Eddy current sensors (also known as inductive proximity sensors) use the physical effect of the quality change of a resonance oscillation circuit from which energy is drawn by means of eddy current losses in conductive materials. The proximity sensor combined with a condenser forms an LC resonant oscillating circuit which is excited to high frequency oscillations by an oscillator (e.g. 1 MHz). The electrical oscillations cause an electromagnetic alternating field to be emitted at the head of the proximity sensor. If an electrically conductive object is introduced into the field, eddy currents are produced in the object which draw energy from the field and attenuate the oscillation. The change in the amplitude of the oscillations is evaluated by a special electronic component (eddy current converter) and converted into an output signal which is proportional to the gap.
In contrast to the continuously measuring analog proximity sensor, simple inductive proximity switches assess only the existence or non-existence of a specific conductive object.
The eddy current produced by the object measured is very small and does not produce any appreciable heat or magnetic influence on the material. Inductive proximity sensors work contact-free, wear-free and, when in an appropriately encapsulated version, are less sensitive to vibration, moisture and (non) conductive contamination.