Transducer

A transducer is a device that converts one form of energy 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.).

Types of Transducers

Active Transducers

Active transducers convert energy directly from one form to another. They require no external power source to operate. For example, a thermocouple converts a temperature differential directly into an electrical voltage.

Passive Transducers

Passive transducers produce a change in some passive electrical quantity, such as capacitance, resistance, or inductance, as a result of stimulation. These usually require additional electrical energy for excitation.

Sensors

A sensor is a transducer whose purpose is to sense (i.e. detect) some characteristic of its environs; it is used to detect a parameter in one form of energy and report it in another, often an electrical signal. For example, a pressure sensor might detect pressure (a mechanical form of energy) and convert it to electrical signal for display at a remote gauge. Transducers are widely used in measuring instruments.

Actuators

An actuator is a type of motor that is responsible for moving or controlling a mechanism or system.

It is operated by a source of energy, typically electric current, hydraulic fluid pressure, or pneumatic pressure, and converts that energy into motion. An actuator is the mechanism by which a control system acts upon an environment. The control system can be simple (a fixed mechanical or electronic system), software-based (e.g. a printer driver, robot control system), a human, or any other input.

Bidirectional

Bidirectional transducers convert physical phenomena to electrical signals and also convert electrical signals into physical phenomena. Examples of inherently bidirectional transducers are antennas, which can convert conducted electrical signals to or from propagating electromagnetic waves, and voice coils, which convert electrical signals into sound (when used in a loudspeaker) or sound into electrical signals (when used in a microphone). Likewise, DC electric motors may be used to generate electrical power if the motor shaft is turned by an external torque.

Ideal Transducer Characteristics

• High Dynamic Range
• High Linearity
• High Repeatability
• Low Noise
• Low Hysteresis

Applications

Transducers are used in electronic communications systems to convert signals of various physical forms to electronic signals, and vice versa. In this example, the first transducer could be a microphone, and the second transducer could be a speaker.

• Electromagnetic:
  • Antenna – converts propagating electromagnetic waves to and from conducted electrical signals
  • Magnetic cartridge – converts relative physical motion to and from electrical signals
  • Tape head, Disk read-and-write head – converts magnetic fields on a magnetic medium to and from electrical signals
  • Hall effect sensor – converts a magnetic field level into an electrical signal
• Electrochemical:
  • pH probes
  • Electro-galvanic fuel cell
  • Hydrogen sensor
• Electromechanical (electromechanical output devices are generically called actuators):
  • Accelerometer
  • Air flow sensor
  • Electroactive polymers
  • Rotary motor, linear motor
  • Galvanometer
  • Linear variable differential transformer or Rotary variable differential transformer
  • Load cell – converts force to mV/V electrical signal using strain gauge
  • Microelectromechanical systems
  • Potentiometer (when used for measuring position)
  • Pressure sensor
  • Strain gauge
  • String potentiometer
  • Tactile sensor
  • Vibration powered generator
• Electroacoustic:
  • Loudspeaker, earphone – converts electrical signals into sound (amplified signal → magnetic field → motion → air pressure)
  • Microphone – converts sound into an electrical signal (air pressure → motion of conductor/coil → magnetic field → electrical signal)
  • Pickup (music technology) – converts motion of metal strings into an electrical signal (magnetism → electrical signal)
  • Tactile transducer – converts electrical signal into vibration ( electrical signal → vibration)
  • Piezoelectric crystal – converts deformations of solid-state crystals (vibrations) to and from electrical signals
  • Geophone – converts a ground movement (displacement) into voltage (vibrations → motion of conductor/coil → magnetic field → signal)
  • Gramophone pickup – (air pressure → motion → magnetic field → electrical signal)
  • Hydrophone – converts changes in water pressure into an electrical signal
  • Sonar transponder (water pressure → motion of conductor/coil → magnetic field → electrical signal)
  • Ultrasonic transceiver, transmitting ultrasound (transduced from electricity) as well as receiving it after sound reflection from target objects, availing for imaging of those objects.
• Electro-optical (Photoelectric):
  • Fluorescent lamp – converts electrical power into incoherent light
  • Incandescent lamp – converts electrical power into incoherent light
  • Light-emitting diode – converts electrical power into incoherent light
  • Laser Diode – converts electrical power into coherent light
  • Photodiode, photoresistor, phototransistor, photomultiplier – converts changing light levels into electrical signals
  • Photodetector or photoresistor or light dependent resistor (LDR) – converts changes in light levels into changes in electrical resistance
  • Cathode ray tube (CRT) – converts electrical signals into visual signals
• Electrostatic:
  • Electrometer
• Thermoelectric:
  • Resistance temperature detector (RTD) – converts temperature into an electrical resistance signal
  • Thermocouple – converts relative temperatures of metallic junctions to electrical voltage
  • Thermistor (includes PTC resistor and NTC resistor)
• Radioacoustic:
  • Geiger–Müller tube – converts incident ionizing radiation to an electrical impulse signal
  • Receiver (radio) converts electromagnetic transmissions to electrical signals.
  • Transmitter (radio) converts electrical signals to electromagnetic transmissions.

See also

• Horn analyzer
• List of sensors
• Tactile sensor

References

• Agarwal, Anant. Foundations of Analog and Digital Electronic Circuits.Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 2005, p. 43.

External links

• Introduction to Closed Loop Hall Effect Current Transducers
• Federal Standard 1037C, August 7, 1996: transducer
• A sound transducer with a flat flexible diaphragm working with bending waves