Types of Transducers and Their Applications

The word transducer originates from the Latin word 'transducere', which means 'to lead across', or 'to transfer'.

By definition, a transducer is any instrument/device that is capable of converting one form of energy into another. The physical quantity may be anything such as temperature, pressure, acceleration, etc.

Most that are used today are electrical transducers, which typically convert a physical quantity into its electric equivalent (voltage, current, resistance, inductance, or capacitance).

In the following paragraphs, we will look at the various types and uses of transducers.

This is the most basic type of classification, in which each transducer is distinguished according to the physical quantity at its input which it is designed to convert to another quantity.

The following are a few examples that fall within this category:

► Temperature transducer (e.g. thermometer)
► Pressure transducer (e.g. microphone)
► Flow transducer (e.g. flowmeter)
► Displacement transducer (e.g. LVDT)

Different transducers can be categorized based on their individual modes of operation. This classification basically relies on the particular means that is used by the transducer to convert the physical quantity to the proportional electric one.

The following are the examples that fall within this category:

► Photovoltaic (e.g. solar cell)
► Electromagnetic (e.g. antennas)
► Piezoelectric (e.g. accelerometer)
► Mutual Induction (e.g. current sensor)

A transducer measures a physical quantity, and outputs proportional electric energy. For it to be able to perform this operation, it may or may not require an external source of energy.

Thus, accordingly, they can be broadly categorized into the following two types:

• Active Transducer
• Passive Transducer

Active Transducer
An active transducer is one which doesn't require an external source of energy for it to work. It uses the principle of conservation of energy, and is thus able to generate an electric quantity proportional to the physical quantity at its input.

The thermocouple is a typical example of an active transducer. It works solely on the principle that, in a continuous circuit made by joining two metals, if the two junctions are at different temperatures, a voltage proportional to the temperature difference can be measured across them.

Passive Transducer
A passive transducer is one that requires an external energy source in order to function. The capacitor microphone is one such example. In it, variation in sound pressure applied to a moving diaphragm gets converted to a proportional change in capacitance between two plates within it.

These two plates need an external source to charge them, without which, the microphone cannot function.

Transducers are used extensively in industries for measuring different quantities such as temperature, pressure, speed, acceleration, etc. The electrical signals provided by these transducers are processed by dedicated circuitry, and used for controlling and automating different large and small machines.

Transducers like speedometers, fuel-level sensors, crankshaft position sensors, parking sensors, etc., are commonly used in cars and other automobiles.

In modern homes/offices too, several different devices are used which make use of a number of different transducers for their working. These include, TVs/radios/Wi-Fi routers (antennas), washing machines (flow-sensors), air-conditioners (temperature sensors), etc.

Thermometers, pulse-rate monitors, stethoscopes, ultrasounds, sonograph machines, etc., are some of the examples of applications of transducers in the medical field.

Microphones, electric guitars, synthesizers, etc., and many other musical instruments too make use of transducers.