Proximity sensors are sensors that detect when a target object such as a metal has approached (or receded), without making direct contact with the object. Principle of high-frequency oscillation type: The detection coil located at the front end of the sensor produces a high-frequency magnetic field. When an object (metallic) approaches this magnetic field, induced currents flow in the metal, causing thermal loss and resulting in the reduction or stopping of oscillations. This change in state is detected by an oscillation state sensing circuit which then operates the output circuit.
As the sensor head contains only the emitting and the receiving elements, its size can be made small. Further, the sensitivity adjustment can be done from a remote place.
Since the amplifier is built-in, just connecting the DC electric power supply can provide a Non-contact output.