The basic idea of a transducer is that it takes one form of energy and converts it to another form. In most cases, a transducer will convert one energy signal form into another signal. In general, they will be used at important boundaries of measurement, control and automation systems. At these boundaries the electrical signals can be transformed from one physical to another, and to another signal. Examples of these signals include force, light, torque, energy, position and motion to name a few. Scientifically, the process whereby one energy form is converted into another form of energy is known as transduction.
Types of transducers
Below are some of the most common types of transducers and their application.
Active
An active transducer is one that is activated by some kind of external stimulus. In this situation, an additional energy source is not needed. Example of this type of transducer includes a piezoelectric sensor, a thermocouple and a photodiode.
Passive
With a passive transducer, there is a need for an external power supply. This power supply is called an excitation signal. The signal is then modulated to produce an energy output signal by use of a sensor. An example of this type of transducer is a thermistor. A thermistor does not create any electrical signal without and energy input but once an electric current passes through it, it creates a resistance. This resistance can then be measured by the detecting of the variations in the energy current across the thermistor.
Actuators
These are used to controlling or moving a system or mechanism. The energy source that operates an actuator can be hydraulic fluid pressure, mechanical force, pneumatic pressure or an electrical current. The energy is then converted into motion. In essence, an actuator is a device that can allow a control system to directly act upon its environment. The type of actuator can be varied including a fixed electronic or mechanical system, a human being, software-based such as a robot control system or printer driver, or many other types of inputs.
Sensors
With this type of transducer, the sensor allows a device to respond to stimulus or signals that it receives. A sensor and transducer are similar in application and the two names are often interchangeable. However, the term transducer can be used to describe various actuators, transistors and sensors.
Bidirectional
A bidirectional transducer is used to convert electrical signals into a physical phenomenon or a physical phenomenon into an electrical signal. A good example of a bidirectional transducer is an antenna. It converts the electrical signals to and from electromagnetic waves. Voice coils is another example that can convert sound into electrical impulses in the case of a microphone and electrical impulses into sound as is the case in loudspeakers. Furthermore, in a DC electric motor, the device can be used to create electric power by turning the motor shaft by an external torque force.
Ideally, transducers should have high repeatability and a high dynamic range. They should also produce low noise and low hysteresis.
Various applications
- Electromechanically or actuators – This type includes application such as air flow sensors, electro-active polymers, galvanometers and accelerometers. Furthermore, it can be used in rotary and linear motors. It is also used in vibration powered generators, tactile sensors and pressure sensors.
- Electromagnetic – The types of application that this type of transducer is often used for includes Hall Effect sensors, tape head and disk read-write heads as it converted the magnetic fields into electric signals, magnetic cartridges and antennae.
- Electrochemical – This includes applications such as the construction of pH probes, electro-galvanic fuel cells and hydrogen sensors.
