| 摘要 |
PURPOSE:To save remote control devices and supervisory control lines, by transmitting two pilot signals having different frequencies each other to transmission lines of two routes in parallel, and detecting a failure of the level of the pilot signals so as to switch the system. CONSTITUTION:The 1st pilot signal 1 and the 2nd pilot signal 7 are coupled 2 with the transmission lines via switch circuits 8, 9 and branched into the two routes at a hybrid circuit 3. The receiving level of the pilot signals through each transmitting line is monitored at monitor circuits 4 and 10 at the receiving end. In case of the failure of a line, the change in the 1st pilot incoming level is detected at the circuit 4, the receiving end is switched with a changeover switch 5 and alarm is transferred to an opposite station through the switch circuit 8. In switching the incoming route of the opposite station with the remote control, the 2nd pilot is interrupted manually, the opposite station detects it at the circuit 10 to activate the changeover switch 5 for the changeover of the receiving terminal. |
