| 摘要 |
A system for signalling the fact that the fuses and limiting diodes in the connecting circuits of telephone lines are defective. Use is made of the rest supply resistors already present in the connecting circuits and the loop detector which is normally used for detecting calls. The fuses and limiting diodes are connected in such a way that a defect causes the loop detector, which is constructed as a differential voltage detector, to signal a call.
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