Sensor and Transducer Technology

A sensor is a device that detects a physical quantity, such as temperature, light, pressure or position, and converts it into a signal that electronic systems can read. The broader term transducer describes any device that converts energy from one form to another; a sensor is a transducer used for measurement. By turning physical effects into electrical signals, sensors form the link between the physical world and the electronics that monitor or control it, and they appear in almost every measurement and automation system.

Sensors are grouped by the quantity they measure and by the physical principle they use. Temperature can be sensed by thermocouples, which produce a small voltage at the junction of two different metals, or by resistive elements whose resistance changes with heat. Force and pressure are often measured with strain gauges, whose electrical resistance changes slightly when the material they are bonded to is stretched or compressed. Light is detected by photosensitive devices, and magnetic fields by Hall-effect sensors, which produce a voltage in response to a field and are widely used to sense position and rotation.

Other sensors measure motion and displacement. Piezoelectric materials generate a voltage when squeezed and are used to sense vibration, force and sound. Gyroscopes sense rotation, and tachometers measure rotational speed, while specialised devices detect gas concentration, humidity or proximity. Because the raw output of a sensor is often small or nonlinear, it is usually amplified, filtered and calibrated by accompanying circuitry, a process called signal conditioning, before it can be used for an accurate measurement.

Frequently asked questions

What is the difference between a sensor and a transducer?

A transducer converts energy from one form to another; a sensor is a transducer used specifically to measure a physical quantity by turning it into an electrical signal.

How does a strain gauge work?

Its electrical resistance changes slightly when the material it is bonded to is stretched or compressed, so the resistance change indicates the applied force or pressure.

Why do sensors need signal conditioning?

A sensor's raw output is often weak or nonlinear, so it is amplified, filtered and calibrated before it can give an accurate, usable measurement.