| 摘要 |
PURPOSE:To detect a fault surely within a time nearly twice the polling period at most by utilizing one of terminal devices of polling system to detect a fault of a transmission system. CONSTITUTION:An interface section IN of a system supervisory terminal device T0 receives a polling signal and when a terminal device address included in the polling signal is coincident with the own address, a pulse signal is outputted. The pulse signal is inputted to a timer circuit TM as a reset start signal and a time-up signal is outputted after a set time is elapsed from the timer circuit TM. When the time-up signal is inputted to an alarm circuit AL, it is discriminated as a fault of a transmission system and an alarm is raised. The setting time of the timer circuit TM is set to a value (e.g., twice of the polling period) larger than the polling period (nearly 2-3sec).
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