Before going to the classifications we have to check-out, what are transducers? In electrical instrumentation, transducer is a device which coverts physical quantity into an electrical quantity. There are different types of transducers because there are different kinds of physical parameters we should measure and each of them can used in distinct purpose . So let’s check on classification of transducers.
NB: Transducer is also known as “Pick-up”.
Classifications:-
1.Based upon transduction principle used 2. Primary & Secondary transducers 3.Active & Passive transducers 4. Analoge & Digital transducers 5.Transducers & Inverse transducers
1.Based upon the transduction principle:-
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Resistance - Potentimeter devices, Resistance strain gauge, Pirani guage or hot wire meter, Resistance thermometer, Thermister, Resistance hygrometer, Photoconductive cell.
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Capacitance - Variable capacitance pressure gauge, Capacitor microphone, Dielectric gauge.
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Inductance - Magnetic circuit transducer, Reluctance pick-up, Differential transformer, Eddy current guage, Magneto striction gauge.
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Voltage & Current - Hall effect transducer, Ionisation chamber, Photoemissive cell, Photomultiplier tube.
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Self generating transducers - Thermocouple, Thermopile, Moving coil generator, Piezoelectric transducer, Photovoltaic.
2. Primary & Secondary transducers:-
Look at the above picture, it is easy to understand the concept with this picture. Here the measuring variable pressure is passed through bourdon tube. Bourdon converts the pressure into displacement by the movement of free end. This displacement is transferred to iron core of LVDT. LVDT converts displacement to voltage. Here bourdon tube acts as primary transducer and LVDT acts as secondary transducer.
3. Active & Passive:-
Transducers those which don’t require an auxilary power source to produce their output are known as ‘Active transducers’ or self generating type. eg: Moving coil, Piezoelectric crystal, Thermocouple, Photovoltaic cell. On the other hand transducer that can’t work on the absence of external power supply are called ‘passive transducers’. eg: Resistive, Capacitive, Inductive.
4. Analoge & Digital :-
Analoge transducers converts input quantity into an analog output which is continous function of time. eg: strain gauge, LVDT, Thermocouple. Thermister.
Digital transducer converts input quantity into an electrical output is in the form of pulses eg: Glass scale, Metallic scale.
5. Transducers & Inverse Transducers
We have already looked into transducers, inverse transducers are just the opposite of transducers in function. I Inverse transducers converts electrical quantity in non electrical quantity. Just think about an current coil moving in magnetic field which is an inverse transducer. eg: Peizoelectrical crystal.