| 摘要 |
PROBLEM TO BE SOLVED: To provide a security guard terminal which will not malfunction due to noise or the like, and can identify communication infrastructures. SOLUTION: A polarity inverter 30 including a capacitor 33 and a current detector 20 (or 50) are connected to lines L1-L2. The polarity inverter 30 has a controller 13 for controlling the inversion of the connection polarity of the capacity 33, with a specified period to charge and discharge it with a voltage applied between the lines L1-L2. An inter-line voltage controller 40 is provided for checking the voltage between the lines L1-L2, to identify a communication infrastructure (ISDN, telephone circuit or PBX circuit and the like). COPYRIGHT: (C)2004,JPO
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