Proximity sensors are input devices that detect presence of an object without physical contact. Internal construction of inductive proximity switch is as shown in figure. It consists of a tuned circuit formed by coil and oscillator. When the switch is away from any metallic object the oscillator will oscillate. As soon as the metallic object comes near to the surface of the switch, oscillator gets loaded as eddy currents are induced in the metallic object. Drop in the amplitude of oscillations are detected by a threshold detect circuit and output stage. Normal sensing distance is 5mm.
Applications: 1) gear teeth sensing 2) RPM measurement 3) Object counting 4) Obstacle detection.