Chapter: Measurements and Instrumentation - Transducers and Data Acquisition Systems

Classification of Electrical Transducers

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

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

 

Ø     Active transducers are self-generating type of transducers.

 

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

 

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

 

 

Ø   They can be subdivided into the following commonly used types

 


 

Passive Transducers

 

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

 

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

 

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

 

Ø     They are also known as externally power driven transducers.

 

 

Ø     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

 

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

 

Ø 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

 

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

 

Ø   Unique code is generated for each discrete value sensed.

 

Primary or Secondary

 

Ø     Some transducers consist of mechanical device along with the electrical device.

 

Ø     In such transducers mechanical device acts as a primary transducer and converts physical quantity into mechanical signal.

 

Ø     The electrical device then converts mechanical signal produced by primary transducer into an electrical signal.

 

Ø     Therefore, electrical device acts as a secondary transducer.

 

Ø     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

 

Ø     Transducers convert non-electrical quantity into electrical quantity whereas inverse transducer converts electrical quantity into non-electrical quantity.

 

Ø     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.

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