| 摘要 |
PURPOSE:To make unnecessary a separation circuit in a loop start system, by detecting the earth utilizing the potential of its own negative power source only in a start up time to a station in a ground start system. CONSTITUTION:In an incoming, a ring line remains as a negative potential without changing, and a chip line changes from an open state to the earth, in the U.S. system. Since a current based on the potential change of the chip line passes through a current monitoring circuit 27, it is detected by a main detecting element. And the incoming is informed to a common control part. Next, when a start up operation for an outgoing is performed to the station, the earth is sent to the ring line by closing relay contacts gs<3>, gs<4> in principle. When the exchange side of the station is operated, and the earth is sent to the chip line, the potential change to the earth in the chip line can be detected by a current running from the current monitoring circuit 27 to the contact gs<4> and the negative power source 26 of the device.
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