| 摘要 |
PURPOSE:To catch securely a howler sound even when power fails, by providing a relay, which restores when an internal electric power source fails or when performing normal conversation, for a telephone set having a normal conversation circuit and public address conversation circuit. CONSTITUTION:When picking up a hand set while performing normal conversation, make contacts 3-5 of a hook switch are closed so that the conversation and catching a howler signal become possible irrespective of the short-circuit or open of a break contact 17 of a relay 16. In case of a public address conversation, if a lock type start-up switch is pushed down, its make contacts 7 and 8 are closed, and the relay 16 operates to open the break contact 17 if a DC electric power source circuit 11 is operating so that normal conversation or catching the howler signal can be performed. If power fails, a public address conversation circuit 9 does not operate, but the relay contact 17 is short-circuited to send the howler signal to a receiver 13 if the lock type start-up switch is forgotten to be restored under the condition so that it is securely known that the restoration is forgotten. |
