| 摘要 |
PROBLEM TO BE SOLVED: To surely secure signal transmission even when any abnormality occurs in a repeater by short-circuitting one transmission line, which is connected to the repeater, to the other transmission line when abnormality in the repeater is detected. SOLUTION: When power supply abnormality is not detected, a relay SW is turned on and the switching contacts of respective switches SW11, 12, 21 and 22 are located on the side of make contact as shown by a dotted line. A signal inputted from a transmission line L11 is outputted through a transmission line extending device 61 to a transmission line L12. When a monitoring circuit detects the power supply abnormality, in a power failure state, for example, the relay SW is switched into off state and the switching contacts of respective SW11, 12, 21 and 22 are switched to the side of break contact as shown by a real line. Thus, the detector system transmission lines L11 and L12 are turned into short-circuitting state through the switches SW11 and SW12, control system transmission lines are turned into short-circuitting state through the switches SW21 and SW22, a bypass route is secured and the signal transmission to the side of next step is prevented from being cut.
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