| 摘要 |
PURPOSE:To perform a connection test of each subscriber line, by connecting a test circuit containing an oscillating circuit, a filter and a monostable multivibrator with 1:1 correspondence or in common to a subscriber line circuit. CONSTITUTION:A connection test relay RLY is provided between a subscriber line TEL LINE and a subscriber line circuit LINE to perform switching between the normal and connection test modes. In a connection test mode, an oscillator OSC is connected to the line A of the line TEL LINE to transmit an AC signal of a fixed frequency. This AC signal is transmitted through a filter FIL which extracts only the component of the frequency transmitted from the line A and then supplied to a monostable multivibtator MM which has a slope several times as much as said frequency. If the output of the MM has a high level of potential, a normal connection is detected. While a non-connection or a fault such as a cut of the TEL LINE is detected if the output of the MM has a low level of potential. |
