| 摘要 |
PROBLEM TO BE SOLVED: To detect fault in a station side exchange even in the case that the fault is generated in a communication line on a terminal side and an insulation defect occurs. SOLUTION: When abnormality is generated in the communication line on the terminal side, a current passed through an input terminal L1A and a resistor 2 on one line side flows to the gate of a PUT(programmable unijunction transistor) 6, a voltage drop V2d is generated in the resistor 2 and the gate voltage of the PUT 6 is lowered by V2d. By a high resistor 8, a potential difference between the anode and gate of the PUT 6 also becomes almost V2d, the anode and cathode of the PUT 6 are turned ON and the route of the input terminal L1A, a resistor 7, the PUT 6, a diode 4, a resistor 5, an output terminal L1B and the fault point of the communication line is constituted. The anode and cathode of a PUT 14 are turned ON similarly on the other line side as well. Even when the current flowing in is a small current, the PUT 6 and the PUT 14 continue to be ON, a circuit to the fault point of the communication line is constituted through the PUT 6 and the PUT 14 and the fault is detected by the station side exchange.
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