| 摘要 |
PURPOSE:To prevent the whole system from being stopped when an abnormality is generated by always monitoring a branch light outputted from a branching device, deciding that a terminal equipment is abnormal, when lighting has continued for the time which cannot be continued logically, and detaching it from a transmission line. CONSTITUTION:When a light emitting element 11 is lighted, a branch light is outputted from a branching device 14. This branch light is converted to an electric signal by a light receiving element 15. The continuation time of this signal is counted in a monitoring circuit 16. When its count time has exceeded the time which is set, based on the longest lighting time of the light emitting element at a normal time, a detaching command signal from a transmission line flows to a terminal 13 from the monitoring circuit 16. |
