A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact.
Proximity switches open or close an electrical circuit when they make contact with or come within a certain distance of an object. They are most commonly used in on-off valves feedbacks, manufacturing equipment, robotics, and security systems. There are four basic types: infrared, acoustic, capacitive, and inductive.
Inductive proximity switches sense distance to objects by generating magnetic fields. They are similar in principle to metal detectors. A coil of wire is charged with electrical current to produce electromagnetic field , and an electronic circuit measures this current. If a metallic part gets close enough to the coil, the current will change and the switch will open or close accordingly. The chief disadvantage of this type is that they can only detect metallic objects.
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