| 摘要 |
PURPOSE:To detect a called party reply due to the polarity inversion of a line in distinction from the lockout due to power interruption of the line by providing two detection elements operated in a different polarity to the line. CONSTITUTION:Denoting the polarity of lines L1, L2 by +, - respectively at the initial state, a detection signal P1 from a photocoupler 11 as a detection element goes to 1 and a detection signal P2 from a photocoupler 12 goes to 0. Inverting the polarity of the lines L1, L2 by the called party reply, the signal P1 from the coupler 11 goes to 0 and the signal P2 from the coupler 12 goes to 1. Then in the case of denoting the polarity of the lines L1, L2 by -, + respectively at the initial state, the similar polarity inversion is applied. In case of the power supply interruption of the lines L1, L2, the signals P1, P2 go to 1. Thus, when the one coupler is moved from the operating state into the unoperating state and the other coupler is moved from the unoperating state into the operating state, it is detected as the called party reply due to the polarity of line and when both the couplers are in nonoperating state, it is detected as lockout.
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