Sensors

The purpose of sensors is to acquire information and to forward it in an evaluable format to the signal processing system. They are found in diverse tasks in technology, with different designs and operating principles. That is why it is important to categorise them. Sensors can be classified according to

• operating principle (optical, inductive, mechanical, fluid, etc.),

• measured variable (displacement, pressure, distance, temperature, ph value, luminous intensity, presence of objects, etc.) or

• output signal (analogue, digital, binary, etc.), to name just a few methods.

The sensors used most frequently in automation technology are those with digital outputs as they are much more immune to interference than those with analogue outputs. Digital controllers can also use the signals from these sensors directly without first having to convert them into digital signals by means of so-called analogue-digital converters as is the case with analogue signals.

The sensors used most frequently in industrial automation are the so-called proximity sensors that determine the presence (or approach) of a workpiece.

Proximity sensors

Proximity sensors are non-contacting and therefore have no external mechanical actuating force. As a result they have a long service life and are very reliable. A distinction is made between the following types of proximity sensor:

• Sensors with mechanical switch contact – Reed switches

• Sensors with electronic switch output – Inductive proximity sensors – Capacitive proximity sensors – Optical proximity sensors