DETECTING SYSTEM OF FAULTY AREA

PURPOSE:To realize a highly accurate detection even for a fault caused at a remote place in an optical cable transmission system, by giving a short circuit to a metallic conductor by means of a connection box and an optical repeater detected in the case of a fault and measuring the DC resistance at a transmission end office. CONSTITUTION:The optical signal of a regular code transmitted from a transmission end office 1' is monitored by an optical repeater 4'. When the regularity of the code is disturbed, a code rule monitoring circuit 29 of the repeater 4' produces the pulse to give a short circuit to an intermediate pair of metallic conductors 14 by means of a switch SW3. In case an optical fiber cable 13 at the front stage of the repeater 4' is broken, a switch SW2 is actuated by a large change of the voltage which is supplied to a photoelectric converting circuit 22 via an AGC circuit 27 to give a short circuit to the conductors 14. As a result, whether the repeater 4' or the cable 13 has a fault can be decided from the measured value of the DC resistance of the conductor 14 and at the station 1'.