| 摘要 |
PURPOSE:To prevent a communication fault from occurring, by detecting degradation of the light emitting element of the optical transmitter of the preceeding station by respective node stations, which constitute an optical communication loop network, and a supervisory control station to transmit an alarm signal. CONSTITUTION:In each node station and a supervisory control station, the optical signal from an optical signal input terminal 10 is converted to an electric signal in a light receiving part 1, and the signal is taken out to an output terminal 1 through an amplifier 3 and a waveform shaping circuit 4. A part of this signal is applied to a light receiving level monitor part 7 through a peak-to-peak value detecting circuit 6 and an automatic gain adjusting circuit 5. At this time, since the photodetector has the characteristic changed by temperature, it is corrected by a temperature correcting circuit 8. When the photodetector is degraded and the level is lowered in a certain degree, an alarm circuit 9 transmits an alarm to an alarm output terminal 12. The time slot issued always for monitor is provided with one bit for insertion of the local address and the level alarm to transmit this alarm. |
