sliding V-shaped mask for comparing the plot with alloyvable limits.

cut-and-paste A feature of Windows that lets yOll select information from one file and move or copy it to another file (or another location in the same file).

cutoff 1. The parting line on a compres­sion-molded plastics part. Also known as

123�

cutoff tool 1 cycle�

SH Y-AIM ACTION

3.36

LIMIT

-2• -336 ACTION

-SL I I I j J j I I I I I I I I I I I I j I I I I I I I I I I I I o 11 22 33 44 55 66 LIMIT

SAMPLE TIME

CUSUM Chart

"flash groove" and "pinch-ofr" 2. The point in the stroke of an engine at which admission of the working fluid to the cylinder is shut off. 3. The time reqllired to shut off the flow of working fluid into a cylinder.

cutoff tool A lathe tool that has a narrow cut­ting edge that is used to sever a finished piece from the remaining bar stock. Also known as a parting tool.

cutoff valve A qllick-acting valve that is used to stop the flow of working fluid into an engine cylinder.

cutoff wavelength 1. In fiber optics, the wave­length at which modes other than the funda­mental mode are not propagated. 2. For single-mode fiber-optic cable, the wave­length above which the fiber exhibits single­mode operation.

cutoff wheel A thin abrasive wl1eel that is used to cut stock or to make slots in a part.

cutout alarm An alarm that is designed to not function during certain states of other oper­ating condition(s) or parameter(s), often dl1r­ing start-up, shutdown, or critical stages of process, and so on.

cuts-only In video development, an editing system that is limited to direct edits from one clip to the next with no transitions between scenes.

cutter A cutting tool, especially a rotary, toothed cutting wheel.

cutter bar A supporting member for the cut­ting tool in a lathe or other mac11ine tool.

cutting angle The angle between the face of a cutting tool and the uncut stock surface.

cutting edge 1. In a diamond or ceramic tool, the point or edge of the insert material that actually cuts the work. 2. Generally, the sharpened edge of any cutting tool that con­tacts the work during machining.

cutting fluid In a metal-cutting operation, any liquid that is introduced into the area where the tool contacts the work, especially a

liquid that is used to provide lubrication at the cutting edge, to carry away the heat gen­erated during machining, and to flush out chips or other machining debris. Some cut­ting fluids have chemical compounds that react with the tool and material bei11g cut in order to enhance cutting action.

cutting speed The relative velocity between the cutting tool and workpiece along the main directio.n of clltting. Also known as peripheral spe?p:.

cutting tool . A sh~rp-edged, single-point or toothed tool that comes in contact with the workpiece and removes stock il;_ a machining operation. Also known as a cutter.

cutting torch A device for producing a con­trolled flame that has an additional supply line for introducing a jet of oxygen into the flame. It cuts metal and other materials by first heating a small area, then rapidly oxi­dizing and mefting the material along a thin line "vhen the jet of oxygen is turned on. Usu­ally a special plasma torch is needed for stainless steel because of its oxidation resis­tance.

C rating See valve flow coefficient.v Cv Flow efficiency factor. The flow rate (U.S.

gallons per minute) across a restriction (e.g., valves, fittings, etc.) at 1 psig pressure drop.

cyan A color hue that transniits only blue and gre~n light, with no red, from the screen view. Cyan reflects only green and blue light and absorbs red light on paper using fOl1r­color process inks.

cyaniding A surface-hardening process simi­lar to carbonitriding that produces a carbon­and nitrogen-rich surface layer on steel by immersing parts in a bath of molten cyanide salts. Cyaniding can also be done in the gas phase.

cybernetics The branch of learning that brings together theories and stlIdies on com­munication and control in living organisms and machines.

cycle 1. An interval of space or time in which one set of events or phenomena is com­pleted. 2. Any set of operations that is repeated regularly in the same sequence. The operations may be subject to variations in each repetition. 3. In any repetitive variable process, the variation of a given variable through one complete range of values. 4. To run a machil1e through a complete set of operating steps. 5. The fllndamental time interval for operations inside tIle computer. 6. A condition in a sequential circuit. From an initial, unstable state the circuit passes

124�

I

cycle index / cylinder liner

through more unstable states before reaching cyclic shift A shift in which the data moved a stable state. out of one end of the storing register are

cycle index The number of times a cycle has re-entered into the other end, as in a closed been executed or the difference, or the nega­ loop. tive of the difference, between the number that has been executed and the number of repetitions desired.

cycle life The specified minimum number of cycles over which a device will operate as specified vvithout changing its performance beyond the specified tolerance. [ANSI/ISA­75.05.01-2000; ANSI/ISA-51.1-1979 (R1993)]

cycle progress A feature of a timer or counter that s110ws the progression point in time or count cycle. Cycle progress can be shown by a digital display or a pointer progressing through the scale on a dial.

cycle stealing 1. A control feature that delays the execution of a program in order to allow an I/O device to communicate with main storage without changing the logical condi­tion of the cpu. [ISA-RP55.1-1975 (R1983)] 2. Data that is transferred over the data bus during a direct memory access while little disruption occurs to the normal operation of

" the microprocessor.� ~ycle time 1. The time a computer needs to ~

f, read from or write into the system memory. If� 1 system memory is core, the read cycle time ': includes a write-after-read (restore) subcycle.

Cycle time is often used as a measure of com­puter performance, since cycle time is a mea­sure of the tinle required to fetch an instruc­tion. 2. The time, usually expressed in sec­onds, for a controller to complete one on/off cycle.

cyclic A condition of either steady-state or transien t oscillation of a signaI around the nominal value.

cyclic code A forn1. of Gray code that is used for expressing numbers. When coded values are arranged in the numeric order of real val­ues, each digit of the coded value assumes its entire range of values alternately in ascend­ing and descending order.

cyclic redundancy check (CRC) An error­detection scheme, usually implemented by hardware, in \vhich a check character is gen­erated by taking the remainder, after divid­ing all the serialized bits in a block of data by a predetermined binary number. This remainder is then appended to the transmit­ted data, recalculated, and compared at the receiving point to verify data accuracy.

cyclic redundancy check character (CRe) A character that is used in a modified cyclic code to detect and correct errors.

Cycling Periodic, repeated variation in a con­trolled variable or process action.

cycling life The number of cycles over which a device will operate without changing its performance beyond tolerance. [f\.NSI/ISA­51.1-1979 (R1993); ANSI/ISA-75.05.01-2000]

cyclograph A device. for electromagnetically sorting or testipg...metafparts by mea11S of the pattern that is produced on a cathode ray tube when a sample part is placed in an elec­tromagnetic sensing coil. The CRT pattern is different in shape for different values of car­bon content, case depth, core hardness, or other metallurgical properties.

cyclotron A device that utilizes an alternating electric field between electrodes that are positioned in a constant magnetic field in order to accelerate ions or charged subatomic particles to high energies.

cylinder 1. A domed, closed storage tank for hot water. Also known as a stora(cse calorifier. 2. A strong, thick-walled container for stor­�ing and transporting compressed gases. 3. A� round, straight-walled cavity, closed at one� or both ends, that a piston rides in to convert� the potential energy in pressurized gas or liq­�uid into linear mechanical motion and pOlATer� or to utilize mechanical povver so as to com­�press a fluid.�

cylinder, disk All like-numbered tracks on a disk pack. A portion of the disk tl1at can be recorded or reproduced wit110ut moving the heads.

cylinder block A massive piece of metal, usually made by casting, that contains the piston chambers of a multicylinder engine or compressor. Also known as the block or engine block.

cylinder bore The inside diameter of a piston chamber.

cylinder head The cap, which usually has a specially shaped recess, that is used to close the end of a piston chamber in a reciprocat­ing engine pump, or compressor. Usually, it provides valve openings, spark plug taps, and other penetrations necessary for machine operation.

cylinder liner A separate cylindrical sleeve that is inserted into a piston chamber in order to provide a cylinder "vall that has properties different from those of the cylin­der block. Normallv used to furnish a better­wearing material f~r piston rings than the

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cylindrical cam / cylindrical lens

block, that is, a cast-iron liner in an alumi­�num block.�

cylindrical cam A mechanism that consists of a cylinder that rotates on its longitudinal axis and causes linear motion parallel to that axis in a cam follower, which rolls in a groove cut in the cylindrical surface.

cylindrical lens A lens that is cylindrical in cross section, so it is curved in one direction but not in the perpendicular direction. Used to expand a laser beam into a plane of light.

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