| 摘要 |
PURPOSE:To give an alarm if a terminal device is under working when the power supply is turned off and to prevent previously an inadvertent cut-off of a communication network, by using a 2-circuit/3-contact switch to the power supply of a communication controller in order to detect the working state of the terminal device. CONSTITUTION:It is possible to exclude a block system out of a communication network without affecting a transmission line 1 in case terminals 31-3n of a block are all not in use. When either one of these three terminals is used, it is impossible to turn off the power supply of a communication controller 2. Therefore a cut-off alarm for data communication control power supply is provided as shown in the diagram for each block. Thus the working state is detected for one of those three terminals if it is in use and when the power supply of the controller 2 is turned off. Then an alarm is delivered to prevent previously an inadvertent cut-off of the communication network. |
