| 摘要 |
<p>In a train control signalling system, a wayside signal of an unknown code rate is detected and decoded on board the train to determine the code rate and derive the coded train control intelligence. The code rate is determined by counting the number of cycles of a known higher frequency which occur during one period of the unknown code rate. Before a train command signal is issued, a number of tests are performed to verify that the determination is accurate with no margin for error. The known higher frequency signal is passed through a tuned circuit to verify that it is within predetermined limits of its rated frequency. The counter that counts the cycles of the known higher frequency is tested to verify that it is reset to zero at required intervals. Verification is obtained that one and only one train control signal is obtained. The counting circuits and memory devices are cycled prior to each decoding operation to verify proper functioning. Each train control circuit is tested and none can operate unless the prior one in the chain responded properly. A train control circuit cannot remain operated unless it receives periodic confirmation signals.</p> |
