Capacitive type proximity switch: A capacitive proximity switch is device that senses presence of metallic or nonmetallic objects. The internal circuit consists of an oscillator, threshold detection stage and an open capacitor formed by two metallic electrodes. The oscillator is inactive when target is away from the switch surface. When target is near to switch surface, change in the net capacitance formed by the switch open capacitor and the target. The circuit begins to oscillate and change in the oscillation amplitude is detected by threshold detection. When target is away from sensing surface, the output switching device is normally open. But when the target comes in close proximity of sensing surface, the change in oscillation amplitude is detected and output switching device is turned on.