| 摘要 |
PURPOSE:To stabilize operation, and also, to improve reliability by detecting whether a transmission signal exists in a transmission line or not, and detaching a line of a short circuit part by a normally closing switch of a relay. CONSTITUTION:When terminals 30, 40 are short-circuited and go to zero potential, outputs from transmission pulse detecting circuits 2, 21 annihilate, and capacitors C2, C21 are charged with charges accumulated in a capacitor C3. When the charged voltage of the capacitors C2, C21 goes to a prescribed value, a transistor TR2 turns ON, a relay A is operated by the charge of the capacitor C3 and a normally closing switch (a) is opened, and the voltage between terminals 10, 20 is released to the original voltage. When the short circuit state between the terminals 30, 30 is released, the output is generated again from the transmission pulse detecting circuit 21 by a transmission pulse from the other side of a loop-like transmission line, the transistor TR2 turns OFF, the relay A is released and the normally closing switch (a) is closed.
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