JPH0376871B

PURPOSE:To detect at least one of the breaks of a pair-stranded wires, by a pair-stranded wire break detecting unit composed of luminous element and light-receiving element installed each tacing the running pair-stranded wire. CONSTITUTION:A pair-stranded wire break detecting unit 1 is composed of luminous diode 2 and photo-transistor 3 as a luminous element with a running pair-stranded wire 14 between and when one or two wires are broken, light- receiving quantity of the photo-transister 3 is decreased as compared with the pair-stranded wire 14 running normally. This output is converted by a differen tial circuit 4 into change of light quantity and this output is changed to a DC component by a rectifying circuit 5 and later, amplified by an amplifier 6. Output of the amplifier 6 changes a parallel, connected CR circuit 7 and gets supply of the output voltage proportional to photoelectric change from the circuit 7. A break of wire is detected by comparing the output voltage with the constant voltage 8 by a comparator 9.