Non contact isolated current detector

Abstract

A receiver for sensing track currents includes a toroid coupled to the track rails via a single conductor. The toroid has an air gap in which a linear Hall sensor is inserted. The voltage of the Hall sensor is applied to signal processing circuitry including a low pass filter, amplifier and level detectors. In one embodiment of the invention comprising a track occupancy detector, second and third windings coupled to the toroid are selectively energized from a potential source to provide MMF's in the toroid of one and another polarity, and of a level less than the MMF provided by an occupied track section. The amplifier includes first and second channels for amplifying signals of opposite polarities. Each channel of the amplifier is coupled to a pair of level detectors, one of the level detectors in each pair is a vital level detector with the threshold set at about 50% of the threshold of the other level detector in the pair. A lack of occupancy is indicated when, during normal operation, level detectors trip in pairs. Lack of failures is checked by opening the conductor to the track rails and sequentially energizing the second and third conductors, and noting that one level detector in each pair trips in response to energization of the second or third conductors, respectively. Another embodiment of the invention is used as an approach detector by comparing current level in the rails with a fixed threshold, as current increases above the threshold an approach indication is given.