| 摘要 |
PURPOSE:To facilitate the easy automatic switching of a circuit by providing a pilot circuit between a working station and a spare station and a main station and a switching station resepectively from the main station via the switching station and detecting the cut-off of a pilot signal due to a fault of the working station. CONSTITUTION:A main station 1, a switching station 2 and a working station 4 are connected by circuits L1-L3. A descending pilot signal P1 is oscillated 12 at the station 1 and detected by a coupler 33 of the station 3 via a switch 27 of the station 2. While ascending pilot signal P1 is oscillated 32 at the station 32 and detected by a coupler 13 of the station 1. In this case, a spare circuit L3 outputs the descending pilot signal P1 from an oscillator 22'' of the station 2, and this signal P1 is detected by the coupler of the station 3. While the ascending pilot signal P1 is transmitted from an oscillator 42 and detected by a coupler 23''. While the circuit L1 sends a pilot signal P2 of another frequency to a coupler 23 from an oscillator 12a and to the coupler 13 from an oscillator 22a and monitors them. When the circuit L2 is disconnected, a switch 2 is driven by the setection of a coupler 23' to secure connection between circuit L1 and L3. Thus the switching is facilitated with use of the pilot signals. |
