The basic function of an inductive proximity switch is to detect the presence of metal within a defined distance (SN) between the device and the metal. The operation is quite simple in that the device emits an electromagnetic field from the front or head. Any metal object entering causes a change in the field, which is then processed to provide a defined “on” or “off” output signal that can be further processed by control system devices like programmable logic devices, PLCs or turn on or off a warning LED light.

See related article, "Selecting Proximity Sensors for High Temperature Applications."