| 摘要 |
PURPOSE:To make unnecessary the closing of subscriber terminals corresponding to night direct telephone sets, by providing an incoming detection/loop closing circuit and night switching information tone transmission circuit at a subscriber terminal, transmitting the night switching information tone to the caller side through the detection of the first incoming call after night switching, and keeping the subscriber terminal at calling state thereafter. CONSTITUTION:A relay contact nt1 is provided at a main wire and a circuit to a main wire trunk COT, and a relay contact nt4 is provided for an extension telephone set TELA anda circuit to a subscriber terminal LLN, and relays nt2 and nt3 are used to connect the circuits. Separately, a night switching relay NT incorporating a relay NTA and a nighy switching key NTSW is provided to constitute a night switching trunk, and the following devices are provided additionally. That is, a resistor R, diode D, night switching detection relay X, and relay contact nt5 are connected to a circuit consisting of the subscriber terminal LLN and the extension telephone set, and the relay X, relay contact nt6 and sound source NTG are connected to the relay NTA. |
