| 摘要 |
<p>PURPOSE:To immediately restore a metallic cable by detecting the fault of the metallic cable so as to use a conduction current thereby breaking an oxide film. CONSTITUTION:This device is provided with an input section 1 comprising a loop resistance detection circuit 1a for metallic cables S, R, an input changeover relay 1b, and an S/R changeover relay 1c selecting a speech current, resistance voltage conversion sections 2, 2' converting a loop resistance into a voltage, an amplifier sections 3, 3' comprising a low pass filter and a DC amplifier circuit, comparator sections 4, 4' comparing a reference voltage VO with an output voltage V1 of the amplifier sections 3, 3', a logic section 5 implementing input changeover control and transmission reception end changeover control, an output section 6 comprising one-shot monostable multivibrators 6a, 6b, 6c, an alarm display section 7 displaying, holding and counting alarm output signals h, h' of the comparator sections 4, 4' and a control signal conversion section 8 converting the alarm output signals h, h' into an alarm output earth signal (k). A change in the loop resistance is monitored and when the resistance exceeds a prescribed resistance, it is discriminated to be a defect and a prescribed conduction current flows for a prescribed time.</p> |
