| 摘要 |
PURPOSE: To monitor emergency telephone sets by separating them into plural groups by inverting the connection polarity to a pair of monitoring lines of the monitoring line connection terminal in an emergnecy telephone set and switching a power source for monitoring in an inversion circuit. CONSTITUTION: The side of a monitoring line 301 and the side of a monitoring line 302 are connected with the side of the monitoring line connection terminal 201 of emergency telephone sets 2-1 to 2-9 and the side of the monitoring line connection terminal 202 of the telephone set 2-1 to 2-9, respectively. The side of the line 301 is connected with the side of the terminal 202 of each telephone set 2-1 to 2-9. The side of the line 302 is connected with the side of the terminal 201 of the telephone sets 2-1 to 2-9. Next, a monitoring part 1 1 operates an inversion circuit 13, the polarity of a power source for monitoring to be supplied to the monitoring line 3 is inverted, and a negative polarity power supply and a positive power supply is supplied to the side of the line 301 and the side of the line 302, respectively. As a result, a diode 21 becomes conductive, power supply is supplied to monitoring controls CPU and PB from a constant current circuit via a constant voltage circuit and various kinds of controls are performed. As a result, because the telephone sets 2-1 to 2-9 are separately checked, sufficient current can be supplied. |
