Classification of Electrical Transducers

 Transducers may be classified according to their structure, method of energy conversion and application. Thus we can say that transducers are classified

 •           As active and passive transducer

•           According to transduction principle

•           As analog and digital transducer

•           As primary and secondary transducer

•           As transducer and inverse transducer

 Active and Passive Transducer

 Active Transducers

·         Active transducers are self-generating type of transducers.

·         These transducers develop an electrical parameter (i.e. voltage or current) which is proportional to the quantity under measurement.

·         These transducers do not require any external source or power for their operation.

·         They can be subdivided into the following commonly used types

Passive Transducers

·         Passive transducers do not generate any electrical signal by themselves.

·         To obtain an electrical signal from such transducers, an external source of power is essential.

·         Passive transducers depend upon the change in an electrical parameter (R, L, or C).

·         They are also known as externally power driven transducers.

·         They can be subdivided into the following commonly used types.

According to Transduction Principle

The transducers can be classified according to principle used in transduction.

 •           Capacitive transduction

•           Electromagnetic transduction

•           Inductive transduction

•           Piezoelectric transduction

•           Photovoltaic transduction

•           Photoconductive transduction

 Analog and Digital Transducers

 The transducers can be classified on the basis of the output which may be a continuous function of time or the output may be in discrete steps.

 Analog Transducers

·         These transducers convert the input quantity into an analog output which is a continuous function of time.

·         A strain gauge, LVDT, thermocouples or thermistors are called analog transducers as they produce an outp which is a continuous function of time.

 Digital Transducers

·         Digital transducers produce an electrical output in the form of pulses which forms an unique code.

·         Unique code is generated for each discrete value sensed.

 Primary or Secondary

·         Some transducers consist of 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 Bourdons 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.

 Transducer and Inverse Transducer

·         Transducers convert 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.