Transducer and its classification

What is a transducer

The electrical transducer is a device which can be used to convert a non-electrical physical quality like temperature, sound or light… into an electrical signal such as voltage and current. It can also be described as a device which is capable to convert physical quantity into a proportional electrical quantity such as current and voltage. The transducer has two parts they are the sensing element and transduction element. The sensor is the sensing element and it will produce measurable response to change in physical conditions and the transduction element will convert the sensor output to suitable output form.

Transducers are usually electrical, electronic, electro-mechanical, electromagnetic, photonic or photovoltaic it can convert one form of energy to another form it converts the measurand to a usable electrical signal

What are the factors that must be considered while selecting a transducer

  • Sensitivity – it must be sensitive enough to produce detectable output
  • Operating range – it should maintain the range requirement and it must have a good resolution over the entire range
  • Accuracy– high accuracy must be assured
  • Avoid errors – transducer must maintain the input-output relation as described by the transfer function in order to avoid errors
  • According to operating principle – Mostly transducers are selected according to the operating principle used by them and the used operating principle could be resistive, inductive, capacitive, piezoelectric…
  • Transient and frequency response – it should meet the desired time domain specification like rising time, setting time, and small dynamic error
  • Loading effects – to avoid loading effects a transducer should have high input impedance and low output impedance
  • Environmental compatibility – the selected transducer must be compatible with the environmental conditions and it must maintain its input and output relation and must not break down
  • Avoid unwanted signals – the transducer should be able to avoid or less sensitive to unwanted signals and it should be highly sensitive to the desired signals

Classification of transducers

  • Active and passive transducer
  • Analog and digital transducer
  • On the basis of transduction principle used
  • The primary and secondary transducer
  • Transducers and inverse transducers
  • Resistive transducer

Active transducers

These transducers don’t need any external power source for its operation so it can be called as a self-generating type transducer and they operate under the energy conversion principle. So it does not require any external power source and produce an analog voltage or current when stimulated by some physical form of energy

Examples – thermocouple, photovoltaic cells, thermopiles, piezoelectric

Passive transducers

This type of transducer needs an external power source for energy conversion. Mostly a DC power supply or an audio frequency generator is used as an external power source and the variation in the resistance, capacitance, and inductance is the output signal in response to the quantity being measured.

Examples – thermistor, resistance strain gauge, differential transformer

Primary and secondary transducers

Certain transducers have mechanical as well as an electrical device, the mechanical device converts the physical quantity to be measured into a mechanical signal and such mechanical device is called as primary transducers and they deal with the physical quantity to be measured. The electrical device then converts this mechanical signal into a corresponding electrical signal such electrical signals are called secondary transducers

Transducers and inverse transducers

A transducer can convert non-electrical quantity into electrical quantity while an inverse transducer can convert electrical quantity into a non-electric quantity

Analog and digital transducers

In an analog transducer with the variation of input, there is a continuous variation of output. These type of transducers converts the input quantity into an analog output which is a continuous function of time examples are a strain gauge, thermocouple, and thermistor. In digital transducer with the variation of input, there is a digital or discrete type of output examples are a digital encoder, vibrating string transducer.

Resistive transducer

Resistive transducers are transducers in which resistance changes due to the change in some physical phenomenon

Potentiometer (resistive transducer)

This type of resistive transducer is used for voltage division, they consist of resistive element provided with a sliding contact and the sliding contact is called a wiper. A potentiometer uses electrical resistance as a means for measuring position.

Strain gauge (resistive transducer)

A strain gauge is a passive transducer which uses electrical resistance variation in wires to sense the strain produced by a force on the wire. It is a transducer which can be used to measure weight, pressure. The strain gauge converts the mechanical elongation and compression into a resistance change and the changes in resistance take place due to the variation in length and cross-sectional area of the gauge wire when an external force acts on it.

Thermistor (resistive transducer)

A thermistor is a type of resistor, thermistors are temperature-dependent resistors whose resistance varies significantly with temperature. Semiconductor thermistors have a negative temperature coefficient so when the temperature increases resistance decreases. Thermistors are widely used in inrush current limiters. Thermistors are composed of a mixture of a metallic oxide such as nickel, cobalt, copper, uranium, iron

Transducers according to the transduction principle

Capacitive transducer

Capacitive transducers are the capacitors with variable capacitance they are used for measuring linear displacement. In this transducer the capacitance change due to the change in some physical phenomenon into an electrical signal, capacitive transducer measure the displacement by measuring the change in capacitance.

Advantages of capacitive transducers

  • Operational force is less and they are very useful in small systems
  • Highly sensitive
  • It has great frequency response and it can measure both static and dynamic changes

Disadvantages of the capacitive transducer

  • Performance is affected by the dirt and other contaminations
  • Sensitive to temperature variations

Inductive transducer

These transducers work on the principle of magnetic induction, it may be self-generating or passive type. electrical generator principle is used in self-generating type, that when there is a relative motion between a conductor and a magnetic field a voltage is induced in the conductor and this relative motion between field and conductor is supplied by changes in the measured. a tachometer is an inductive transducer which converts speed or velocity into an electric signal.

Electromagnetic transduction

In this type, the measurand is converted to the voltage induced in a conductor by a change in the magnetic flux in the absence of excitation. These transducers are active transducers, change in flux is done by the motion between a piece of magnet and electromagnet

Types of transducer

  • Piezoelectric transducer

This is a special kind of sensor, and the main function of this transducer is to convert mechanical energy to electrical energy. And then electrical into mechanical energy It is used to detect the stick drum impact in electronic drum pads. it can be used as a knock sensor in automotive engine management systems for noticing knock of the engine.


It is used to measure pressure of the specific quantities like gas or liquids by changing the pressure into electrical energy its main application is amplitude sensing depth sensing, flow sensing, and leak testing these transducers can be used for generating electric power under the speed breakers on the highways of the roads where the force of the vehicle can be converted into electrical energy.


This is an electrical device that is used to convert the temperature of the device into another quantity like electrical energy pressure or mechanical energy then the quantity will be sent to the control device for controlling the temperature of the device. It is used to check the temperature of the air so that we can control the temperature of several control systems like air conditioning, heating ventilation and so on


This transducer will convert electrical signals to ultrasound waves. It can also be used to measure the distance of the sound based on reflection. By the help of this transducer, we can find areas which are hard to find like high pressure or high-temperature areas. This system uses 8051 microcontroller, power supplies, an ultrasonic transducer module that includes transmitter and receiver,

if any obstacle or any object is found that is detected by ultrasonic transducer, then it will reflect back from the object and transducer will receive these waves the time used by the transducer for transmitting and receiving the waves can be noted by considering the velocity of the sound then based on the sound velocity and by the help of microcontroller the distance is measured and will be displayed on the LCD display


Applications of transducer some are used in medicine as sonograph machines in the medical field and there are others which are used in music recording

  • Used to determine the movement of muscle which is called acceleromyograph.
  • Measures the load on the engines
  • Used to sense engine knock
  • It is used to measure the pressure of gas & liquid


post-graduate in Electronics & communication.

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