Introduction of Transducers

A transducer is an electronic device that converts energy from one form to another. Common examples include microphones, loudspeakers, thermometers, position and pressure sensors, and antenna. Although not generally thought of as transducers, photocells, LEDs (light-emitting diodes), and even common light bulbs are transducers.
Efficiency is an important consideration in any transducer. Transducer efficiency is defined as the ratio of the power output in the desired form to the total power input. Mathematically, if P represents the total power input and Q represents the power output in the desired form, then the efficiency E, as a ratio between 0 and 1, is given by:

E = Q/P

If E% represents the efficiency as a percentage, then:

E% = 100Q/P

No transducer is 100 percent efficient; some power is always lost in the conversion process. Usually this loss is manifested in the form of heat. Some antennas approach 100-percent efficiency. A well-designed antenna supplied with 100 watts of radio frequency (RF) power radiates 80 or 90 watts in the form of an electromagnetic field. A few watts are dissipated as heat in the antenna conductors, the feed line conductors and dielectric, and in objects near the antenna. Among the worst transducers, in terms of efficiency, are incandescent lamps. A 100-watt bulb radiates only a few watts in the form of visible light. Most of the power is dissipated as heat; a small amount is radiated in the UV (ultraviolet) spectrum.


Classification of Transducers:

There are several ways in which you can classify transducers that include but not limited to the role of the transducer, structure of the transducer or the phenomena of their working.

Let us see the classification of transducers based on the following three ways:

Physical Effect
Physical Quantity
Source of Energy

Classification based on Physical Effect:

The first classification of Transducers is based on the physical effect engaged to convert the physical quantity to electrical quantity. An example, is the change in resistance (physical quantity) of a copper element in proportion to the change in temperature.

The following physical effects are generally used:

Variation in Resistance
Variation in Inductance
Variation in Capacitance

Classification based on Physical Quantity:

The second classification of Transducers is based on the physical quantity converted i.e. the end use of the transducer after the conversion. For example, a Pressure Transducer is a transducer that converts pressure into electrical signal.

Following is small list of transducers classified based on the physical quantity and corresponding examples

Temperature Transducer – Thermocouple
Pressure Transducer – Bourdon Gauge
Displacement Transducer – LVDT (Linear Variable Differential Transformer)

Classification based on Source of Energy:

Transducers are also classified based on the source of energy. Under this category, there usually two types of transducers:

Active Transducers
Passive Transducers

Active Transducers:

In Active Transducers, the energy from the input is used as a control signal in the process of transferring energy from power supply to proportional output.

for example, a Strain Gauge is an Active Transducer, in which the strain is converted into resistance. But since the energy from the strained element is very small, the energy for the output is provided by an external power supply.

Passive Transducers

In Passive Transducers, the energy from the input is directly converted into the output. For example, a Thermocouple is a passive transducer, where the heat energy, which is absorbed from input, is converted into electrical signals (voltage).