A system of train detection is described which uses axle counting at two detection points, one at each end of the track section, imposing no special requirements on the railway track. These detection points are actuated by the wheels of the train, as many times as the number of axles in the train, and convey this information to a common electronic processing unit. The difference of the two counts provides a continuous indication of the clear or occupied state of the track section. The main features of the new design are that: (a) new techniques have been developed for the design of fail-safe circuits using TTL and ICs and applied to design of the system, and (b) the system has been made immune to interference from 25-kV AC electrical traction systems by means of suitable filtering techniques. A reliability and fault simulation study of the system has been carried out and the results show a negligible unsafe failure probability.
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