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, and an electronic circuit measures this current. If a metallic part gets close enough to the coil, the current will increase and the proximity switch will open or close accordingly. The chief disadvantage of inductive proximity switches is that they can only detect metallic objects. So, naturally you will have a switch bounce. Of course, you can implement debouncing techniques or another idea is to incorporate an inductive proximity sensor with a mercury switch, good luck finding that one. Also, if you have another inductive proximity sensor close by you could run into trouble, as well. Just for general knowledge see http://www.me.ua.edu/me360/PDF...itches.pdf for any other design solutions. What is really neat about that document is that it tells you how fast an inductive switch can switch. This means that you can use that information to help you make a timed debounce in firmware.