| 摘要 |
PURPOSE:To protect an equipment connected to a communication line from a fault by the faulty voltage of a contacted power supply by sending a ringing to a line after the absence of contact of a commercial power line is recognized by a detection means. CONSTITUTION:When a call comes to a telephone set 1, the relay contact (t) of a TST 30 is operated in an LC 3 to draw a subscriber line 2 to a DET 33. If an AC 4 contacts the subscriber line 2, the DET 33 detects it to send a detection signal to a FF 34. The inverse of Q output of the FF 34 drives a transistor 35 to reset forcibly an R relay during the operation, then even when the relay contact (t) is restored by attending with the end of test, no ringing is fed to the subscriber line 2 from an RGG 36. Thus, the subscriber line 2 is tested and the absence of contact of the AC 4 is confirmed, then ringing is sent to protect the RGG 36 from an abnormal voltage.
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