RS Pro by Allied 8399875 Sensor Tester For Proximity Sensor/Switch 18VDC (2 x 9V Batteries) 35mA Overview RS Proximity Switch Test Unit Featured List: ABS cased unit designed primarily to test 3 or 4 wire NPN and PNP dc proximity switches Also capable of testing other 3 and 4 wire sensors with solid state outputs Connection via 3 spring loaded terminals LED status indication Suppli..