Non-contacting extended range magnetic proximity sensor, not affected by dust or material build up, used to detect moving ferrous material up to 100mm away from the sensor. The WDA sensor can be used on bucket elevators to measure speed and alignment by sensing either the metal elevator buckets, or the ferrous bolts attached to plastic buckets. A more specialized use for the WDA switch is as a broken/slack chain detector on drag chain conveyors, or as a non-contact speed switch for screw conveyors.