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INDUCTIVE TYPETRANDUCERS

BY -ARPITA NAYYAR (02)CHANCHAL THAWANI (04)DEEPA KHIYANI (18)MITALI VYAS (20)

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nA Transduceris a device that converts oneform of energy to another.

n Energy type can be any includingelectrical, mechanical, chemical etc.

n Transducers are widely used in measuring

instruments.n Transducers commonly implies the use of

a sensor or detector.

INTODUCTION

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Principle of inductive typetransducers It works on the principle of the magnetic

induction of magnetic material. It operates on the principle that the

relative motion between a conductor and amagnetic field induces a voltage in theconductor.

Because the pressure induced electricaloutput signal requires relative motion, theinductive design is limited to dynamicmeasurements.

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n In practice, this means that an

electric current will be induced inany closed circuit when themagnetic flux through a surface

bounded by the conductor changes.This applies whether the field itselfchanges in strength or the conductoris moved through it.

n The induced electromotive force(EMF) in any closed circuit is equalto the time rate of change of themagnetic flux through the circuit.

http://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Electrical_networkhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Electrical_networkhttp://en.wikipedia.org/wiki/Electric_current

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Classification of tranducers

n There are two common type ofinductive tranducers :

n Simple inductance type

nAnd two coil inductance type.

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CONSTRUCTIONn Simple inductance type tranducers

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n

Two coil mutual inductance type

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Factors affecting the inductance

type transducern `NUM BE R OF W I R E W R AP S , OR " T UR NS " I N T H E C O I L :

n C O I L A R E A :

n C O I L L E N G T H :

n C ORE M ATE R IAL :

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n An ac source is given to the primary. This ac source excites theprimary and a flux is produced.

n This flux is linked to the secondary coil and thus a voltage V isinduced. If the mutual inductance between the primary andsecondary windings is represented by M (Hertz) and the frequency

of ac excitation is represented by w, then the voltage V developedin secondary coil can be written as

n V = MwIp.Ip - The current due to excitation in primary (Amperes).

n The current in the primary coil produces a magnetic flux that links

with the secondary coil through the displacement plate. Thus, themovement of the ferromagnetic plate to the right causes a greatervalue of flux linkage between the two terminals. This in turn causesan increase in the resulting output voltage across the secondaryterminal with a value of (T1-T2). This output is given to the input of

the CRO or a recorder and the amount of displacement can beknown in terms of volta e.

working

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I N T R O D U C T I O Nn LVDTnThe Linear Variable Differential

Transducer (LVDT) is the mostbroadly used variable-inductancetransducer in industry. It is anelectro-mechanical device designed

to produce an AC voltage outputproportional to the relativedisplacement of the transformer andthe armature.

n Typical LVDT

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n Input: Power input is a 3 to 15 V (rms) sine wave with afrequency between 60 to 20,000 Hz (the two mostcommon signals are 3 V, 2.5 kHz and 6.3 V, 60 Hz).

n Stroke: Full-range stroke ranges from 125 m to75 mm (0.005 to 3 in).

n Sensitivity: Sensitivity usually ranges from 0.6 to 30 mVper 25 m (0.001 in) under normal excitation of 3 to 6 V.Generally, the higher the frequency the higher thesensitivity.

n Nonlinearity: Inherent nonlinearity of standard units is onthe order of 0.5% of full scale.

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PR INC IPLE n LVDT:n LVDT works under the principle of

mutual induction, and thedisplacement which is a non-electricalenergy is converted into an electrical

energy. And the way how the energyis getting converted is described inworking of LVDT in a detailedmanner.

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C O N S T R U C T I O NLVDT consists of a cylindrical formerwhere it is surrounded by one primarywinding in the centre of the formerand the two secondary windings at

the sides. The number of turns in boththe secondary windings are equal, butthey are opposite to each other, i.e., ifthe left secondary windings is in theclockwise direction, the right

secondary windings will be in the anti-clockwise direction, hence the netoutput voltages will be the differencein voltages between the twosecondary coil. The two secondary coil

is represented as S1 and S2 Esteemiron core is placed in the centre of thecylindrical former which can move into and fro motion as shown in thefigure. The AC excitation voltage is 5to 12V and the operating frequency is

given by 50 to 400HZ.

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lThe device consists of an armthat moves linearly accordingto the displacementproduced. It also consists of asingle coil wound on a former

with N number of turns. Theend of the arm is connectedto a soft iron core whichmoves linearly along the axisof the former. Thus,

reluctance R will beproduced due to the fluxpath. The coil inductance ofthe device can be written bythe equation, L= N2 /R.

WORKING OFLVDT

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n A linear movement of the arm to the right decreasesthe reluctance R of the flux path. Thus, accordingto the equation given above, the inductance

increases due to the decrease in reluctance and viceversa. This inductance L can be calculated orrecorded with the help of an inductance bridge orthrough a recorder. Thus the measure of the

displacement of the arm can be obtained from thecorresponding change in inductance.If the transducer is connected to the input of anoscillator tank circuit, the change in frequency f of

the oscillator could be taken as the measurement forthe corresponding change in the displacement of thearm. A displacement of the arm changes theinductance and hence the frequency. Thus, the

output can be measured in terms of inductance andfre uenc

http://www.instrumentationtoday.com/?p=15http://www.instrumentationtoday.com/?p=15

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LET US STUDY BYCASES Let's study the working of LVDT by splitting the

cases into 3 based on the iron core positioninside the insulated former.Case 1:On applying an external force which is thedisplacement, if the core remains in the nullposition itself without providing any movement

then the voltage induced in both the secondarywindings are equal which results in net output isequal to zero

i.e., Esec1-Esec2=0

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n Case 2:

When an external force is appilied and ifthe steel iron core tends to move in theleft hand side direction then the emfvoltage induced in the secondary coil 1is greater when compared to the emfinduced in the secondary coil 2.

Therefore the net output will be Esec1-Esec2

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n Case 3:

When an external force is applied and ifthe steel iron core moves in the right

hand side direction then the emfinduced in the secondary coil 2 isgreater when compared to the emfvoltage induced in the secondary coil 1.

therefore the net output voltage will ben Esec2-Esec1

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A D V A N TA G E S O F LV D T Infinite resolution is present in LVDT High output

LVDT gives High sensitivity Very good linearity Ruggedness LVDT Provides Less friction Low hysteresis LVDT gives Low power consumption.

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D I S A D V A N TA G E S O F LV D TnVery high displacement is required for

generating high voltages.n Shielding is required since it is sensitive

to magnetic field.n The performance of the transducer gets

affected by vibrationsn Its is greatly affected by temperature

changes.

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A P P L I C AT I O N O F LV D Tn LVDT is used to measure displacement

ranging from fraction millimeter to

centimeter.

nActing as a secondary transducer, LVDTcan be used as a device to measureforce, weight and pressure, etc..

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TH AN K YOU ! !!