| 摘要 |
PURPOSE:To release an alarm display by providing an alarm display releasing circuit on the telephone switchboard, and by means of a call signal in case when incoming for releasing the alarm display is made to said circuit. CONSTITUTION:When a special number dial related to the alarm display releasing circuit 10 is sent out to the incoming trunk 8 from the telephone set 7, the control unit 1 detects and discrimianates it, selects a call signal trunk 9, and connects it to the alarm display releasing circuit 10 through the network 2. The call signal is rectified by the diode bridge DB of the alarm display releasing circuit 10, and operates the signal detection relay R. It is detected by the current detection element PC that the contact (r) has been closed, an alarm display release signal RST is generated, and it is applied to the reset terminal RES of the flip-flop FF. Accordingly, it is stopped to send out an alarm display signal to the alarm display line 4. |
