Hello Frostywing. I'm very familiar with the Bombardier Global undercarriage. This uses a plethora of proximity switches to monitor door, leg and oleo extension. Each proximity switch had a steel 'target' that was sensed when in close proximity to the sensor. In effect it was like a microswitch but didn't need to physically move the switch. The target had to be very close to the proximity sensor - probably no more than 3-8mm for it to be sensed.
Of all the undercarriage malfunctions I was aware of (10 or so) all but one was caused by the steel target falling off. This meant, say, when the nose doors did close, the sensor couldn't see the target and so wrongly reported the doors as still being open!
Last edited by H Peacock; 11th June 2017 at 16:39.