| 摘要 |
PURPOSE:To realize the change-over between a presently used terminal control device and a spare one with a simple constitution, by providing a contact which switches a terminal device and internal crossover wire and a guard line which controls the operation of a driving circuit, to a change-over device connected to a terminal controlling device. CONSTITUTION:When a terminal controlling device TC1 is equipped as a stand-by device, the present/stand-by change-over switch of a change-over driving circuit corresponding to the device TC1 is depressed. When the switch is depressed, a contact e131 in a change-over device EC1 connects a crossover wire IL11 to the device TC1. Other terminal controlling devices TC2-TCn are connected with terminal devices TA2-TAn, respectively. When a trouble occurs in the device TC2 and the present/stand-by change- over switch of its change-over driving circuit is depressed, a contact e232 is driven and the device TC2 is switched to the stand-by device through a common crossover track (such as IL11, CL1, etc.). Since a guard wire is earthed at this time, the other present/ stand-by change-over switches do not work even when the switches are depressed, and therefore, wrong connection of other terminal devices to the stand-by device is surely prevented. |
