| 摘要 |
<p>PURPOSE:To effectively detect the abnormal mode of a line by impressing a voltage below a prescribed voltage to an operational amplifier having a resistance between two terminals connected to a two-wire type communicate on line and a resistance between one terminal and a reference power source. CONSTITUTION:Between the A terminal and the B terminal of a line monitoring circuit 1 having the A terminal and the B terminal connected to a two-wire type communication line (a), the resistance R1 of a resistance value 110kOMEGA, the resistance R2 of 820kOMEGA and the resistance R3 of 430kOMEGA for dividing the voltage of a the potential of the A terminal are connected, between the B terminal and the operational amplifier 11, the resistance R4 of 820kOMEGA is connected and between the B terminal and the reference voltage of -50V, the resistance R6 of 91kOMEGA is connected. Then, the zener voltage of a zener diode DZ1 in parallel to the resistance R3 is set to -9.1V, the zener voltage of a zener diode DZ2 between the B terminal of the amplifier 11 and a ground is set to -11V, and then, the voltage inputted to the amplifier 11 has V1<V2 only at the time of a normal mode.</p> |
