A sensor for a conductive coating delivery system subject to high voltage including a movable member, such as a pig received through a delivery line having a magnet and a sensor in the delivery system subject to high voltage including an optically polarizing device subject to magneto-optical change upon approach of the magnet generating a polarized light signal, optical fibers connected to the sensor receiving the polarized light signal connected to an electrical device situated remotely from the high voltage generating an electrical signal for controlling a valve, metering pump or the like.