What is transducer?

The non-electrical quantity is converted into an electrical form for using electrical methods and techniques for measurement, manipulation and control. The device which when actuated, transforms energy from one form to another is called a transducer.

Transducers are classified into:

  1. Active and Passive
  2. On the basis of principle used as Capacitive, Resistive, Inductive.
  3. Primary and Secondary
  4. Analog and Digital
  5. Transducers and Inverse Transducers.

What is sensor?

A sensor is a device which senses the presence or absence of energy; it measures a physical quantity and converts into a signal which can be measured by an instrument or an observer.Sensor is a device which responds with a change in physical phenomenon. The classification of sensor is based on conversion principle, based on quantity being measured and the technology used. The types of energy that can be sensed is classified as Mechanical, electrical, gravitational, thermal etc. Resolution in sensor defines its ability to detect a change in sensed element during measurement.

The sensing of any quantity is liable to errors. The two types of errors are Static error and Dynamic error.

  1. Static error: It is a type of error caused while sensing due to reading problems. The parallax of needle in meter scale is an example of this type of error. One major advantage of digital readouts is parallax error doesn’t exist.
  2. Dynamic error: This error is caused due to the difference in quantity as it really is and the amount to be measured, caused by the loading of measuring instrument itself. A typical example is a false voltage reading across a high- resistance potential divider with a voltmeter whose resistance is not high enough.

What are types of sensors?

Sensors are mainly classified into two as Active sensors and Passive sensors.

  • Active sensor : These type of sensors self generating and it does not require any external power supply. Photovoltaic cell, piezoelectric devices thermocouples are examples of Active sensors.
  • Passive sensor: These type of sensors requires an external power supply and are not self generating. A diaphragm used to convert the pressure is an example of passive sensor.

What is the difference between transducer and sensor?

The following are the differences between transducer and sensor or how is a transducer differ from a sensor.

  • A transducer is a device which convert one form of energy into some other useful form. While a sensor is a device which detects one form of energy and convert that data to electrical energy. So we can say that the sensors are, a type of transducer.
  • Sensor produces output based on the strength of the input physical quantity.
  • In sensors, the sensing element is the sensor itself. In transducers, other than the sensing element , a circuitry will be there; a signal conditioning element.
  • A sensor itself cannot give feedback to the system. While transducers can convert between any form of energy, it can give feedback to the system.
  • A sensor senses the changes in physical quantity in surrounding whereas Transducer converts the physical quantity into another form.
  • Is transducer a detector?
  • Sensors or detectors are a type of electrical transducers which can sense and convert energy (heat energy, light energy etc) from one form to another. Thus we can conclude that all sensors are transducers but all transducers are not sensors in all cases. Almost input transducers are sensors and output transducers are Actuators or Effectors.
  • Is Thermocouple a transducer or a sensor?
  • Peltier effect is the working principle of Thermocouple. The structure of thermocouple consists of two metallic ends joined together to form two junctions of different temperature. Peltier emf is generated due to the temperature difference in two junctions. A reference temperature is connected to one end for reference and unknown is connected to other end. Since it senses the temperature it is a sensor and it converts temperature into emf, hence it is a Transducer. Thermocouple acts as an active transducer.

These are the comparison between sensors and transducers.


Instrumentation & Control Engineer

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