| 摘要 |
PROBLEM TO BE SOLVED: To discriminate a fault part, to facilitate maintenance and to monitor a transmission line during communication by providing a carrier monitor timer circuit which does not output a signal when a signal source breaks down but outputs the signal only when the transmission line breaks down. SOLUTION: A transmission monitor timer 15 for inhibiting continuous transmission for more than prescribed trainsmission time (t) is provided on a transmission-side 100. The carrier monitor timer circuit 16 for outputting the signal 17 when a reception carrier continuous for more than setting time (t) is provided for a reception-side. When a fault occurs in the transmission-side or an optical fiber 8, the light reception quantity of a receiver 9 reduces and an output signal 10 becomes unstable. the signal 17 is outputted when continuous time becomes setting time (t), the output signal 19 of a storage circuit 18 is kept, a lamp 22 is lighted, and reduction is displayed even if a carrier detection circuit 11 erroerneously recognizes the presence of the carrier and outputs a signal 12. A post-stage circuit stops the processing of the output signal 14. Then, setting time (t) is set to be considerably short and the transmission line can continuously be monitored even in regular communication. |
