| 摘要 |
PURPOSE:To detect current accidents and troubles of a cable to predict future troubles, by comparing the transmission loss of a transmitted optical signal with plural discriminating levels to discriminate the state of the cable. CONSTITUTION:The optical signal taken out by a branching device 12 provided in the intermediate part of a cable 11 is supplied to an AND gate circuit 14 together with the signal from a timer signal generator 13 and return signals from a loss increase discriminator 23, an increase inclination discriminator 29, and an increase forecasting discriminator 31; and if input conditions are satisfied, the optical signal is supplied to a level operator 15. A level Ls is normally supplied from a memory 16 to the level operator 15, and a differetial level DELTAL between this level and a level Lp of the input signal is attained. This differential level DELTAL is compared with three discrimination level, i.e., a loss increase discriminating level Li, a considerable loss discrimiating level Lg, and an accident discriminating level Lt to discriminate the normal state, the occurrence of an accident due to break, or the occurrence of a trouble, and an alarm is indicated in accordance with them. |
