Its not specifically looking for a ground its looking for a finish signal or something to close the circuit. On renishaw atlm units to test you command G31 and then just press on the plunger with your finger to watch the x bit change (forgot about that part) same goes with the spindle mounted probe units. Command the unit to turn on, command skip with an x move and feed rate turned down to 0, press cycle start and just lightly press on the ruby to see if its sending the finish signal feedback to the NC unit. You can also test it with a part if you know that you are, say, .09 from the edge of the part and command G91G31X.11F1. The ruby has a lot of play in the unit and .020 should be enough to get a skip feedback |