| 摘要 |
PURPOSE:To eliminate a need to make the transmission signal from a master station to a slave station dual in time series. CONSTITUTION:A master station 1 and slave stations 21, 2n-1, and 2n are connected like a loop by dual optical transmission lines 31 and 33, and transmission and reception signals are transmitted in opposite directions. When optical transmitters and optical transmission lines are normal, a signal A0 is transmitted to slave stations through an optical transmitter 42 and the optical transmission line 31 by one system, and response signals from slave stations are received as a signal B2 by an optical receiver 45; and if the response from slave stations to transmission of the signal A0 is not returned within a certain time, the system is switched to transmit a signal Ae to slave stations through an optical transmitter 44 and an optical transmission line 32. In the case of disconnection of both systems at a point A or B, signals are transmitted and received by transmission and reception in inverse directions on optical transmission lines. |
