Transducers are devices which convert one form of energy into another form of energy. Different types of transducers are classified as follows:

1. Active & passive transducers
2. Analog & digital transducers
3. Primary or secondary transducers

4. Transducers and inverse transducers

    

5. Active and Passive Transducers:

• Active Transducers:

Devices which do not require power for transduction from the external source and draw power from the input applied are called as active transducers. Active transducers are self-generating devices, which operate under the energy conversion principle and generate an equivalent output signal (for example from pressure to charge or temperature to electrical potential). Thermocouple and photovoltaic cells are examples of active transducers.

• Passive Transducers:

Devices which require power for transduction from the external source i.e. auxiliary power are known as passive transducers. Passive transducers operate under energy controlling principles, which make it necessary to use an external electrical source with them. They depend upon the change in electrical parameters (R, L and C). Typical examples of passive transducers are Differential transformers, Resistance strain gauge and capacitive transducers.

1. Analog and Digital

• Analog Transducers:

Devices which convert the input quantity into analog output are known as Analog Transducers. Analog output is a continuous function of time. Strain gauge and LVDT are the examples of Analog transducers.

• Digital Transducers:

Devices which convert the input quantity into Digital output are known as Digital Transducers, Digital Output is in the form of non continuous pulses. Laser beam instruments and vortex flow meters are the common examples of Digital Transducers.

1. Primary or Secondary

• Some transducers consist of a mechanical device along with the electrical device. In such transducers mechanical device acts as a primary transducer and converts physical quantity into mechanical signal.
• The electrical device then converts mechanical signal produced by primary transducer into an electrical signal. Therefore, electrical device acts as a secondary transducer.

• For an example, in pressure measurement Bourdon's tube acts as a primary transducer which converts a pressure into displacement and LVDT acts as a secondary transducer which converts this displacement into an equivalent electrical signal.

   

1. Transducer and inverse transducer

• Transducer converts non-electrical quantity into electrical quantity whereas inverse transducer converts electrical quantity into non-electrical quantity.
• For example, microphone is a transducer which converts sound signal into an electrical signal whereas loudspeaker is an inverse transducer which converts electrical signal into sound signal.