| 摘要 |
PURPOSE:To reduce the amount of hardware by providing a carrier detecting circuit in common, and to realize effective maintenance by selecting a circuit which recovers first as an in-use circuit when both circuits are faulty. CONSTITUTION:If a fault occurs to an (a)-side receiving line used as the in-use circuit, a multiplexing part 1 detects that to send out a fault detection signal LE to a switching signal detecting circuit 7. In this state, a carrier detecting circuit 3 detects the carrier of a (b)-side receiving line (stand-by circuit) to output a carrier detection signal ECD. When the carrier detection signal ECD and fault detection signal LE are both present, the switching signal detecting circuit 7 operates a switch control circuit 6 to switch circuits. If a fault occurs to the (b)-side receiving line as well, the switching is not carried out and if the (a)- side receiving line recovers first, the fault detection signal LE from the multiplexing part 1 is ceased and the (a)-side receiving line is used as the in-use circuit. |
