| 摘要 |
<p>1447511 Level crossing control GENERAL SIGNAL CORP 20 Aug 1973 [21 Aug 1972] 39293/73 Heading B7N In a level crossing arrangement two track circuits 12, 13 overlap at the crossing 11 and the road traffic crossing signal 19 is cleared when a train has left the crossing and the overlap section. The crossing signal is held clear in the absence of a train by pick-up of a relay 35 which is energized from an oscillator 24, supplying a square wave and D.C. signal, via gates 45-48 which are enabled respectively by the east track circuit receiver output RE, the west track circuit receiver output WE and by the absence of outputs on terminals SE and SW of hold circuits 26, 27 associated respectively with the east and west circuits. On entry of a train into the west circuit 12 the receiver output RW drops away thus closing gate 46 so that with cut-off of the oscillator signal relay 35 de-energizes to activate the crossing signal 19, and enabling gate 22 to supply the oscillator output to a hold OR gate 25 and to a gate 56 in a cross inhibit circuit 23. The gate 56, enabled by the absence of an output SE from hold circuit 26 applies the signal to OR gate 64 in hold circuit 27 which supplies an output SW which inhibits gate 57 in the east circuit part of the cross inhibit circuit, closes gate 48 and also enables gate 66 so that the output of hold OR gate 25 is supplied after immersion as a second input to OR gate 64 so that the hold circuit output SW is maintained until the train has cleared both track circuits. When the train enters track circuit 13 the output RE of the east track circuit receiver drops away so that gate 21 now supplies a second input to hold OR circuit 25 and when it leaves track circuit 12 the output RW of the west track circuit is restored thereby enabling gate 29 so that the output from gate 66 in hold circuit 27 is applied to buffer 32 to replace the signal still cut-off at gates 45 and 48 by signals RE and SW. The buffer supplies a signal to pick-up relay 35 and clear the crossing signal.</p> |
