| 摘要 |
PURPOSE:To compensate automatically a drop in received signal voltage by increasing a transmission output for a specific time when the leak current of a low frequency signal larger than a specific value is detected. CONSTITUTION:A voltage induced between a cable run 1 and a grounding point (E2) by applying a sent signal of low frequency to the cable run is denoted as (e) and the received voltage of a receiver 7 is denoted as V. Then this received voltage V becomes lower because of increases in grounding resistance (r) and electrostatic capacity (c) to the ground and a decrease in ground insulation resistance R. Further, a feedback current (i) based upon the low-frequency signal voltage (e) fed back to a grounding line 1 increases as a leak current (i) as the parallel impedance of the ground insulation resistance R and electrostatic ground capacity decreases. Consequently, the output of a current transformer which passes through the grounding line 1 is applied to a detecting circuit 10 and applied to the system consisting of a filter F, a rectifying circuit DET, and a comparing circuit COMP for a reference value i0; when the output (i) of the filter F increases above the specific value i0, the transmission output is increased to compensate the drop in the received voltage. |
