| 摘要 |
<p>PURPOSE:To decide the start of a network control device, by applying a power source to a call signal detecting circuit only in case a circuit has reversed in its polarity and at the same time the circuit voltage is within a range of the 1st and 2nd prescribed levels and with absence of a high level AC signal. CONSTITUTION:When a working power source is supplied from the terminals 111 and 112, a low voltage detecting part 12 works through a rectifier 17 and via a charging circuit consisting of an overvoltage detecting part 11, a resistance R and a capacitor C. Thus a switch 14 is controlled, and thus a power source is applied to a call signal detecting circuit 15 from a power source 13. Receiving a call signal from the center, the circuit 15 controls a connecting circuit 16 to connect the terminals 113 and 114 to the next data terminal 7. The rectifier 17, the part 11, the part 12, a CR charging circuit, the power source 13 and the switch 14 decides the fact that the line voltage is within a range of the 1st and 2nd prescribed levels and with absence of an AC signal of a high level.</p> |
