Function, construction & technologies of sensors

How sensors work

A sensor converts the physical action to be measured into an electrical equivalent and processes it so that the electrical signals can be easily sent and further processed. The sensor can output whether an object is present or not present (binary) or what measurement value has been reached (analog or digital).

The main components of a sensor

A sensor consists of three main components:

(1) The sensing section contains the sensor itself which is based on a particular technology. The variety of technologies means you can select a sensor technology which fits your application.

(2) The processing circuitry converts the physical variable into an electrical variable.

(3) The signal output contains the electronics connected to a control system.

The various sensor technologies help you in detecting or measuring objects. Depending on the technology the sensors output a switching signal or a measurement value:

• Inductive sensors generate an electromagnetic field. This in turn generates eddy currents in objects made of metal. The sensor detects this change.

• Capacitive sensors generate a capacitive measuring field. An entering object results in a change to the measuring field. The sensor responds to this change.

• Photoelectric sensors (light curtains) always consist of an emitter and a receiver. There are diffuse, retro-reflective and through-beam types.

• Ultrasonic sensors send out a sound pulse in the inaudible range. The echo from the object is processed.

• Magnetic field sensors detect an external magnet. The field strength generated by the magnet is processed.

• Magnetostrictive sensors detect the position of an external magnet using propagation time measurement.