A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and control systems, where electrical signals are converted to and from other physical quantities (energy, force, torque, light, motion, position, etc.). The process of converting one form of energy to another is known as transduction.

Types

Sensors, actuators and transceivers

Transducers can be categorized by the direction information passes through them:

Active vs passive transducers

Passive transducers require an external power source to operate, which is called an excitation signal. The signal is modulated by the sensor to produce an output signal. For example, a thermistor does not generate any electrical signal, but by passing an electric current through it, its resistance can be measured by detecting variations in the current or voltage across the thermistor. Active transducers in contrast, generate electric current in response to an external stimulus which serves as the output signal without the need of an additional energy source. Such examples are a photodiode, and a piezoelectric sensor, photovoltic, thermocouple.

Characteristics

Some specifications that are used to rate transducers:

Applications

Electromagnetic

Electrochemical

Electromechanical

Electromechanical input feeds meters and sensors, while electromechanical output devices are generically called actuators):

Electroacoustic

Electro-optical

Also known as photoelectric:

Electrostatic

Thermoelectric

Radioacoustic