| 摘要 |
PURPOSE:To attain economization by making it easy to set the same detection threshold level, by holding an input to a subscriber's line loop detecting circuit during call signal transmission at the same level with that to the subscriber's line loop detecting circuit during calling, disconnection and dial pulse reception. CONSTITUTION:When the loop of a subscriber's line is monitored with an electric current flowing through the tertiary winding of hybrid coil 11, a call signal is sent out through the intermittence of a sending relay and during the call signal transmission, an output to circuit 19 which detects the existence of the subscriber's line loop is varied by switching contact 23 of the relay for transmitting the call signal. During origination, disconnection and service other than the call signal transmission, it is held at the same level with an input to circuit 19, so that the subscriber's line loop can be monitored with the same detection threshold level. Therefore, while relays are not increased, this purpose can be attained by adding one resistance and by changing one of contacts of the relay for transmitting the call signal from a make contact to a transfer contact. |
