| 摘要 |
PURPOSE:To make it possible to measure accurately the guard delay time by detecting the state change of a subscriber's line by combining a received-signal stage with a transmitted-signal stage. CONSTITUTION:In a subscriber's circuit, received signal RD from a subscriber's line after level-converted by receiver 8 is sent to scanning multiplexing part 13 while a signal before passing through driver 9 for level conversion is selected as transmitted signal SD to the subscriber's line by selector circuit 10 and sent out to part 13. The selection of selector circuit 10 is put into effect by selective gate signal 11 from scanning counter part 12. Multiplexing part 13 multiplexes signals RD and SD by circuit number 14 corresponding to circuit coordinate from counter part 12 and then sends them to scanner circuit part 15. By number 14, circuit part 15 extracts corresponding signals RD and SD to detect the signal state. At this time, if signal RD has polarity A and signal SD changes in state from polarity Z to A, a time measurement is immediately started for supervision over the guard delay time. Even if SD has polarity A and RD changes from Z to A to the contrary, the same operation is done. |
