How Does An Inductive Proximity Sensor Work

An inductive proximity sensor can detect metallic objects that come close enough to the sensing side of the sensor. Do you wonder what an inductive proximity sensor working principle is? Well, I’m just going to tell you that, briefly.

Inside of an inductive sensor, there is an energy source to provide electrical excitation, an electronic oscillator consisting of an inductive coil made of several turns of very fine copper wire, and a capacitor for saving electrical charge. The inductive coil and the capacitor should have matched sizes in order to produce a stable, fixed frequency sine wave oscillation.

The oscillation produces an electromagnetic field in front of the sensor, because the coil is located right behind the “face” of the sensor. The technical name of the sensor face is “active surface”.

By entering a piece of conductive metal object into this electromagnetic field, a part of energy of oscillation will transfer into the metallic target. This transferred energy appears as tiny circulating electrical currents called eddy currents. That’s the reason why inductive sensors are sometimes called eddy current sensors.

The flowing eddy currents face electrical resistance of that metal, as they try to circulate. This will cause a small loss in power in the form of heat. This power loss would not be completely recovered by the sensor’s internal energy source. So, the amplitude of the inductive sensor’s oscillation decreases. Eventually, the oscillation decreases to the point that another internal circuit detects that the level has fallen below a pre-determined threshold. This threshold is the level where the presence of a metal target is definitely confirmed. Upon detection of the target by that other internal circuit, the sensor’s output is switched on.