- Practice · 5 marks
Classification of transducers with examples
Short answer
Transducers are classified by energy source (active/passive), function (primary/secondary), output (analog/digital), principle, etc. Active transducers generate output directly from the measurand (e.g., thermocouple); passive need external excitation and change R, L or C (e.g., strain gauge). Primary converts measurand into mechanical signal (e.g., Bourdon tube); secondary converts that into electrical (e.g., LVDT).
Classify transducers. Differentiate between active and passive transducers, and between primary and secondary transducers, with examples.
A transducer converts one form of energy or physical quantity into another, usually into an electrical signal. A sensor is the sensing element of a transducer.
Classification
- By energy source: active (self-generating) and passive.
- By function: primary (sensing) and secondary.
- By output signal: analog and digital.
- By principle: resistive, capacitive, inductive, piezoelectric, thermoelectric, photoelectric, Hall effect.
- By quantity measured: displacement, force, pressure, temperature, flow and so on.
- By operating mode: transducers (input-to-output converters) and inverse transducers.
Active and passive
| Point | Active transducer | Passive transducer |
|---|---|---|
| Power | Generates output emf or charge from the measurand | Needs external excitation |
| Also called | Self-generating | Externally powered |
| Output | Voltage, charge, current | Change in R, L or C |
| Examples | Thermocouple, piezoelectric crystal, photovoltaic cell | Strain gauge, thermistor, LVDT, potentiometer |
Primary and secondary
- Primary transducer: first element in contact with the measured quantity; it converts it into a mechanical or other signal. Example: a bourdon tube turns pressure into displacement.
- Secondary transducer: converts the output of the primary into an electrical signal. Example: a potentiometer or LVDT attached to the bourdon tube gives voltage.
A load cell is a combination: an elastic member (primary) with strain gauges (secondary).
✓ Answer checked by Claude Opus 5.5 (high effort)
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