This type of setup uses the spindle/bit and the plate as a circuit. Not always the best idea. If you have a problem with use and it causes a fault you will most probably void the warranty.
Better idea is to make a Z axis setter with a switch inside similar to the limit switch. I use this type of switch on our flat bed router to re-set the z after machining the spoilboard.
Just utilize a redundant axis limit switch input.