| 摘要 |
PURPOSE:To attain a frequent test even if there are large number of subscriber lines and to relieve the trouble of a maintenance personnel by applying a high frequency signal of an oscillator at the exchange side to a subscriber line in a prescribed period and a consecutive time. CONSTITUTION:The oscillator 12 at the exchange side generates continuously a high frequency signal, which is turned on/off by a relay 19 of a timing circuit 13 at the exchange side and a receiver 20 at the exchange side starts the reception at the same time. If subscriber lines 2A,2B are normal, the output of the receiver 23 at the telephone set side goes to an H level, an output of the oscillator 31 at the telephone set side is turned on/off by a relay 30 of a telephone set side timing circuit 24 and the receiver 20 goes to an H level. If a fault such as an open line takes place in a subscriber line 2A or 2B or the both, the output of the receiver 20 goes to an L level. Then a counter 41 starts counting and if the counter 41 coutns'4' before a counter 36 counts '8', an output terminal A2 goes to an H level, the count of the counters 36,41 is stopped and an alarm lamp 44 is lighted.
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