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    PRACTICAL-1

    Aim: To study about terms and definitions of control valve.

    1. Control valve:-A control valve is the most commonly used final control element used to regular

    material flow in a process.

    2. Capacity:-Rate of flow through a valve under stated continues.

    3. Leakage:-Quantity of field passing through an assembled valve is in fully close position under

    stated closure forces with pressure differential and temperature as specified.

    4. Normally closed:-Applying to a normally closed control valve assembly one which closed. When the

    actuator pressure is reduced to atmospheric.

    5. Normally open:-Applying to a normally open control valve assembly one which open, When the

    actuatorpressure is reduced to atmospheric.

    6. Plug:-A moveable part which provide a variable restriction in a part.

    7. Rangeability:-The ratio of maximum to minimum usable sizing coefficient.

    8. Seat:-The portion of a seat ring of valve body which a valve plug contactos for closure.

    9. Stem:-A rod extending through the honnet assembly to permit positioning the valve plug.

    10.Trim:-

    The part of a valve which come in to control with the flowing fluid.

    11. Valve body:-

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    Practical-2

    Aim: to study about butterfly valve

    Butterfly valve:

    Construction:

    Figure shows the diagram of butterfly valve. Construction of these valve is simple as shown in figure. The valve consists of a single disc or vane rotating inside a circular or rectangular

    pipe, as shown in figure.

    Operation: The most outstanding feature of tight closing. The butterfly valve, the flow leakage

    at the full valve closer is very small.

    The valve has an eccentric valve vane and a teflon seat and it is used for control oflarge volume low pressure flow.

    Range ability of these type of valve is 5 to 15. Uses: These valves are used for control of air and gas flow.

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    They can be used for liquid flow also if the pressure differential is not large. Advantages: Low cost. High capacity. Available in large size. Require minimum space for installation.

    Disadvantages: Operating torque can be high. Tight shut off is depend on use of resilient seats which are temp. liquid.

    EXERCISE QUESTIONS:

    1) WHAT ARE THE MAIN USES OF BUTTERFLY VALVE?

    2) WRITE ADVANTAGES AND DISADVANTAGES OF BUTTERFLY VALVE.

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    PRACTICAL- 3

    Aim: To study about diaphragm valve.

    Diaphragm valve:

    Construction:-

    The main components of the diaphragm type valve are a cylindrical body there is

    bonnet. It house a circular, flexible diaphragm ,comparison element and a stem. The stem can

    be moved up or down by threaded screw arrangement operated by a circular ring-shaped

    lever at the top.

    Working:-

    The top lever clockwise the stem is brought down. In the lowermost position of stem

    the diaphragm is pressed downward. It becomes straight in horizontal plane. Fully touches

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    the valve seat and blocks the opening between inlet and outlet fluid lines. It is fully closed

    position.

    It the types the working parts are physically isolated from the process fluids. So,

    diaphragm work as closure element provides isolated and sealing against leakage of fluid.

    The valve is simple, easy to operate and maintain.

    It is very useful in chemical and fertilizer industries and water treatment plants for

    low temperature and pressure application of liquid flow control. Due to isolation provided by

    diaphragm it is suitable for corrosive liquids also.

    Advantages: High capacity. Low cost.

    Good for slurry services. Self cleaning action. Provide tight shut off if pressure is low. Disadvantages: Poor control characteristics. Short diaphragm life. Low range ability. Slow response speed.Not suitable for high pressure drop applications.

    EXERCISE QUESTIONS:

    1) WRITE MARITS AND DEMARITS OF DIAPHRAGM VALVE.2) WHAT ARE THE MAIN PARTS OF DIAPHRAGM VALVE?

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    Practical-4

    Aim: To study about Solenoid valve.

    Solenoid valve:

    Construction: Figure shows the diagram of solenoid valve. Solenoid valve is a combination of two basic functions, in which a solenoid coil

    with its plunger as an actuator and operating on the electromagnetic principle.

    Valve containing an orifice in which disc or plug is positioned to restrict or allowthe flow.

    The valve is opened or closed by the movement of the magnetic plunger which isdown in to the solenoid

    Operation: The fully automatic valve operates when current is applied to the solenoid and

    automatically return to its original position when the current is cut off.

    These valves are available in normally open (NO) or normally close (NC) design. The NC valve will open when the current is applied to the solenoid and will close

    when current is cut off. The NO valve will close when current is applied and opens when current is cut off. These valves are often called magnetic valves.

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    Applications: They are widely used for emergency shut off services or for automatic opening of a

    valve simultaneous with the operation of a pump or other piece of equipment.

    It is the best to keep automatic control applications to large capacity system such ascontrol of liquid level in strong tanks.

    Uses: These valves are used for control of air and gas flow. They can be used for liquid flow also if the pressure differential is not large.

    Advantages:

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    Low cost. High capacity. Available in large size. Require minimum space for installation.

    Disadvantages: Operating torque can be high.

    Tight shut off is depend on use of resilient seats which are temp. liquid.

    EXERCISE QUESTIONS:

    1) WRITE APPLICATIONS OF SOLENOID VALVE.

    2) WRITE MERITS AND DEMARITS OF SOLENOID VALVE.

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    PRACTICAL5

    AIM:- TO STUDY DIFFERENT VALVE ACTUATORS.

    THEORY:-

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    It translates the output signal of controller into sufficient power & motion to operate

    the final control element. The actuator may obtain required to employ a power amplify

    mechanism. There are different types of actuators.

    Electric actuators1. motor actuator2. solenoid actuator

    Pneumatic actuator1. diaphragm & spring type / spring less2. piston and cylinder type

    Hydraulic actuator

    Electro pneumatic actuators.

    1) Electric actuator:-

    Electric actuators are employed to provide a position output to an inputelectric signal.

    The relay type electric actuator is shown in figure. A low inertia reversible at motor drives the output through gear. A mechanical feedback is employed such that a rotation at the output rotates

    lever acting in a feedback spr.

    Increase in DC current at the input coil causes force to act on the balancebeam & pulls the beam down, thus making the upper contact.

    This drives the motor in on direction so that the output rotates, there by pullingon the spring & rebalancing the vane coil.

    Armature output position is therefore proportional to an input current. The power amplifier may be inserted between the balance beam and motor. So

    that contacts do not have to carry large current.

    The amplifier may be actuated by a differential transformer or an oscillatorcoil on the balance bear.

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    2)Pneumatic actuator:-

    Pneumatic actuator may operate directly from the pneumatic output signalfrom a pneumatic controller or they may employ a separate source ofcompressed air.

    There are five common methods of operation of pneumatic valve actuators. Spring actuator Spring actuator with positioner Spring less actuator Piston actuator Electro pneumatic actuator.

    i. Spring actuator:-

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    A spring actuator operates directly from the air pressure output of a pneumaticcontroller in order to provide an output position proportional to the input air pressure.

    The diaphragm to make of fabric base rubber & supported by a backing plate. The input air pressure acts against the diaphragm & causes a downward force which

    compressed the spring.

    A static balance the force of the air pressure against the diaphragm equals the springcompression factor.

    The standard input operating range of spring actuator is 3-15 psi.

    Spring actuator with positioner:-

    Actuator often requires positioner when static friction forces are large orwhen the response of the motor is too slow.

    The positioner consists of an input bellows, a nozzle & amplifying pilot &the feedback levers & spring.

    When the input air pressure increases the input bellows move to the right andcauses the baffle to cover the nozzle. The change of nozzle back pressure is

    amplified by the pilot and transmitted to the diaphragm.

    The diaphragm moves down and the feedback lever compress the spring toreturn the baffle to a balance position.

    The use of the positioner results good performance in such a way Linearity is improved and hysterises is reduced.

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    Actuated can handle much higher static friction forces because of theamplifying pilot.

    Variable thrust forces on the motor stem do not disturb the stemposition to any great extent.

    Speed of response is generally improved.

    3. Spring less actuator:-

    The actuator with a spring positioner does not improve the ability of the actuator tohandle large inertia or thrust forces.

    Spring less actuator is useful for large thrust forces. The input pressure of 10 to 100 is required. Assume that the calion regulator is set to provide 9 psig. Pressure on the underside

    of the diaphragm.

    At static balance and no thrust forces on the actuator stem upper side pressure mustbe of 9 psig.

    If the input pressure increases and the upperside pressure is raised to a high value,the actuator stem then moves downward as the actuator stem attains the new

    position. This is generally from 3-10 times the thrust forces handling by a handled

    by spring actuator with or without positioner.

    Piston actuator:-

    The piston actuator is operated employed for larger thrust forces that can be handledby the single acting actuator and the piston is used in order to obtain long stroke.

    The pilot is generally a spool type diverting valve and requires an air supply of 30-100 psig.

    When pressure is applied, the bellows moves to the right and pushes the pilot spoolupward.

    This action opens the upper side of the cylinder to the air supply and opens the lowerside to atmosphere.

    Thus the action is to return to the neutral position. Thus the positioner of piston is proportional to the input pressure.

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    3.Electropneumatic actuator:-

    If a suitable air supply is available, a pneumatic actuator can provide verylarge power output and may be operated directly from an electric control

    system.

    This requires transducing the electrical output of a controller into an inputvariable for the actuator.

    The input electric signal enters the voice coil. The input coil is supported infield of a permanent magnet. So that the coil attends the force proportional to

    the magnitude of the input D.C. current.

    The force causes the deflection of balance beam covers the nozzle and resultspressure acts on the feedback bellows to cause a frequency on the balance

    beam equal but opposite to that of the voice coil.

    The output pressure is proportional to input D.C. current. The electro pneumatic actuator combines the voice coil and pilot in the

    positions of a pneumatic actuator.

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    EXERCISE QUESTIONS:

    1) LIST TYPES OF ACTUATORS.

    2) WHAT IS THE MAIN FUNCTION OF ACTUATORS?

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    PRACTICAL-6

    AIM : TO STUDY ABOUT VALVE POSITIONERS.

    VALVE POSITIONERS

    A Valve positioner is basically a relay that senses both an instrument signal and a valve

    stem position. The primary function is to ensure that the valve plug position is always

    directly proportional to its controller output pressure.

    For example,if the positioner receives a 35% signal,it will Supply sufficient pressure to

    the actuator to cause it to stroke 35% of its travel. Effectively it may bedescribed as a

    Closedloop controller that has the instrument signal as I/p,An output to the valvediaphragm and feedback from the

    TYPES OF VALVE POSITIONERS

    Pneumatic types valve positioners1. Motion balance type2. Force balance type3. Built-in type Electropneumatic type valve positioner

    1. Pneumatic type valve positionerThere are many valve positioners available, but two basic desing approaches have been

    made; motion balance

    and fource balance. Positioners usually are mounted on the side of diaphragm actuators.

    They are mecahanically connected to the valve stem or piston so that the stem piston can

    be compared with the pition dictated by the controller. Typical designs are show and

    described.

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    a. Motion balance type positionerfigure shows a schematic of a motion balance positioner and its physical appearance is

    seen in figure. It consists basically of a bellows to receive the instrument signal, a beam

    fixed to the bellows at one end and, through linkage, to the valve stem at the other end ,

    and a relay whose nozzle froms a fiapper-nozzie arrangement with the beam. As the

    bellows moves in response to a changed instrument signal, the flapper-nozzle arrange-

    ment moves, either admitting air to, or bleeding air from,

    the diaphragm until the valve stem position corresponds to the instrument air signal, At

    this point the positioner is once again in equilibrium with the changed instrument signal.

    b. Motion balance pneumatic positioner

    Motion balance pneumatic positioner with outside cover removed

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    c. Force balance type positionerA force positioner is show in figure. The output pre-ssure from a controller is applied to

    the bellows of the positioner. For any given controller output, there is a corresponding

    position of the controlled element (in this case ,a cylinder). At the slightest change in

    signal pressure, full supply pressure is available to ensure immediate and accurate

    positioning of the cylinder.

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    2. ELECTROPNEUMATICUse of electronic control loops with air-operated valves has led to the development of

    electropneumatic positioners, a combination of an electronic-to-air transducer and a

    positioner. This is a force balance device and is supplied as direct or reverse acting. With

    direct action (increasing electrical input signal increases the air output pressure), an

    increase of the input signal causes the coil to produce a force on the beam, moving the

    flapper to cover the nozzle. The increase in nozzle back pressure causes the relay plug to

    close the exhaust in the diaphragm block and open the inlet, increasing positioner output

    pressure to the control valve actuator. the resuitant valve stem motion extends the spring

    (through linkage) until the spring force is balanced by the coil force. As they equalize, thenozzle back pressure decreases, allowing the relay plug to close the inlet and open the

    exhaust. The system is in equilibrium, and the positioner output is stabilized at a value

    necessary to maintain the required plug position.

    ELECTROPNEUMATIC POSITIONNER SCHEMATIC DIAGRAM

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    Mounting of valve positioner:

    Application of valve positioners:

    Single port valve handling high pressure drop that require large stem thrusts Valve handling viscous fluids, sludege or solids in suspension. When increased speed at operation is required. Split rang operation when two or more control valves are operated by a single

    controller

    On three-way control valves On application where valve packing is usually tight. Where control valve is located at a grate distance from controller.

    EXERCISE QUESTION:

    1) GIVE THE CLASSIFICATION OF VALVE POSITIONERS.2) WRITE THE APPLICATIONS OF VALVE POSITIONERS.

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    PRACTICAL: 7

    AIM: TO STUDY THE CHARACTERISTICS OF CONTROL VALVE.

    THEORY:

    CHARACTERISTICS OF CONTROL VALVE:

    The performance of the control valve is known from the few characteristics of valve,

    where characteristics of the control valve flow is the relationship between the valve plug position

    and flow through the valve.

    There are three types of characteristics of control valve:

    1) Quick opening2) linear3) equal percentage

    GRAPHICAL REPRESENTATION OF CHARACTERISTICS OF CONTROL

    VALVE.

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    (1) QUICK OPENING:

    o Quick opening provide for a maximum change in flow rate of low steam travel whilemaintaining a linear relationship through the most of the steam travel of capacity is

    obtained at 90% of the valve capacity is obtained at 30% valve opening, and the straight

    line relationship exists to that point.o This type of valve plugs is used primarily for ON-OFF services or in regulators.o They are also suitable for systems with constant pressure drop where linear characteristics

    are needed.

    (2) LINEAR:

    o This type of flow characteristics produces flow directly proportional to the valve lift. Forexample, 50% of valve lift produces 50% of valve flow.

    o This proportional relationship produces a constant slope so that each incremental changein valve plug position produces alike incremental change in flow.

    o If the pressure drop is constant, characteristics are as shown in figure.o These types of valve plugs are used for liquid level control and for control applications

    requiring constant gain.

    (3) EQUAL PERCENTAGE:

    o In this type, equal increment of steam travel produces equal percentage changes in existingflow.

    oThe change is always proportional to the quantity flowing before the change.oThis type of plugs is used in pressure control applications where only a small percentage ofthe system drop is available for the control valve.

    EXERCISE QUESTIONS:

    1) DRAW THE CHARECTERISTICS OF CONTROL VALVE.2) WRITE ABOUT QUICK OPENING.

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    PRACTICAL- 8

    AIM: TO STUDY ABOUT VALVE NOISE.

    Theory:-

    In industrial environment the running machinery may generate a lot of noise. The

    control valves generate a considerable amount of noise is some cases. The control valve may

    be dealing with liquid, gases or vapour. In the process of fluid flow there is a lot of variation

    in the fluid velocity and pressure. Usually the velocity and pressure change may be associated

    with generation of noise with control valves generating the noise, noise due to cavitation andaerodynamic noise.

    Mechanical vibration:-

    Sometimes the valve components resonate at natural frequency of vibration. But,

    noise is only a symptom indicating development of vibrations. When the mechanical

    components vibrate at high frequency for a long time there may be a fatigue failure of the

    component.

    Hydraulic noise:-

    Just like mechanical vibrations and mechanical noise the other source of problem is

    hydraulic noise. The control valve deal with fluid flow. When liquid flow takes place through

    obstruction create by the valve there is a change of velocity.

    Aerodynamic noise:-

    The actual liquid flow is turbine rather than laminar. The high velocity fluid passing

    through the valve obstruction has vena contract on the downstream side. Generation of vapor

    creates mixed phase of flow. It results in high velocity turbulence and in small cells pressure

    shocks are developed.

    EXERCISE QUESTIONS:

    1) WHAT IS VALVE NOISE?

    2) WHAT ARE THE CAUSES OF VALVE NOISE?

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    Practical-9

    AIM: TO STUDY ABOUT AC TACHOMETER.

    THEORY:

    What is TACHOMETER?

    A Tachometer or rate generator is an electromechanical device that convertsmechanical angular velocity (speed) into proportional output voltage.

    This device may be designed for any unit that can be converted into a function ofrotational motion, such as rpm, km/hour etc.

    Tachometer is used as a transducer for speed, it is also called speedometer.Requirements of a good Tachometer:

    Linearity: The o/p voltage should vary linearly with the speed. Sensitivity: More o/p voltage should be available for small change in the speed. Magnitude of the o/p voltage should be same in both the directions of rotations. The o/p voltage should be free from undesirable disturbances like noise, harmonics,

    ripple etc.

    A.C. TACHOMETER

    Working Principle:

    When the two windings are placed 90.

    apart and one winding is excited through the a.c.

    source, no e.m.f. is induced in the other winding. But when the flux is linked through the

    short circuited rotor, e.m.f. is induced in the rotor winding which is proportional to the speed

    of the rotor.

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    CONSTRUCTION:

    It comprises of two main parts: (1) stator (2) rotor. The stator consists of laminated core, which has slots cut on to its inside periphery. The slots carry two windings placed 90. apart. One winding is excited from the a.c. source & is called the exciting winding. The other winding is called the o/p winding. The rotor is either of squirrel cage type or drag cup type. Here is the squirrel cage type rotor as shown in fig.

    In squirrel cage type rotor aluminum bars are embedded in the laminated core. These bars are short circuited with the help of two short circuiting rings. In drag cup type an aluminum die cast rotor in the shape of a cup is used. In this type the weight of the rotor is reduced.

    WORKING:

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    In a.c. tachometer, an alternating supply signal fed into its exciting winding, thealternating flux is produced & hence an e.m.f. is induced in its quadrature winding.

    When the rotor shaft is stationary & the primary (exciting) winding is excited by ana.c. input voltage, the induced voltage in the secondary (o/p) winding is zero, due to

    the relative positions of the two windings being placed 90

    .

    to each other. As the rotor shaft rotates, a voltage is induced in the secondary (o/p) winding whosemagnitude is directly proportional to the rotor shaft speed and the frequency is same

    as that of the primary (exciting) voltage.

    The o/p voltage is in the phase with the exciting voltage. Change in the direction of rotation of the rotor shaft causes a 180. phase shift of the

    o/p voltage.

    A positive direction of rotation of the rotor shaft is such that its o/p voltage is in phasewith the exciting voltage.

    The polarity of the voltage depends upon the direction of the o/p rotation. The o/p voltage e(t) can be expressed as

    =

    d(t)

    Where K= tachometer constant

    = angular velocity

    d(t)

    The lap lace transform of this equn. Will be

    So the transfer function will be

    E (s) = Ks

    Since the o/p signal is a voltage, a high i/p resistance is connected with the readoutinstrument to give near zero current flow in the secondary winding as shown in fig.

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    Any current flow in the o/p winding will cause a voltage drop which will besubtracted from the measured voltage and thus give the error in the speed

    measurement.

    With this type of tachometer, speed in the range of 500 to 10,000 rpm may bemeasured.

    Advantages:

    i. Output is ripple free.ii. Reduced maintenance.

    iii. Less driving torque is needed, due to the reduced friction.Disadvantages:

    i. More voltages are not possible to produced.So sensitivity is not high compared to that of D.C. type Tachometer.

    Application:

    i. As speed measuring and speed sensing devices.ii. As electromechanical integrator in analog computers.

    iii. In automatic control system.iv. As position controlling device in feedback.

    EXERCISE QUESTIONS:

    1) WHAT IS TACHOMETER?

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    2) WRITE THE APPLICATIONS OF TACHOMETER.

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    Practical:-10

    Aim: to study about construction and working of servo motors & its characteristics.

    Theory:

    SERVOMOTORS:-

    Servomotors are available as A.C or D.C motors. Early servomotors were generally D.C

    motors because the only type of control for large currents was through SCRs for many years.

    As transistors became capable of controlling larger currents and switching the large currents

    at higher frequencies, the A.C servomotor became used more often. Early servomotors were

    specifically designed for servo amplifiers. Today a class of motors is designed for

    applications that may use a servo amplifier or a variable frequency controller, which means

    that a motor may be used in a servo system in one application, and used in a variable

    frequency drive in another application. Some companies also call any closed loop system that

    does not use a stepper motor a servo system, so it is possible for a simple A.C inductionmotor that is connected to a velocity controller to be called a servomotor.

    Servomotors can be classified into two parts:-

    1. A.C servomotors.2. D.C servomotors.A.C SERVOMOTORS:-

    PRINCIPLE:-

    When a 2 phase winding is evicted from a 2 phase supply, rotating magnetic field is

    produced. If a closed coil is placed in the field, current is induced in the coil and a toque is

    produced on the coil due to which it rotates.

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    CONSTRUCTION:-

    1. It consists of a stator & rotor. Stator comprises of a laminated core with slots cut on theinside periphery. Two phase winding is the reference winding and excited from the ac

    voltage. Another winding is called the fixed AC voltage. It is made into two sections.

    These two connected either in series or in winding to produce a 90 degree phasedisplacement to produce a 2 phase supply from the single phase supply.

    2. The rotor is of squirrel cage type. The rotor bars are of aluminium. These are shortcircuited at the two ends by short circuiting rings.

    WORKING:-

    When the motor windings are excited, rotating magnetic field is produced due to the 2

    phase supply, produced due to split phasing. This induces e.m.f. in the rotor bars. As the bars

    are short circuited current is circulated. Due to interaction of the flux and the current, torque

    is produced and the rotor starts rotating in the direction of the rotating field. The direction of

    rotation can be reversed when the phase of the control voltage is reversed i.e. by reversing the

    connections of the control winding. The speed depends on the magnitude of the controlvoltage.

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    CHARACTERISTICS:-

    The torque speed characteristics of a conventional induction motors are shown in figure.

    1. Figure (a) it is seen that as the rotor resistance is increased, the characteristic becomes

    almost linear.

    2. Figure (b) shows the characteristics of the 2 phase servomotor in which the rotor bars used

    are of high resistance. Different curves are for different control voltage. The characteristic is

    linear in the low speed region.

    ADVANTAGES:-

    1. It has low inertia due to the reduced weight of the rotor. So it can be started and stoppedquickly.

    2. Reduced maintenance as there are no brushes, commutator etc.DISADVANTAGES:-

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    1. Less output power for the same size of the motor as compared to D.C. motor.2. Characteristic is not very much linear as compared to D.C. motor.APPLICATION:-

    1. AC servomotors are used as control elements in A.C. servo systems.2. These motors are not designed to supply large power. The rating is up to 100W. These are

    designed for frequencies of 50, 60,400, and 1000 Hz.

    Higher frequencies are used to reduce the size.

    EXERCISE QUESTIONS:

    1) WRITE THE WORKING PRINCIPLE OF AC SERVOMOTOR2) WRITE APPLICATIONS OF AC SERVOMOTOR.3) WRITE THE CARECTERISTICS OF AC SERVOMOTOR.

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    PRACTICAL:-11

    AIM:- TO STUDY ABOUT STEPPER MOTOR.

    THEORY:

    Principle of stepper motor:

    There are many kind of stepper motors.

    Unipolar type, Bipolar type, Single-phasetype, Multi-phase type... Single-phase stepper

    motor is often used for quartz watch.

    On this page, I will explain the operation

    principle of the 2-phase unipolar PM type

    stepper motor.

    In the PM type stepper motor, a permanent

    magnet is used for rotor and coils are put on stator. The stepper motor model which has 4-

    poles is shown in the figure on the left. In case of this motor, step angle of the rotor is 90

    degrees.

    As for four poles, the top and the bottom and either side are a pair. coil, coil and coil,

    coil correspond respectively. For example, coil and coil are put to the upper and lower

    pole. coil and coil are rolled up for the direction of the pole to become opposite when

    applying an electric current to the coil and applying an electric current to the coil. It is

    similar about and , too.

    The turn of the motor is controlled by the electric current which pours into , , and .

    The rotor rotational speed and the direction of the turn can be controlled by this control.

    Different details of configuration have to be decided when choosing a motor. Almosteverything is combineable

    A stepper motor is abrushless, synchronouselectric motorthat can divide a full rotation into

    a large number of steps, for example, 200 steps. When commutated electronically, the motor's

    position can be controlled precisely, without any feedback mechanism (seeopen loop

    control).

    http://en.wikipedia.org/wiki/Brushless_DC_electric_motorhttp://en.wikipedia.org/wiki/Brushless_DC_electric_motorhttp://en.wikipedia.org/wiki/Brushless_DC_electric_motorhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Open_loophttp://en.wikipedia.org/wiki/Open_loophttp://en.wikipedia.org/wiki/Open_loophttp://en.wikipedia.org/wiki/Open_loophttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Brushless_DC_electric_motor
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    A stepper motor's design is virtually identical to that of a low-speed synchronous AC motor.

    In that application, the motor is driven with two phase AC, one phase usually derived through

    a phase shifting capacitor. Another similar motor is theswitched reluctance motor, which is a

    very large stepping motor with a reduced pole count, and generally closed-loop commutated.

    Stepper Motor Characteristics

    A stepper motor generates excellent torque at low speed, and falls rapidly as it speeds up. The

    torque curve may be extended by using current limiting drivers and increasing the driving

    voltage -- the best performing drive systems use line voltages.

    Steppers exhibit more vibration than other motor types, as the discrete step tends to snap the

    rotor from one position to another. This vibration can become very bad at some speeds, and

    can cause the motor to lose torque. The effect can be mitigated by accelerating quickly

    through the problem speed range, physically dampening the system, or using a micro-

    stepping driver. Motors with greater number of phases also exhibit smoother operation than

    those with less phases.

    Fundamentals of Operation

    A normalDC motoris commutated internally and generates torque when a voltage is

    impressed across its two terminals. Stepper motors, on the other hand, have multiple winding

    phases, typically two but could be three or five, which require external commutation. The

    number of terminals, or wires going to the motor, varies depending on it's internal circuit and

    the number of winding phases, but is typically four or more.

    The motor stator features multiple "toothed"electromagnetpoles. Having the poles toothedgreatly increases the effective number of magnetic poles in the motor. The rotor is also

    toothed, and is magnetically polarized throughreluctanceor containspermanent magnets. To

    make the rotor turn one full step, the current in one of the winding phases is reversed (which

    one will determine the direction). To move the rotor continuously, the winding phases are

    reversed alternately.

    If we consider a two phase stepper motor, the net effect of activating each winding is to

    produce a torque that draws the rotor teeth into a position between two stator poles. When a

    stator pole's polarity is switched, a rotor pole moves into a new equilibrium position on the

    other side of an unswitched stator pole. Each of those slight rotations is called a full step.

    It should be observed that the equilibrium positions occur every 4 full steps, so that if a motor

    is driven too hard, it will slip, orlose steps, in multiples of 4.

    Open Loop vs. Closed Loop Commutation

    Steppers are generally commutated open loop, ie. the driver has no feedback on where the

    rotor actually is. Stepper motor systems must thus generally be over engineered, especially if

    the load inertia is high, or there is widely varying load, so that there is no possibility that the

    motor will lose steps. This has often caused the system designer to consider the trade-offs

    between a closely sized but expensive servo system and an oversized but relatively cheap

    stepper.A new development in stepper control is to incorporate a rotor position feedback (eg.an encoder or resolver), so that the commutation can be made optimal for torque generation

    http://en.wikipedia.org/wiki/Reluctance_motorhttp://en.wikipedia.org/wiki/Reluctance_motorhttp://en.wikipedia.org/wiki/Reluctance_motorhttp://en.wikipedia.org/wiki/Electric_motor#DC_motorshttp://en.wikipedia.org/wiki/Electric_motor#DC_motorshttp://en.wikipedia.org/wiki/Electric_motor#DC_motorshttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Reluctancehttp://en.wikipedia.org/wiki/Reluctancehttp://en.wikipedia.org/wiki/Reluctancehttp://en.wikipedia.org/wiki/Permanent_magnethttp://en.wikipedia.org/wiki/Permanent_magnethttp://en.wikipedia.org/wiki/Permanent_magnethttp://en.wikipedia.org/wiki/Permanent_magnethttp://en.wikipedia.org/wiki/Reluctancehttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Electric_motor#DC_motorshttp://en.wikipedia.org/wiki/Reluctance_motor
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    according to actual rotor position. This turns the stepper motor into a high pole count

    brushless servo motor, with exceptional low speed torque and position resolution. An

    advance on this technique is to normally run the motor in open loop mode, and only enter

    closed loop mode if the rotor position error becomes too large -- this will allow the system to

    avoid hunting or oscillating, a common servo problem.

    Two Phase Stepper Motors

    There are two basic winding arrangements for the electromagnetic coils in a two phase

    stepper motor: bipolar and unipolar.

    Unipolar motors

    A unipolar stepper motor has logically two windings per phase, one for each direction of

    current. Since in this arrangement a magnetic pole can be reversed without switching the

    direction of current, the commutation circuit can be made very simple (eg. a single transistor)

    for each winding. Typically, given a phase, one end of each winding is made common: givingthree leads per phase and six leads for a typical two phase motor. Often, these two phase

    commons are internally joined, so the motor has only five leads.

    Amicrocontrolleror stepper motor controller can be used to activate the drive transistors in

    the right order, and this ease of operation makes unipolar motors popular with hobbyists; theyare probably the cheapest way to get precise angular movements.

    (For the experimenter, one way to distinguish common wire from a coil-end wire is by

    measuring the resistance. Resistance between common wire and coil-end wire is always half

    of what it is between coil-end and coil-end wires. This is due to the fact that there is actually

    twice the length of coil between the ends and only half from center (common wire) to theend.)

    A six lead unipolar motor may be driven by a bipolar driver. In this case, one of the windings

    on each phase is wasted as it never carries current.

    Bipolar motor

    Bipolar motors have logically a single winding per phase. The current in a winding needs to

    be reversed in order to reverse a magnetic pole, so the driving circuit must be more

    complicated, typically with anH-bridgearrangement. There are two leads per phase, none are

    common.

    http://en.wikipedia.org/wiki/Microcontrollerhttp://en.wikipedia.org/wiki/Microcontrollerhttp://en.wikipedia.org/wiki/Microcontrollerhttp://en.wikipedia.org/wiki/H-bridgehttp://en.wikipedia.org/wiki/H-bridgehttp://en.wikipedia.org/wiki/H-bridgehttp://en.wikipedia.org/wiki/H-bridgehttp://en.wikipedia.org/wiki/Microcontroller
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    Because windings are better utilised, they are more powerful than a unipolar motor of the

    same weight.

    8 Lead Stepper

    An 8 lead stepper is wound like a unipolar stepper, but the leads are not joined to common

    internally to the motor. This kind of motor can be wired in several configurations:

    Unipolar. Bipolar with series windings. This gives higher inductance but lower current per

    winding.

    Bipolar with parallel windings. This requires higher current but can perform better asthe winding inductance is reduced.

    Bipolar with a single winding per phase. This method will run the motor on only halfthe available windings, which will reduce the available low speed torque but require

    less current.

    Applications

    Computer-controlled stepper motors are one of the most versatile forms ofpositioning

    systems. They are typically digitally controlled as part of anopen loopsystem, and are

    simpler and more rugged thanclosed loopservosystems.

    Stepper motors are used in floppy disk drives, flatbed scanners, printers, plotters and many

    more devices. Note thathard drivesno longer use stepper motors to position the read/write

    heads, instead utilising avoice coiland servo feedback for head positioning.

    Stepper motors can also be used for positioning of valve pilot stages, for fluid control

    systems.

    EXERCISE QUESTIONS:

    1) WRITE WORKING PRINCIPAL OF STEPPER MOTOR.

    2) WRITE THE APPLICATIONS OF STEPPER MOTOR.

    http://en.wikipedia.org/wiki/Positioning_systemhttp://en.wikipedia.org/wiki/Positioning_systemhttp://en.wikipedia.org/wiki/Positioning_systemhttp://en.wikipedia.org/wiki/Positioning_systemhttp://en.wikipedia.org/wiki/Open_loophttp://en.wikipedia.org/wiki/Open_loophttp://en.wikipedia.org/wiki/Open_loophttp://en.wikipedia.org/wiki/Closed_loophttp://en.wikipedia.org/wiki/Closed_loophttp://en.wikipedia.org/wiki/Servohttp://en.wikipedia.org/wiki/Servohttp://en.wikipedia.org/wiki/Servohttp://en.wikipedia.org/wiki/Hard_drivehttp://en.wikipedia.org/wiki/Hard_drivehttp://en.wikipedia.org/wiki/Hard_drivehttp://en.wikipedia.org/wiki/Voice_coilhttp://en.wikipedia.org/wiki/Voice_coilhttp://en.wikipedia.org/wiki/Voice_coilhttp://en.wikipedia.org/wiki/Voice_coilhttp://en.wikipedia.org/wiki/Hard_drivehttp://en.wikipedia.org/wiki/Servohttp://en.wikipedia.org/wiki/Closed_loophttp://en.wikipedia.org/wiki/Open_loophttp://en.wikipedia.org/wiki/Positioning_systemhttp://en.wikipedia.org/wiki/Positioning_system
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    Practical-12

    AIM: TO STUDY ABOUT GYROSCOPE.

    Theory :-

    GYROSCOPE:

    A gyroscope is a device for measuring or maintainingorientation, based on the principle of

    conservation ofangular momentum. The essence of the device is a spinningwheelon anaxle.

    The device, once spinning, tends to resist changes to its orientation due to the angular

    momentum of the wheel. Inphysicsthis phenomenon is also known as gyroscopicinertiaor

    rigidity in space.

    Description and diagram

    http://en.wikipedia.org/wiki/Orientation_%28rigid_body%29http://en.wikipedia.org/wiki/Orientation_%28rigid_body%29http://en.wikipedia.org/wiki/Orientation_%28rigid_body%29http://en.wikipedia.org/wiki/Angular_momentumhttp://en.wikipedia.org/wiki/Angular_momentumhttp://en.wikipedia.org/wiki/Angular_momentumhttp://en.wikipedia.org/wiki/Wheelhttp://en.wikipedia.org/wiki/Wheelhttp://en.wikipedia.org/wiki/Wheelhttp://en.wikipedia.org/wiki/Axlehttp://en.wikipedia.org/wiki/Axlehttp://en.wikipedia.org/wiki/Axlehttp://en.wikipedia.org/wiki/Physicshttp://en.wikipedia.org/wiki/Physicshttp://en.wikipedia.org/wiki/Physicshttp://en.wikipedia.org/wiki/Inertiahttp://en.wikipedia.org/wiki/Inertiahttp://en.wikipedia.org/wiki/Inertiahttp://en.wikipedia.org/wiki/Image:Gyroscope_wheel-text.pnghttp://en.wikipedia.org/wiki/Image:3D_Gyroscope.pnghttp://en.wikipedia.org/wiki/Image:Gyroscope_wheel-text.pnghttp://en.wikipedia.org/wiki/Image:3D_Gyroscope.pnghttp://en.wikipedia.org/wiki/Inertiahttp://en.wikipedia.org/wiki/Physicshttp://en.wikipedia.org/wiki/Axlehttp://en.wikipedia.org/wiki/Wheelhttp://en.wikipedia.org/wiki/Angular_momentumhttp://en.wikipedia.org/wiki/Orientation_%28rigid_body%29
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    Diagram of a gyro wheel. Reaction arrows about the output axis (blue) correspond to forces

    applied about the input axis (green), and vice versa.

    Within mechanical combinations or devices constituting portions of machines, a conventional

    gyroscope is a mechanism comprising arotorjournaled to spin about oneaxis, thejournalsof

    the rotor being mounted in an inner gimbal or ring, the inner gimbal being journaled for

    oscillation in an outer gimbal which in turn is journaled for oscillation relative to a support.

    The outer gimbal or ring is mounted so as to pivot about an axis in its own plane determined

    by the support. The outer gimbal possesses one degree of rotational freedom and its axis

    possesses none. The inner gimbal is mounted in the outer gimbal so as to pivot about an axis

    in its own plane, which axis is alwaysperpendicularto the pivotal axis of the outer gimbal.

    Theaxleof the spinning wheel defines the spin axis. The inner gimbal possesses two degrees

    of rotational freedom and its axis possesses one. The rotor is journaled to spin about an axis

    which is always perpendicular to the axis of the inner gimbal. Hence the rotor possesses three

    degrees of rotational freedom and its axis possesses two. The wheel responds to a force

    applied about the input axis by a reaction force about the output axis. The 3 axes are

    perpendicular, and this cross-axis response is the simple essence of the gyroscopic effect.

    The behaviour of a gyroscope can be most easily appreciated by consideration of the front

    wheel of a bicycle. If the wheel is leaned away from the vertical so that the top of the wheel

    moves to the left, the forward rim of the wheel also turns to the left. In other words, rotation

    on one axis of the turning wheel produces rotation of the third axis.

    A gyroscope flywheel will roll or resist about the output axis depending upon whether the

    outputgimbalsare of a free- or fixed- configuration. Examples of some free-output-gimbal

    devices would be the attitude reference gyroscopes used to sense or measure the pitch, roll

    andyawattitude angles in a spacecraft or aircraft.

    a gyro wheel in action

    The center of gravity of the rotor can be in a fixed position. The rotor simultaneously spins

    about one axis and is capable of oscillating about the two other axes, and thus, except for its

    inherent resistance due to rotor spin, it is free to turn in any direction about the fixed point.

    Some gyroscopes have mechanical equivalents substituted for one or more of the elements,

    e.g., the spinning rotor may be suspended in a fluid, instead of being pivotally mounted in

    http://en.wiktionary.org/wiki/rotorhttp://en.wiktionary.org/wiki/rotorhttp://en.wiktionary.org/wiki/rotorhttp://en.wikipedia.org/wiki/Coordinate_axishttp://en.wikipedia.org/wiki/Coordinate_axishttp://en.wikipedia.org/wiki/Coordinate_axishttp://en.wikipedia.org/wiki/Journal_%28mechanics%29http://en.wikipedia.org/wiki/Journal_%28mechanics%29http://en.wikipedia.org/wiki/Journal_%28mechanics%29http://en.wikipedia.org/wiki/Gimbalhttp://en.wikipedia.org/wiki/Gimbalhttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Axlehttp://en.wikipedia.org/wiki/Axlehttp://en.wikipedia.org/wiki/Axlehttp://en.wikipedia.org/wiki/Gimbalhttp://en.wikipedia.org/wiki/Gimbalhttp://en.wikipedia.org/wiki/Gimbalhttp://en.wikipedia.org/wiki/Flight_dynamicshttp://en.wikipedia.org/wiki/Flight_dynamicshttp://en.wikipedia.org/wiki/Flight_dynamicshttp://en.wikipedia.org/wiki/Flight_dynamicshttp://en.wikipedia.org/wiki/Flight_dynamicshttp://en.wikipedia.org/wiki/Flight_dynamicshttp://en.wikipedia.org/wiki/Flight_dynamicshttp://en.wikipedia.org/wiki/Image:Gyroscope_wheel_animation.gifhttp://en.wikipedia.org/wiki/Flight_dynamicshttp://en.wikipedia.org/wiki/Flight_dynamicshttp://en.wikipedia.org/wiki/Flight_dynamicshttp://en.wikipedia.org/wiki/Gimbalhttp://en.wikipedia.org/wiki/Axlehttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Gimbalhttp://en.wikipedia.org/wiki/Journal_%28mechanics%29http://en.wikipedia.org/wiki/Coordinate_axishttp://en.wiktionary.org/wiki/rotor
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    gimbals. A control moment gyroscope (CMG) is an example of a fixed-output-gimbal device

    that is used on spacecraft to hold or maintain a desired attitude angle or pointing direction

    using the gyroscopic resistance force.

    In some special cases, the outer gimbal (or its equivalent) may be omitted so that the rotor has

    only two degrees of freedom. In other cases, the center of gravity of the rotor may be offset

    from the axis of oscillation, and thus the center of gravity of the rotor and the center of

    suspension of the rotor may not coincide.

    Properties

    A gyroscope in operation with freedom in all three axes.

    The rotor will maintain its spin axis direction regardless of the orientation of the outer

    frame.

    A gyroscope exhibits a number of behaviours includingprecessionandnutation. Gyroscopes

    can be used to construct gyrocompasseswhich complement or replace magnetic compasses

    (in ships,aircraft and spacecraft,vehicles in general), to assist in stability (bicycle,Hubble

    Space Telescope,ships,vehiclesin general) or be used as part of anInertial guidance system.

    Gyroscopic effects are used in toys likeyo-yosandPowerballs. Many other rotating devices,

    such asflywheels, behave gyroscopically although the gyroscopic effect is not used.

    The fundamental equation describing the behavior of the gyroscope is:

    where the vectors and are, respectively, the torque on the gyroscope and its angular

    momentum, the scalar is its moment of inertia, the vector is its angular velocity, and the

    vector is its angular acceleration.

    http://en.wikipedia.org/wiki/Precessionhttp://en.wikipedia.org/wiki/Precessionhttp://en.wikipedia.org/wiki/Precessionhttp://en.wikipedia.org/wiki/Nutationhttp://en.wikipedia.org/wiki/Nutationhttp://en.wikipedia.org/wiki/Nutationhttp://en.wikipedia.org/wiki/Gyrocompasshttp://en.wikipedia.org/wiki/Gyrocompasshttp://en.wikipedia.org/wiki/Shiphttp://en.wikipedia.org/wiki/Shiphttp://en.wikipedia.org/wiki/Aircrafthttp://en.wikipedia.org/wiki/Aircrafthttp://en.wikipedia.org/wiki/Spacecrafthttp://en.wikipedia.org/wiki/Spacecrafthttp://en.wikipedia.org/wiki/Spacecrafthttp://en.wikipedia.org/wiki/Vehiclehttp://en.wikipedia.org/wiki/Vehiclehttp://en.wikipedia.org/wiki/Vehiclehttp://en.wikipedia.org/wiki/Bicyclehttp://en.wikipedia.org/wiki/Bicyclehttp://en.wikipedia.org/wiki/Bicyclehttp://en.wikipedia.org/wiki/Hubble_Space_Telescopehttp://en.wikipedia.org/wiki/Hubble_Space_Telescopehttp://en.wikipedia.org/wiki/Hubble_Space_Telescopehttp://en.wikipedia.org/wiki/Hubble_Space_Telescopehttp://en.wikipedia.org/wiki/Shiphttp://en.wikipedia.org/wiki/Shiphttp://en.wikipedia.org/wiki/Shiphttp://en.wikipedia.org/wiki/Vehiclehttp://en.wikipedia.org/wiki/Vehiclehttp://en.wikipedia.org/wiki/Vehiclehttp://en.wikipedia.org/wiki/Inertial_guidance_systemhttp://en.wikipedia.org/wiki/Inertial_guidance_systemhttp://en.wikipedia.org/wiki/Inertial_guidance_systemhttp://en.wikipedia.org/wiki/Yo-yohttp://en.wikipedia.org/wiki/Yo-yohttp://en.wikipedia.org/wiki/Yo-yohttp://en.wikipedia.org/wiki/Powerball_%28toy%29http://en.wikipedia.org/wiki/Powerball_%28toy%29http://en.wikipedia.org/wiki/Powerball_%28toy%29http://en.wikipedia.org/wiki/Flywheelhttp://en.wikipedia.org/wiki/Flywheelhttp://en.wikipedia.org/wiki/Flywheelhttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Angular_momentumhttp://en.wikipedia.org/wiki/Angular_momentumhttp://en.wikipedia.org/wiki/Angular_momentumhttp://en.wikipedia.org/wiki/Image:Gyroscope_operation.gifhttp://en.wikipedia.org/wiki/Image:Gyroscope_operation.gifhttp://en.wikipedia.org/wiki/Image:Gyroscope_operation.gifhttp://en.wikipedia.org/wiki/Image:Gyroscope_operation.gifhttp://en.wikipedia.org/wiki/Image:Gyroscope_operation.gifhttp://en.wikipedia.org/wiki/Image:Gyroscope_operation.gifhttp://en.wikipedia.org/wiki/Image:Gyroscope_operation.gifhttp://en.wikipedia.org/wiki/Angular_momentumhttp://en.wikipedia.org/wiki/Angular_momentumhttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Flywheelhttp://en.wikipedia.org/wiki/Powerball_%28toy%29http://en.wikipedia.org/wiki/Yo-yohttp://en.wikipedia.org/wiki/Inertial_guidance_systemhttp://en.wikipedia.org/wiki/Vehiclehttp://en.wikipedia.org/wiki/Shiphttp://en.wikipedia.org/wiki/Hubble_Space_Telescopehttp://en.wikipedia.org/wiki/Hubble_Space_Telescopehttp://en.wikipedia.org/wiki/Bicyclehttp://en.wikipedia.org/wiki/Vehiclehttp://en.wikipedia.org/wiki/Spacecrafthttp://en.wikipedia.org/wiki/Aircrafthttp://en.wikipedia.org/wiki/Shiphttp://en.wikipedia.org/wiki/Gyrocompasshttp://en.wikipedia.org/wiki/Nutationhttp://en.wikipedia.org/wiki/Precession
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    It follows from this that a torque applied perpendicular to the axis of rotation, and therefore

    perpendicular to , results in a motion perpendicular to both and . This motion is called

    precession. The angular velocity of precession is given by thecross product:

    Precession on a gyroscope

    Precession can be demonstrated by placing a spinning gyroscope with its axis horizontal and

    supported loosely (frictionless toward precession) at one end. Instead of falling, as might be

    expected, the gyroscope appears to defy gravity by remaining with its axis horizontal, when

    the other end of the axis is left unsupported and the free end of the axis slowly describes a

    circle in a horizontal plane, the resulting precession turning. This effect is explained by the

    above equations. The torque on the gyroscope is supplied by a couple of forces: gravity

    acting downwards on the device's centre of mass, and an equal force acting upwards to

    support one end of the device. The motion resulting from this torque is not downwards, as

    might be intuitively expected, causing the device to fall, but perpendicular to both the

    gravitational torque (downwards) and the axis of rotation (outwards from the point of

    support), i.e. in a forward horizontal direction, causing the device to rotate slowly about the

    supporting point.

    As the second equation shows, under a constant torque due to gravity or not, the gyroscope'sspeed of precession is inversely proportional to its angular momentum. This means that, for

    instance, if friction causes the gyroscope's spin to slow down, the rate of precession increases.

    This continues until the device is unable to rotate fast enough to support its own weight,

    when it stops precessing and falls off its support, mostly because friction against precession

    cause another precession that goes to cause the fall.

    By convention, these three vectors, torque, spin, and precession, are all oriented with respect

    to each other according to theright-hand rule.

    To easily ascertain the direction of gyro effect, simply remember that a rolling wheel tends,when entering a corner, to turn over to the inside.

    http://en.wikipedia.org/wiki/Precessionhttp://en.wikipedia.org/wiki/Precessionhttp://en.wikipedia.org/wiki/Cross_producthttp://en.wikipedia.org/wiki/Cross_producthttp://en.wikipedia.org/wiki/Cross_producthttp://en.wikipedia.org/wiki/Right-hand_rulehttp://en.wikipedia.org/wiki/Right-hand_rulehttp://en.wikipedia.org/wiki/Right-hand_rulehttp://en.wikipedia.org/wiki/Image:Gyroscope_precession.gifhttp://en.wikipedia.org/wiki/Image:Gyroscope_precession.gifhttp://en.wikipedia.org/wiki/Image:Gyroscope_precession.gifhttp://en.wikipedia.org/wiki/Image:Gyroscope_precession.gifhttp://en.wikipedia.org/wiki/Image:Gyroscope_precession.gifhttp://en.wikipedia.org/wiki/Image:Gyroscope_precession.gifhttp://en.wikipedia.org/wiki/Image:Gyroscope_precession.gifhttp://en.wikipedia.org/wiki/Right-hand_rulehttp://en.wikipedia.org/wiki/Cross_producthttp://en.wikipedia.org/wiki/Precession
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    EXERCISE QUESTIONS:

    1) WHAT IS GYROSCOPE?

    2) DRAW A NEAT SKETCH OF GYROSCOPE.


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