Realization of a fail-safe train wheel sensor using electromagnetic induction

A wheel detector is described as a method for detecting the approach of a train on a railroad without using any vehicle-mounted devices. Wheels of the train are detected as the change in the magnetic coupling between two coils located on either side of the rail. The coils are placed on one metal plate so that high sensitivity and reliability can be achieved. The wheel detector produces two fail-safe output signals having different characteristics when it fails. One output signal indicates the wheel detection state by the failure of any detector component, while the other indicates the wheel nondetection state by the failure of any detector component. Fail-safe window comparators are used to obtain these characteristics. The two binary output signals are related as mutually negative information and are produced as complementary output signals with double rails. The output signals allow fail-safe logic operations, including logic negations