Transducer Classification

The device which converts energy from one form to another form is known as a transducer. The input energy may be Electrical, mechanical, Thermal, Chemical, or Optical. These are used to measure non-electrical quantities. For example Pressure, Force, Velocity, Ph Value, Temperature, Light intensity. 

It is a device that is connected to the sensor. It is to convert the measured quantity into a standard electrical signal. Such as 0-10V DC, -10 to +10V DC, etc. The output of transducer can be directly used by system designer. It is somewhat different to sensors.


Elements of Transducer
Elements of Transducer

It may be thought of consisting of two and closely related elements.

  1. Sensing or Detecting Element: This element senses/detects the physical quantity.
  2. Transduction Element: This element transfers the output of the sensing element into an electrical output.

In addition, a transducer may have amplifiers, power supply and calibrated scale.


Electrical Transducers: Transducers which give electrical energy as output. For example voltage, current, power and frequency.

Displacement Transducers: They convert the displacement of mechanical energy into electrical energy.

Optoelectronic Transducers: They convert light energy into electrical energy. For example solar cells, a photoconductive cell, photovoltaic cell, Light Dependent Resistor etc.

Electrical transducers are the most popular. A non-electrical quantity like force or pressure is measured with these. By changing them into electrical quantities.


  • Mechanical Ruggedness: It should be mechanically strong. It should be able to withstand the working conditions and mechanical strains.
  • Linear Output Input Characteristic: It should have a linear output/input characteristic.
  • Reliability: The results should be reliable. The result should not change with temperature and other changes and should also be stable.
  • Good Response: If the input to the transducer varies with time the transducer should have a good response to the variations.
  • Low Noise: The noise/signal ratio should be low so that its output can be directly measured with sufficient accuracy.


  1. Amplification or attenuation of an electrical quantity becomes easier with these devices.
  2. Electrical Transducers minimizes the effect of friction.
  3. Controlling of Electrical and Electronics system are easier with these transducers.
  4. The use of Integrated Circuits (IC’s) has brought a revolution in the field of instrumentation.
  5. Process, reception and transmission of electrical output becomes easier with transducers


(1) Primary and Secondary Transducers

  • Primary transducers: They convert the physical quantity under measurement directly into electrical output after sensing (detecting) the quantity, e.g. thermocouples.
  • Secondary transducers: The sensed physical quantity firstly converted into analog output and converted into an electrical output

Example : LVDT used with a Boueden tube to measure pressure.

(2) Analog and Digital Transducers:

  • Analog transducers: They give electrical output in analog form, e.g., strain gauges, LVDT, Thermocouple, etc.
  • Digital transducers: They give electrical output in digital form.

 (3) Active and Passive Transducers:

  •  Active transducers: They develop their own voltage or current as the output. They obtain energy from the physical quantitiy being measured.

Example are thermocouple piezoelectric transducer photovoltaic cell, photoelectrical cell, etc.

  • Passive transducers: they do not have to develop voltage or current of their own and need an external power source for the purpose.

Example strain gauge, Thermistor, LVDT, Hall effect generator etc.


(1) Electrical/Electronics

  • A microphone is a transducer which converts the sound signal into electrical energy. A loudspeaker is a transducer which converts electrical signal back to sound energy.
  • The video camera is a transducer which converts a picture into electrical energy. The picture tube is a transducer which converts back the electrical energy into light (picture). TV transmission and reception uses this principle.
Mike, Loud Speaker and Camera are also Transducers.

(2) The human system also has many transducers:

  • The human ear acts as a transducer. It converts sound into electrical pulses which go to our brain. The train also as a transducer and reconverts back the electrical signal into the original sound and hence we feel the sound.
  • The human eve acts as a transducer which converts a picture into electrical pulses which go to our brain which, in turn also acts as a transducer and reconverts back the electrical pluses into the original picture and thus we can see the object.

Our eye is like a camera which can take infinite photographs black and white as well as color simultaneously and can send them to the brain.

Read Also:  Introduction to Measuring Instruments