Re: proximity switches
Proximity switches sense the approach of a metallic machine part either by a magnetic or high-frequency electromagnetic field. Simple proximity switches use a permanent magnet to actuate a sealed switch mechanism whenever the machine part gets close (typically 1 inch or less). More complex proximity switches work like a metal detector, energizing a coil of wire with a high-frequency current, and electronically monitoring the magnitude of that current. If a metallic part (not necessarily magnetic) gets close enough to the coil, the current will increase, and trip the monitoring circuit. A good example of a simple proximity switch would be in an alarm systems door switch, an encapsulated reed switch is put on or in the door jamb and a magnet on or in the door, when the door gets close to the jamb the switch closes from the magnetic field
