| 摘要 |
A train detection circuit is provided to determine whether a particular section or block of railroad track is occupied by a train. In one embodiment, a bias current generator is used to provide a low current signal that flows through the rails and through the wheels and axles of a railroad engine or car, such bias current ultimately being directed into a train detection circuit which measures the magnitude of the received bias current. If the bias current is greater than a certain magnitude, that is indicative of the particular block being occupied by a train. In second embodiment, a continuous pulse signal is directed into one rail, through a resistance bond, and through the other rail into a train detection circuit. The magnitude of this received pulse at the detection circuit will be quite small unless a train occupies the block. The received magnitude of the pulse signal can be compared to a predetermined threshold to determine the presence of a train in the block. The use of such pulse signals can also be used to determine from which direction a train enters this particular block, and can be provided with a high-pass filter to receive a clear high frequency pulse signal even in the presence of lower frequency signals.
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