| 摘要 |
A permanent signal line lockout arrangement for crossbar switching systems is disclosed in which a silicon controlled rectifier (SCR) is inserted in series with the operate path of the line relay. When a customer lifts his handset to initiate a dial tone service request, the on-hook to off-hook transition triggers the SCR into conduction by means of a capacitive coupling network, and the line relay operates through the SCR. When a permanent signal condition is detected, the line is connected to a permanent signal holding trunk that is modified to remove the holding ground from the sleeve lead. Removal of the ground releases the hold magnet which thereupon reconnects the line relay to the permanent signal line. However, because the capacitor coupling network became charged when the sleeve lead holding ground was present, the SCR is not retriggered by the on-hook to off-hook transient that results when the line relay is reconnected. The line is thus held out of service for the duration of the permanent signal condition without need to maintain any switching connection to a permanent signal trunk.
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