| 摘要 |
PURPOSE:To reduce the effect of disconnection of line, by the downward branch communication line in branch communication lines, auxiliary downward branch communication line, and managing communication line coupling the managing device coupled with the master station and the auxiliary managing device coupled with the auxiliary master station. CONSTITUTION:If there is open line in the branch communication lines 6, the master station 4 and the auxiliary master station 7 detect the decrease in the voltage of carrier mutually to confirm the open line of the lines 6 through managing lines 11, 12. The slave station 5 at remote location detects the lowering of carrier voltage of the downward branch communication line 8 and the slave station transmission/ reception section 20 is automatically subject to connection change to the auxiliary downward branch communication line 9. If there appears a slave station which does not respond to the call of the master station 4, the downward communication line termination resistor 33 is inserted to the line 8 with the instruction of the master station 4 at the slave station located just before it. Thus, the range in which the communication is enabled is extended at the disconnection of the line 6 and the effect of disconnection is decreased. |
