programmable logic controllers plc’s التحكم المنطقى المبرمج

PProgrammable rogrammable LLogic ogic CControllersontrollers

PLC’sPLC’s

المنطقى التحكمالمبرمج

OverviewOverview

Course Contents Course Contents

What is a PLC ?What is a PLC ?

HistoryHistory

Overview of TechnologyOverview of Technology

PLC Configuration and SelectionPLC Configuration and Selection

Programming PLC’sProgramming PLC’s

Introductions to PLCIntroductions to PLC

PLC HardwarePLC Hardware

Input / Output Input / Output

ProcessingProcessing

Input DevicesInput Devices

Output DevicesOutput Devices

Course ContentsCourse Contents

Programming

Internal

Relays

Timers

Counters

Projects

What is a PLC ?What is a PLC ?

What is a PLC ?What is a PLC ?A PLC works by looking at its inputs and depending on A PLC works by looking at its inputs and depending on

their state, and the user entered program, turns on/off their state, and the user entered program, turns on/off

outputs.outputs.

A PLC can be thought of as: A PLC can be thought of as:

Industrial ComputersIndustrial Computers with specially designed architecture with specially designed architecture

in both their central units (the PLC itself) and their in both their central units (the PLC itself) and their

interfacing circuitry to field devices (input / output interfacing circuitry to field devices (input / output

connections to the real world).connections to the real world).

CommercialCommercial AndAnd Industrial Industrial ComputersComputers

Commercial Computer

Industrial Computer

History 1/5History 1/5

Early control systems consisted of Early control systems consisted of

huge control boards consisting of huge control boards consisting of

hundreds to thousands of hundreds to thousands of

electromechanical relays.electromechanical relays.

An Engineer would design the An Engineer would design the

system logic.system logic.

Electricians would receive a Electricians would receive a

schematic outline of logic then schematic outline of logic then

implement the logic with relays.implement the logic with relays.

|/|

CR3

CR3 M1

PB1 LS1 SOL2

PB2LS1

LS3

LS4


The schematic was commonly called “Ladder Schematic”The schematic was commonly called “Ladder Schematic”

The Ladder displayed all switches, sensors, motors, The Ladder displayed all switches, sensors, motors,

valves, relays etc in the system.valves, relays etc in the system.

Problems: Long implementation time, Mechanical Problems: Long implementation time, Mechanical

dependence, Any system logic design change required dependence, Any system logic design change required

the power to the control board to be isolated stopping the power to the control board to be isolated stopping

productionproduction


General Motors was among the first to recognize a need to General Motors was among the first to recognize a need to

replace the systems “wired control board”replace the systems “wired control board”

Hydromantic Division of GM specified the design criteria for Hydromantic Division of GM specified the design criteria for

the programmable controller in 1968.the programmable controller in 1968.

Goal – Goal – Eliminate the high cost associated with inflexible, Eliminate the high cost associated with inflexible,

Relay controlled systems.Relay controlled systems.

History 4/5History 4/5New Controller Specifications:New Controller Specifications:

– Solid State SystemSolid State System

– Computer FlexibilityComputer Flexibility

– Operate in Industrial Environment (vibrations, heat, Operate in Industrial Environment (vibrations, heat,

dust etc.) dust etc.)

– Capability of being reprogrammedCapability of being reprogrammed

– Easily programmed and maintained by electricians Easily programmed and maintained by electricians

and technicians.and technicians.


In 1969 Gould Modicon developed the first PLC. In 1969 Gould Modicon developed the first PLC.

Strength – Programmed with Ladder LogicStrength – Programmed with Ladder Logic

Initially called Programmable Controllers PC’s Initially called Programmable Controllers PC’s

– Now PLC’s, Programmable Logic ControllersNow PLC’s, Programmable Logic Controllers

PLC’s have evolved from simple on/off control to being PLC’s have evolved from simple on/off control to being

able to communicate with other control systems, provide able to communicate with other control systems, provide

production reports, schedule production, diagnose production reports, schedule production, diagnose

machine and process faults.machine and process faults.

Relay Logic vs. PLC & Ladder Relay Logic vs. PLC & Ladder LogicLogic

|/|

CR3

CR3 M1

PB1 LS1 SOL2

PB2LS1

LS3

LS4

ProgrammableLogic

Controller

Inputs Outputs

CR

X4

X0 X1 Y0

Y1

| | | | ( )

X3X2 M0

| | | | ( )

| |

|/|M0

( )| |X5

PLC ConfigurationPLC Configuration

RACK

SHOE BOX (UNITARY) MICRO

The Configuration of PLCThe Configuration of PLCThe configuration of PLC refers to the packaging of the The configuration of PLC refers to the packaging of the

components.components.

Typical configurations are listed below from largest to smallest.Typical configurations are listed below from largest to smallest.

– Rack TypeRack Type : : A rack is often large (up to 18” by 30” by 10”) and

these use a range of modules that use together to build up a

system.

– ShoeboxShoebox: A compact, all-in-one unit that has limited expansion : A compact, all-in-one unit that has limited expansion

capabilities. Lower cost and compactness make these ideal for capabilities. Lower cost and compactness make these ideal for

small applications.small applications.

– MicroMicro: These units can be as small as a deck of cards. They : These units can be as small as a deck of cards. They

tend to have fixed quantities of I/O and limited abilities, but costs tend to have fixed quantities of I/O and limited abilities, but costs

will be lowest. will be lowest.

Most Basic of PLC SystemsMost Basic of PLC SystemsIn the most basic of PLC systems, a self contained (shoe box) In the most basic of PLC systems, a self contained (shoe box)

PLC has 2 terminal blocks, one for Inputs and one for OutputsPLC has 2 terminal blocks, one for Inputs and one for Outputs

Today, most PLC’s in this category are know as Today, most PLC’s in this category are know as MicrologixMicrologix. .

Typically they provide front panel LED status indication of I/O and Typically they provide front panel LED status indication of I/O and

Processor statesProcessor states

Programmable Controller

Inputs Outputs

CR

Modular Chassis Based PLC’sModular Chassis Based PLC’s

The vast majority of PLC’s installed today are modular chassis The vast majority of PLC’s installed today are modular chassis

based systems consisting of:based systems consisting of:

1.1. Processor Module (CPU)Processor Module (CPU)

2.2. Input & Output ModulesInput & Output Modules

3.3. ChassisChassis

4.4. Power SupplyPower Supply

Modular Chassis Based PLC’sModular Chassis Based PLC’s

Sizing of PLCSizing of PLC

Micro PLCs: I/O up to 32 pointsMicro PLCs: I/O up to 32 points

Small PLC: I/O up to 128 pointsSmall PLC: I/O up to 128 points

Medium PLC: I/O up to 1024 pointsMedium PLC: I/O up to 1024 points

Large PLC: I/O up to 4096 pointsLarge PLC: I/O up to 4096 points

Very Large: I/O up to 8192 pointsVery Large: I/O up to 8192 points

Overview of TechnologyOverview of Technology

Basic PLC SchemaBasic PLC Schema

CPUCPU

Power SupplyPower Supply

MemoryMemory

Input Module Input Module

Output Module Output Module

Programming devicesProgramming devices

CommunicationsCommunications

Expansion ConnectionsExpansion Connections

CPU ModuleCPU Module

CPU Module CPU Module Cont’dCont’d

The Central Processing Unit (CPU) Module is the brain of the The Central Processing Unit (CPU) Module is the brain of the

PLC.PLC.

CPU architecture may differ from one manufacturer to another, CPU architecture may differ from one manufacturer to another,

but in general, most CPUs follow this typical three-component but in general, most CPUs follow this typical three-component

organization (Processor, Memory, Power Supply) organization (Processor, Memory, Power Supply)

The term CPU is often used interchangeably with the word The term CPU is often used interchangeably with the word

ProcessorProcessor; however, the CPU encompasses all of the necessary ; however, the CPU encompasses all of the necessary

elements that form the intelligence of the system—the processor elements that form the intelligence of the system—the processor

plus the memory system and power supplyplus the memory system and power supply

PLC Operating CyclePLC Operating Cycle

SelfCheck

ExecuteCode

ScanInputs

UpdateOutputs

PLC ProgramSCAN

The basic function of a The basic function of a

programmable controller is to programmable controller is to

read all of the field input devices read all of the field input devices

and then execute the control and then execute the control

program, which according to the program, which according to the

logic programmed, will turn the logic programmed, will turn the

field output devices ON or OFF.field output devices ON or OFF.

A PLC works by continually A PLC works by continually

scanning a programscanning a program

Input Scan

Program ScanOutput Scan

Housekeeping

START

Each ladder rung is scanned using the data in the Input file. The resulting status (Logic being solved) is written to the Output file (“Output Image”).

The status of external inputs (terminal block voltage) is written to the Input image (“Input file”).

The Output Image data is transferred to the external output circuits, turning the output devices ON or OFF.

Internal checks on memory, speed and operation. Service any communication requests, etc.

PLC Operating Cycle Cont’d.PLC Operating Cycle Cont’d.

Scan TimeScan Time

The scan time is the total time the PLC takes to complete The scan time is the total time the PLC takes to complete

the program and I/O update scansthe program and I/O update scans

Scan Time Cont’d Scan Time Cont’d

The program scan time generally depends on two The program scan time generally depends on two

factors:factors:

– the amount of memory taken by the control programthe amount of memory taken by the control program

– the type of instructions used in the program (which the type of instructions used in the program (which

affects the time needed to execute the instructions)affects the time needed to execute the instructions)

The time required to make a single scan can vary from a The time required to make a single scan can vary from a

few tenths of a millisecond to 50 milliseconds.few tenths of a millisecond to 50 milliseconds.

Power SupplyPower SupplyThe system power supply plays a major role in the total system

operation.

Its responsibility is not only to provide internal DC voltages to the

system components (i.e., processor, memory, and input/output

interfaces), but also to monitor and regulate the supplied voltages and

warn the CPU if something is wrong.

PLC power supplies require input from an AC power source; however,

some PLCs will accept a DC power source. Most PLCs, however,

require a 120 VAC or 220 VAC power source, while a few controllers

will accept 24 VDC.

MemoryMemory

The memory includes pre-programmed ROM memory The memory includes pre-programmed ROM memory

containing the PLC’s operating system, driver programs containing the PLC’s operating system, driver programs

and application programs and the RAM memory.and application programs and the RAM memory.

PLC manufacturer offer various types of retentive PLC manufacturer offer various types of retentive

memory to save user-programs and data while power is memory to save user-programs and data while power is

removed, so that the PLC can resume execution of the removed, so that the PLC can resume execution of the

user-written control program as soon as power is user-written control program as soon as power is

restored.restored.

Memory cont’dMemory cont’d

Many PLCs also offer removable memory modules, Many PLCs also offer removable memory modules,

which are plugged into the CPU module.which are plugged into the CPU module.

Memory can be classified into two basic categories: Memory can be classified into two basic categories:

volatile and non-volatile.volatile and non-volatile.

- - Volatile memoryVolatile memory is that which loses state (the is that which loses state (the

stored information) when power is removed.stored information) when power is removed.

- - Non-volatile memoryNon-volatile memory, on the other hand, , on the other hand,

maintains maintains the information in memory even if the the information in memory even if the

power is power is interrupted. interrupted.


Some types of memory used in a PLC Some types of memory used in a PLC include:include:

ROM (Read-Only Memory)ROM (Read-Only Memory)

– This memory is permanent and cannot be erased. It is

often used for storing the operating system for the PLC.

Memory cont’dMemory cont’dRAM (Random Access Memory)RAM (Random Access Memory)

– This memory is fast, but it will lose its contents when power

is lost, this is known as volatile memory. Every PLC uses

this memory for the central CPU when running the PLC.

– For the most part, today’s programmable controllers use

RAM with battery support for application memory.

– Random-access memory provides an excellent means for

easily creating and altering a program, as well as allowing

data entry


EEPROM (Electrically Erasable Programmable Read-Only Memory)EEPROM (Electrically Erasable Programmable Read-Only Memory)

– This memory can store programs like ROM. It can be

programmed and erased using a voltage, so it is becoming more

popular than EPROMs.

– Several of today’s small and medium-sized controllers use

EEPROM as the only memory within the system. It provides

permanent storage for the program and can be easily changed

with the use of a programming device (e.g., a PC) or a manual

programming unit.

Application MemoryApplication Memory

The application memory stores

programmed instructions and any

data the processor will use to

perform its control functions.

The controller stores all data in

the data table section of the

application memory, while it

stores programmed instructions in

the user program section.

Application Memory Cont’dApplication Memory Cont’d

The input table is an array

of bits that stores the status

of digital inputs connected to

the PLC’s input interface.

The maximum number of

input table bits is equal to the

maximum number of field

inputs that can be connected

to the PLC

Application Memory Cont’dApplication Memory Cont’dThe output table is an array of

bits that controls the status of

digital output devices that are

connected to the PLC’s output

interface. The maximum number

of bits available in the output

table equals the maximum

number of output field devices

that can interface with the PLC.

I/O ModulesI/O Modules

Input and output (I/O) modules connect the PLC to Input and output (I/O) modules connect the PLC to

sensors and actuators.sensors and actuators.

Provide isolation for the low-voltage, low-current signals Provide isolation for the low-voltage, low-current signals

that the PLC uses internally from the higher-power that the PLC uses internally from the higher-power

electrical circuits required by most sensors and actuators.electrical circuits required by most sensors and actuators.

Wide range of I/O modules available including: digital Wide range of I/O modules available including: digital

(logical) I/O modules and analog (continuous) I/O (logical) I/O modules and analog (continuous) I/O

modules.modules.

Inputs ModulesInputs Modules

Inputs come from sensors that translate physical or Inputs come from sensors that translate physical or

chemical phenomena into electrical signals.chemical phenomena into electrical signals.

The simplest form of inputs are digital/discrete in AC/DC.The simplest form of inputs are digital/discrete in AC/DC.

In smaller PLCs the inputs are normally built in and are In smaller PLCs the inputs are normally built in and are

specified when purchasing the PLC.specified when purchasing the PLC.

For larger PLCs the inputs are purchased as modules, or For larger PLCs the inputs are purchased as modules, or

cards, with 8,16, 32, 64, 96 inputs of the same type on cards, with 8,16, 32, 64, 96 inputs of the same type on

each card.each card.

Inputs Modules Inputs Modules Cont’dCont’d The list below shows typical ranges for input The list below shows typical ranges for input

voltages.voltages.

5 Volts DC TTL level 5 Volts DC TTL level

24 Volts AC/DC24 Volts AC/DC



220 Volts 220 Volts AC/DCAC/DC

An AC/DC Input Block diagram

Circuit

SOURCING vs. SINKINGSOURCING vs. SINKING

Sensor With PNP Output

(Sourcing)

Sensor With NPN Output

(Sinking)

Sinking DC InputsSinking DC Inputs

When a PLC input card does not have a common but it has a V+

instead, it can be used for NPN sensors. In this case the current

will flow out of the card (sourcing) and we must switch it to ground.

Sourcing DC InputsSourcing DC Inputs

When we have a PLC input card that has a common then we can

use PNP sensors. In this case the current will flow into the card

and then out the common to the power supply.

RulesRules

Sourcing field devices must be connected to

sinking I/O cards

Sinking field devices must be connected to

sourcing I/O cards

Device connectionsfor an AC input module for DC input module

18/04/2318/04/23

Input DevicesInput Devices

PushbuttonsPushbuttons

Selector SwitchesSelector Switches

Limit SwitchesLimit Switches

Level SwitchesLevel Switches

Photoelectric SensorsPhotoelectric Sensors

Proximity SensorsProximity Sensors

Motor Starter ContactsMotor Starter Contacts

Relay ContactsRelay Contacts

Thumbwheel SwitchesThumbwheel Switches

Outputs ModulesOutputs ModulesOutput modules rarely supply any power, but instead act as Output modules rarely supply any power, but instead act as

switches.switches.

External power supplies are connected to the output card and External power supplies are connected to the output card and

the card will switch the power on or off for each output.the card will switch the power on or off for each output.

A common choice when purchasing output cards is A common choice when purchasing output cards is relays, relays,

transistors or triacstransistors or triacs..

Relay are the most flexible output devices. They are capable Relay are the most flexible output devices. They are capable

of switching both AC and DC outputs. But, they are slower, of switching both AC and DC outputs. But, they are slower,

cost more, and they will wear out after millions of cycles. cost more, and they will wear out after millions of cycles.

An AC Output

Circuit

DC OutputDC Output

As in DC inputs, DC output modules may have either sinking or

sourcing configurations. If a module has a sinking

configuration, current flows from the load into the module’s

terminal, switching the negative (return or common) voltage to

the load. The positive current flows from the load to the

common via the module’s power transistor.

In a sourcing module configuration, current flows from the

module into the load, switching the positive voltage to the load

An Example of a 24Vdc Output Card With a Voltage Input (Sourcing)

An Example of a 24Vdc Output Card (Sinking)

RelaysRelays

When using relay outputs it is possible to have each output isolated from the

next. A relay output card could have AC and DC outputs beside each other.

Relay outputs are usually used to control up to 2 amps or when a very low

resistance is required. Transistor outputs are open collector common emitter

or emitter follower

An Example of a Relay Output Card

OutputsOutputs Typical output voltages are listed below, Typical output voltages are listed below,

5 Volts DC TTL level5 Volts DC TTL level

24 Volts AC/DC 24 Volts AC/DC



220 Volts 220 Volts AC/DCAC/DC

WARNING: Always check rated voltages and currents for PLCs and WARNING: Always check rated voltages and currents for PLCs and

never exceed.never exceed.

18/04/2318/04/23

Output DevicesOutput Devices

ValvesValves

Motor StartersMotor Starters

SolenoidsSolenoids

Control RelaysControl Relays

AlarmsAlarms

LightsLights

FansFans

HornsHorns

Programmable controller I/O connection diagram

Analogue CardsAnalogue Cards

Typical Analogue Input Typical Analogue Input

signals are:signals are:

– Flow sensorsFlow sensors

– Humidity sensorsHumidity sensors

– Pressure sensorsPressure sensors

– Temperature sensorsTemperature sensors

– VibrationVibration

Analogue Output signals Analogue Output signals

control:control:

– Analogue ValvesAnalogue Valves

– Variable Speed DrivesVariable Speed Drives

Typical Analogue Signal Typical Analogue Signal

LevelsLevels

– 4 - 20mA4 - 20mA

– 1 - 5 Vdc1 - 5 Vdc

– 0 - 10 Vdc0 - 10 Vdc

– -10 – 10Vdc-10 – 10Vdc

Analogue Inputs/OutputsAnalogue Inputs/Outputs

Analogue input cards convert continuous signals via a Analogue input cards convert continuous signals via a

A/D converter into discrete values for the PLCA/D converter into discrete values for the PLC

Analogue output cards convert digital values in then PLC Analogue output cards convert digital values in then PLC

to continuous signals via a D/A converter.to continuous signals via a D/A converter.

Resolution can be important in choosing an applicable Resolution can be important in choosing an applicable

cardcard

Programming DevicesProgramming DevicesPLC manufacturers have always maintained an easy human

interface for program entry. This means that users do not have to

spend much time learning how to enter a program, but rather they

can spend their time programming and solving the control problem.

Most PLCs are programmed using very similar instructions. The

only difference may be the mechanics associated with entering the

program into the PLC, which may vary from manufacturer to

manufacturer

The two basic types of programming devices are:

– Mini-programmers

– personal computers

Mini-ProgrammersMini-Programmers

Mini-Programmers Cont’d Mini-Programmers Cont’d

Mini-programmers, also known as handheld or manual

programmers, are an inexpensive and portable way to program

small PLCs (up to 128 I/O).

Mini-programmers can also be useful tools for starting up, changing,

and monitoring the control logic

Some mini-programmers offer removable memory cards or

modules, which store a complete program that can be reloaded at

any time into any member of the PLC family

Most mini-programmers are designed so that they are compatible

with two or more controllers in a product family

Personal ComputerPersonal ComputerCommon usage of the personal computer (PC)

in our daily lives has led to the practical

elimination of dedicated PLC programming

devices.

Due to the personal computer’s general-

purpose architecture and standard operating

system, most PLC manufacturers provide the

necessary PC software to implement ladder

program entry, editing, documentation, and

real-time monitoring of the PLC’s control

program.

Selecting a PLCSelecting a PLCNumber of logical inputs and outputsNumber of logical inputs and outputs

MemoryMemory

Number of special I/O modulesNumber of special I/O modules

Expansion CapabilitiesExpansion Capabilities

Scan TimeScan Time

CommunicationCommunication

SoftwareSoftware

SupportSupport

Dollars Dollars

Example of PLC SpecificationsExample of PLC Specifications

ManufacturesManufactures

OMRONOMRON

Allen BradleyAllen Bradley

Schneider (Modicon, Telemecanique, Square D)Schneider (Modicon, Telemecanique, Square D)

GE FanucGE Fanuc

SiemensSiemens

Automation Direct (Koyo)Automation Direct (Koyo)

ToshibaToshiba

MitsubishiMitsubishi

HitachiHitachi

Major BrandsMajor Brands

Programming PLC’sProgramming PLC’s

The purpose of a PLC Program is to The purpose of a PLC Program is to control the state of PLC control the state of PLC

outputs based on the current condition of PLC Inputsoutputs based on the current condition of PLC Inputs

A program is a connected series of instructions written in a

language that the PLC can understand.

There are three forms of program format:

– instruction: a word/mnemonic entry system

– Ladder: a graphical program construction method using a relay

logic symbols

– SFC (Sequential Function Chart) :a flow chart style of STL

(STep Ladder) program entry

Programming PLC’s Cont’dProgramming PLC’s Cont’d

Not all programming tools can work in all programming forms.

Generally hand held programming panels only work with

instruction format while most graphic programming tools will work

with both instruction and ladder format. Specialist programming

software will also allow SFC style programming.

Programming PLC’s Cont’dProgramming PLC’s Cont’d

Ladder Logic ConceptsLadder Logic Concepts

| | |/|

Read / Conditional Instructions

Write / Control Instructions

| | |/|

| | |/|

| |

| | |/| ( )

| |

( )

( )

( )

( )

| |

Start (Rung #1)

End (Rung #5)

Ladder Logic ConceptsLadder Logic ConceptsThe vertical line of the diagram represent the power The vertical line of the diagram represent the power railsrailsEach rung on the ladder defines one operation in Each rung on the ladder defines one operation in the control processthe control processLadder diagram is read from left to right and from Ladder diagram is read from left to right and from top to bottomtop to bottomEach rung must start with an input or inputs and Each rung must start with an input or inputs and must end with at least one outputmust end with at least one outputOne device can appear in more than one rung of One device can appear in more than one rung of ladder ladder Inputs and outputs are all identified by their address Inputs and outputs are all identified by their address the notation used depending on the plc manufacturethe notation used depending on the plc manufacture

Ladder Logic ConceptsLadder Logic Concepts

Advantages Of PLCAdvantages Of PLC

The advantages they offer are:The advantages they offer are:

– Cost effective for controlling complex systemsCost effective for controlling complex systems

– Flexible and can be reapplied to control other systems Flexible and can be reapplied to control other systems

quickly and easilyquickly and easily

– Trouble shooting aids make programming easier and Trouble shooting aids make programming easier and

reduce downtimereduce downtime

– Reliable components, ensure operation for yearsReliable components, ensure operation for years

– Variety of I/O interfacesVariety of I/O interfaces

– Small sizeSmall size

– Growing with technology, faster scan times, capability etcGrowing with technology, faster scan times, capability etc

– Quick I/O disconnects that aids in field servicingQuick I/O disconnects that aids in field servicing

– Software Timers/Counter, RelaysSoftware Timers/Counter, Relays

– Clean failure modeClean failure mode

– On-line programmingOn-line programming

– Availability of replacement partsAvailability of replacement parts

Advantages Of PLC Cont’dAdvantages Of PLC Cont’d

Input DevicesInput DevicesThe most common class of input interfaces is digital (or

discrete).

Discrete input interfaces connect digital field input

devices (those that send noncontinuous, fixed-variable

signals) to input modules of programmable controller.

The discrete, noncontinuous characteristic of digital input

interfaces limits them to sensing signals that have only two

states (ON/OFF, OPEN/CLOSED, TRUE/FALSE). To an

input interface circuit, discrete input devices are

essentially switches that are either open or closed,

signifying either 1 (ON) or 0 (OFF).

Input Devices Cont’dInput Devices Cont’d

Analog signals have an infinite number of states.

Temperature, for example, is an analog signal because it

continuously changes by infinitesimal amounts.

Consequently, a change from 70°F to 71°F is not just

one change of 1°F, but rather an infinite number of

smaller changes of a fraction of a degree.

Analog input modules digitize analog input signals,

thereby bringing analog information into the PLC

Mechanical SwitchMechanical SwitchThe mechanical switch generates an on/off signal or signals as a

result of some mechanical input causing the switch to open or

close

Switches are available with normally open (NO) or normally close

(NC)

NO contact has its contact open in the absence of a mechanical

input and the mechanical input is used to close the switch

NC contact has its contact closed in the absence of a mechanical

input and the mechanical input is used to open the switch

Mechanical Switch cont’dMechanical Switch cont’d

2.2. Limit switchLimit switch

1.1. On/Off switch (On/Off switch (Toggle switch)

Mechanical Switch cont’dMechanical Switch cont’d

3.3. Limit switchLimit switch

Proximity switchesProximity switches

Proximity sensors are discrete sensors that sense when an object has come near to the sensor face. There are four fundamental types of proximity sensors the inductive proximity sensor, the capacitive proximity sensor, the ultrasonic proximity sensor, and the optical proximity sensor.

Inductive Proximity Sensor

Inductive proximity sensors operate on the principle that

the inductance of a coil vary as a metallic (or

conductive) object is passed near to it. Because of this

operating principle, inductive proximity sensors are only

used for sensing metal objects. They will not work with

non-metallic materials.

Small diameter sensors (approximately ¼” in diameter)

have typical sensing ranges in the area of 1mm, while

large diameter sensors (approximately 3" in diameter)

have sensing ranges in the order of 50mm or more

Inductive Proximity Sensor cont’d

Capacitive Proximity Sensor

Capacitive proximity sensors are available in shapes and

sizes similar to the inductive proximity sensor

capacitive proximity sensors will sense both metallic and

non-metallic objects.

The principle of operation of the sensor is that an internal

oscillator will not oscillate until a target is moved close to

the sensor face. The target varies the capacitance of a

capacitor in the face of the sensor that is part of the

oscillator circuit.

The Ultrasonic Proximity Sensor

An ultrasonic “ping” is sent from the face of the sensor. If

a target is located in front of the sensor and is within

range, the ping will be reflected by the target and

returned to the sensor.

When an echo is returned, the sensor detects that a

target is present, and by measuring the time delay

between the transmitted ping and the returned echo, the

sensor can calculate the distance between the sensor

and the target.

The Ultrasonic Proximity Sensor

Optical Proximity Sensor

Optical sensors are an extremely popular method of providing discrete-output sensing of objects. Since the sensing method uses light, it is capable of sensing any objects that are opaque.

They operate over long distances (as opposed to inductive or capacitive proximity sensors), will sense in a vacuum (as opposed to ultrasonic sensors), and can sense any type of material no matter whether it is metallic or nonmetalic

Transmissive TypeTransmissive Type

Reflective TypeReflective Type

BenefitsBenefits

The benefits achieved with programmable The benefits achieved with programmable

controllers will grow with the individual using controllers will grow with the individual using

them: them:

““The more you learn about PLC’s, the more you The more you learn about PLC’s, the more you

will be able to solve other control problems.”will be able to solve other control problems.”

Thank you….Thank you….

Questions ?Questions ?

programmable logic controllers plc’s التحكم المنطقى المبرمج

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