| 摘要 |
PURPOSE:To prevent missing data, by providing two timers to exclude the ''momentary disconnection'' and ''momentary disconnected input'' of input having the reset terminal and eliminating the unnecessary operation of line switching due to deterioration of the transmission line. CONSTITUTION:The timer 22 having the reset terminal R (to have the output of the NOT circuit 23) in timer time T1 to which the detection signal of the detector 21 detecting the subcarrier input fed to the terminal station B via the normal line 7 from the terminal station A, and the timer 24 having the reset terminal R (to have the signal from the detection circuit 21) in timer time T2 to which the signal from the detection circuit 21 is fed via the circuit 23, are provided. Further, the timer 22 is active with the input disconnected, and the timer 22 is reset when the input is normal before the time-up of the timer 22. When the timers 22, 24 are at time-up, the timing generator 25 produces clock pulse and the input state at that time is stored in the memory 26, and if the input disconnection is stored, for example, the relay coil 10a of the line switch 10 is energized and the relay switch 10b is switched to the spare side. |
