Transducer and its classification

A transducer is a device that can convert a physical quantity into another.

Most transducers convert nonelectric quantities into electrical quantities. So transducers act as energy converters.

A transducer can be divided into a primary sensing element and a converter element. A primary sensing element detects a quantity to be measured and a converter element transforms input power into another mostly an electrical signal.

Classification of transducers:

Basically, there are two types of transducers 1. Mechanical 2. Electrical.

Mechanical transducer:

Mechanical transducers are those primary sensing elements, that respond to the changes in the physical state of a system and give output in a different form.

Mechanical transducers are distinguished from electrical transducers as their output signals are mechanical. Most of the mechanical transducers are used as primary transducers. 

  • An example is a Bimetallic strip. It is a mechanical transducer, when it is subjected to heat or temperature it responds with a mechanical displacement.
  • Fluid expansion or air pressure entry in a bourdon tube of a pressure gauge makes the rotary motion of the indicating pointer.
  • Bellows, the diaphragm is commonly used for pressure measurement expands results in a displacement.  

Electrical transducers: In general electrical transducers are classified according to their method of energy conversion, signal nature. Resistance thermometer(RTD) when exposed to heat, the resistance of the element changes. Hence it is an electrical transducer. 

Electrical transducers:

They are classified

1.Active and passive

2.Based on transduction

3.Analog and digital

4.Transducer and inverse transducer

5. Primary and Secondary

Active Transducer:

This transducer is also known as a self-generating energy transducer. Examples of this kind of transducers are thermocouples, piezoelectric transducers, Photoelectric cells, moving coil generator.

Passive Transducer:

Passive transducer does not generate any electrical output themselves, an external source of power is essential to get the electrical output signal. They are also known as externally power-driven transducers.

Passive transducers are subdivided into inductive, capacitive, and resistive transducers.

An example of an inductive transducer is LVDT.

An example of a resistive transducer is a strain gauge.

An example of a capacitive transducer is thermoemissive.

Transducer based on transduction:

Depending upon how they convert input electrical quantity into resistance, capacitance, and inductance is called transduction.

They can be classified as Thermoelectric, Magnetostrictive, Optical transducers.

Analog and Digital:

Analog transducer converts the input physical quantity into analog output quantity which is a continuous function of time.

Example: LVDT, Strain gauge, Thermocouple, Thermistors.

Digital Transducer converts the input physical quantity into digital form. pulses in the form of logic 0 and 1.

Example: Rotary encoder.

Transducer and inverse transducer:

Transducers convert the nonelectrical quantity into an electrical signal whereas an inverse transducer converts an electrical signal into a nonelectrical signal.

For example, a microphone is a type of transducer that converts the sound signal into an electrical signal whereas a loudspeaker is an inverse transducer that converts an electrical signal into a sound signal in a nonelectrical quantity.

Primary or Secondary Transducer:

Some transducers consist of the mechanical device also with the electrical device. In such a type of transducers, a mechanical device acts as a primary transducer and changes the physical quantity into a mechanical deformation signal.

The electrical device then transforms the mechanical signal produced by the primary transducer into an electrical signal. Therefore the electrical device acts as a secondary transducer.

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

Author: PSS Bapu Rao

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