| 摘要 |
PURPOSE:To reduce the probability for the fault caused by the thunder, by connecting a telephone circuit to a key telephone only when it is used and separating the telephone circuit from the key telephone in case the circuit is not busy. CONSTITUTION:A relay 10 works when the telephone circuit is not busy and is recovered during the reception of signals by the incoming, busy and holding signals sent from an incoming detecting circuit 12 or a key telephone. The circuit 12 detects this recovery during the incoming and recovers the relay 10, and a relay contact 11 connects a telephone circuit 4 to the key telephone. Accordingly, the key telephone recovers the relay 10 through a signal line 8. When an incoming call responds, the line 8 transmits a busy signal. And the relay 10 continues its recovery. When the call is held, the line 8 transmits a holding signal to recover the continuously the relay 10. Then the signal of the line 8 is recovered by a ring-off, and the relay 10 works again to connect the telephone circuit to the circuit 12. |
