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Transducers, Eee, , 7.1 Introduction, , A “wansducer" is a device which converts one form of energy into another form, In many applications a, non-electrical parameter like heat, intensity of light, liquid level, humidity etc. is converted into electrical lorm by, means of transducers, Itis a device which converts 4 physical quantity or a physical condition into an electrical, signal. Transducers are also known as "Pick up”. A transducer may be imagined to consist of two important and, closely related parts which are -a sensing element and a transduction element, , Advantages of Electrical Transducers, , A transducer converts a physical quantity into an analogous electrical quantity with the following, advantages:, , () The effect caused due frictional forces are minimized,, , (ii) The power handied by the electrical and electronic devices are reduced,, (aii) Amplification and attenuation of electrical quantities becomes easier, () The electrical output can be easily transmitted and processed,, , Classifications of Transducers, Transducers are classilied in various ways as shown below,, , ey, , , , , , eon als: Panebenle Wantieae’ Tiss ieatehtoid Tete, Primary and Secondary Transducers, * Primary: A transducer which is directly connected to the measurable quantily is known as a primary, transducer., * Secondary: A transducer which is not directly connected to the measurable Quantity of input is, known as @ secondary transducer., , Scanned with CamScanner

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eee, , Example; An example of primary ay, , . id sec lon, jubo diets AS a primary transducer as k oo Transducer is shown in Figure 7 1. Here, —, =e me, , The dispkACeMent outpUT of the Bo S808 the prossure of force and converts into a displac', , ouput vollage proportional to q ae lube moves the core of LVDT and converts it into an electrical, : ISplacy, , secondary transducer. Ment in turn proportional to pressure here, LVDT acts as a, , Froe ond, , , , 0 -Slie=, , , , 12 Active and Passive Transducers, , itive Transducer, Active transducers are those transducers, which uses their own developed voltage or current for giving, , , , supul signal. The energy required for producing this output signal is obtained from the physica! quantity, sg measured and doesn't require an external power supply., , Example: Thermocouple, photovoltaic cell, tachogenerator, piezoelectric transducers, accelerometer etc., “3v27 2 shows an active transducer,, , fasive Transducer, , Passive transducers are those transducers which uses an external power supply for converting the non‘ical Quantity to an electrical quantity., Example: Resistive, inductive and capacitive transducers (A, L, C transducers), potentiometer, LVDT, , , , , , is ducers". Whereas passive transducers ‘, , , , 13 Analog Transducers, , ‘log Transducers, Analog transducers convert the input quantity into an analog output which is a continues in time., Example: Strain gauge. LVDT, a thermocouple or a thermistor., , Scanned with CamScanner

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Digital Transducers, , IT the pat quantity (6 Converted inte an electrical output which 1s in chgital form (or pulses) then, the typ,, Of transducer is cated a dagtal transducer, , Example: Moto electie transducer, , , , , , Direction of acceteration, , , , , , , , , , , , , , , , , , 7.4 Measurement of Displacement using Transducers, , « Someoct the transducers can convert the input displacement into a corresponding output electrical, vollage end hence, can be used for the measurement of displacement. The transducers used for ths, , purpose are, 1. Potertiometer, 2. Linear variable diferential transformer (LVDT), 3. Hall vansoucer, * Theses transducers have been described in detail one by one as follows., , 1. Potentiometer, * Aresistance potentometer is also called simply a “POT”. It consists of a resistive element provided, with a sliding contact, which is called “vaper”, It 6 & "passive ansducer” since it reques an external power source for it's operation,, The resistive body of the potentiometer may be wire wound where a 0.01 mm diameter of platinum, nickle alloy «s wound on an insulated metal., ° Figure 7 4 shows a loaded potentiometer used for the measurement of displacement., , Se —_——_—— — —— TA, , , , Scanned with CamScanner

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ets, , Where., , , , Quiput ewes meter, Figure-7 4: A potentiometer for measurement of displacement, , Here, outpul voltage, «, = Xa Of, ¢, a x, a displacement, , @,and e@, = input and output voltages (in V), x, = total length of pot (in m), x, = displacement of wiper from zero position (in m), A, = total resistance of potentiometer, , Therefore, the output voltage of a potentiometer linearly varies with the displacement., , , , A A transducer converts, , (a) mechanical energy into electrical energy., , (b) mechanical displacement into electrical signal., (c) one form of energy into another form of energy., (d) electrical energy into mechanical form., , Solution: (c), , * The sensitivity of a potentiometer is given by, , __ouiput voltage _ m4, pia * S= % x, The sensitivity of a potentiometer should be high souks the input voltage should, be large and resistance A, should be high, But, for linearity of the potentiometer, the, resistance of potentiometer, A, should be an low as possible. Therefore, a compromise, between the linearity and sensitivity is made in a potentiometer., * The loading effect on the potentiameter (i.e. power dissipation) is minimized by using, @ voltmeter of higher voltmeter sensitivity which is connected at the output terminal, of the potentiometer., , of a Resistance Potentiometer, , A resistance potentiometer has following advantages:, , (i) They are less costly, , (ii) Ther operation is simple, , (ui) Useful for measurement of large amplitude of displacement, (iv) Their electrical efficiency is high., , es of a resistance Potentiometer, (i) Mtrequire a large force for wiper movement, (i) The ie of the transducer is limited due to wear and tear problem of the wiper., , , , , , , , Scanned with CamScanner

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voltage for a displacement of 2 mm., , , , An inverse transducer converts, (a) electrical energy to any ather form of energy, (b) electrical energy to light energy, (c) mechanical displacement into electrical signal, (d) electrical energy to mechanical form, Solution: (a) :, An inverse transducer is one which converts an electrical input into a non-electrical output,, , Ea Which of the following acts as an active transducer?, , , , , , , , (a) Photo emissive cell (b) Selsyn, (c) Strain gauge (d) Photo voltaic cell, Solution: (d), , Which one of the following can act as an inverse transducer?, (a) electrical resistance potentiometer (b) LVDT, (c) Capacitive transducer (d) piezo-electric crystals, Solution: (d), , An “inverse transducer” is defined as a device which converts an electrical quantity into a non-slectricay, Quantity. Pi¢z0-elactrical crystal is an example of such transducer., , , , A resistance potentiometer has a sensitivity of 10 vimm. Find the output |, , , , Solution:, We know that, g= Quiputvoltage _V, _Y, , Displacement x x, or, Vi = Sx,, Given x, = 2mm and S= 10 Vimm, So, output voltage, V, = 10 x 2 = 20 volts, A resistance potentiometer is a, (a) first order instrument ({b) zero order instrument, (c) second order instrument (d) none of the above, Solution: (6), The output vollage in a potentiometer for an input displacement of x,is given by, , Vv, = 4%, om Sexy,, , or, Va kx, (k= constant = “.), , %, , -. Transter function, No(s) ak, X,(8), , Therefore, a resistance potentiometer is a zero-order instrument., , ——_—_——— SSS, , , , Scanned with CamScanner