| 摘要 |
PURPOSE:To decide the normality of the line insulating resistance of a subscriber line by obtaining the condition to separate a telephone terminal from a subscriber and measuring a terminal transmission type resistance when the electric power source of a voltage lower than the forward voltage of the rectifying circuit in a telephone terminal, a direct current flows at a terminal transmitting type and the rectifier of the rectifying circuit is not conducted. CONSTITUTION:A measuring circuit 3 is provided with an electric power source VT having the voltage lower than the forward voltage of the rectifying circuit of an interface circuit 11, supplies the direct current through a resistance r2 to a terminal transmitting type, measures the voltage drop of the resistance r2 with a detecting circuit 31 and measures a terminal transmitting type resistance Z. Consequently, the circuit after a diode including an electricity receiving circuit resistance RP is separated and the terminal transmitting type resistance Z comes to be a line resistance RS and a line insulating resistance RL only. Since the line resistance RS is about 0-1KOMEGA and the line insulating resistance RL is usually about>=20 KOMEGA, the normality of the line insulation can be decided by measuring the terminal transmitting type resistance Z.
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