Position sensors are designed and built to be sturdy and resilient. They have to be able to withstand the extreme shock, vibration, and all the harsh elements associated with outdoor use. Moreover they also have to be able to cope with direct exposure to chemicals, dirt, moisture, sunlight, and electrical interference. Consequently most position sensors incorporate the following features:
Inductive proximity sensors work by analysing the changes in a resonant circuit which are caused by eddy current losses in conductive materials. An inductive proximity sensor is constructed from four essential components: a coil of wire wrapped in a ferrite core, an oscillator circuit, an evaluation circuit and an output circuit. When voltage is applied to the sensor, an oscillating current flows through the coil and radiates an electromagnetic field from the active face of the sensor. This field is directed and shaped by the ferrite core.
When an electrical conductor or metal target enters the electromagnetic field, eddy currents are drawn from the oscillator and induced into the target. These currents draw energy from the electromagnetic field. The subsequent losses in energy caused by the eddy currents are attributable to the conductivity and permeability of the target, the distance and position of the target, and the size and shape of the target.
When the metal target is positioned at a precise distance from the active face of the sensor, the energy loss caused by the eddy currents becomes so large that the amplifier cannot output sufficient energy to maintain oscillation and the magnetic field therefore collapses. The breakdown in oscillation is detected by the evaluation circuit, which then changes the state of the output circuit.