Proximity switches

A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor's target. Different proximity sensor targets demand different sensors. For example, a
capacitive photoelectric sensor might be suitable for a plastic target; an inductive proximity sensor always requires a metal target.The maximum distance that this sensor can detect is defined "nominal range". They are used in alpha lubricator for finding the direction of rotation of crankshaft, encoding angle and also for finding rpm. there is also Inductive proximity switch for feed-back signal for control of piston movement inside alpha lubricators.