The Process Behind Inductive Proximity Sensors

Position can be determined via one of two ways—either by determining ‘distance’ (the length of separation between two points) or by ‘rotation’ (angular movement). Sensors that are positional in nature can detect the movement of an object using linear sensors that employ the distance method or through rotational sensors that compute for rotation.

One type of positional sensor is the “Linear Variable Differential Transformer (LDVT), an inductive-type sensor that functions similar to the AC transformer when it comes to measuring movement. A common type of inductive positional sensor is the Eddy current sensor, which is mainly used to detect objects in close proximity. Due to this characteristic, Eddy sensors earned the more popular moniker ‘proximity sensors’.

Eddy current sensors are non-contact inductive positional sensors that detect current via a magnetic field with the reed switch acting as the simplest magnetic sensor. This type of sensor employs a coil that’s wound around an iron core within an electromagnetic field to create an inductive loop.

Inductive proximity sensors operate under the principle of Faraday’s Law of Inductance. When a ferromagnetic material such as a plate or screw is placed within the Eddy current field generated around the sensor, the coil’s inductance varies significantly. The sensor’s circuit detects this variation and thus produces an output voltage.