| 摘要 |
PURPOSE:To improve reliability by attaining a fail-safe function by forcibly closing a photoshutter by a recovery signal from a terminal station even when the driving system of a supervising circuit gets out of order. CONSTITUTION:Discrimination signals (supervisory signals) characteristic to relays are received from the terminal station, and consequently photoswitch 8 is turned on to send back the above-mentioned signals from the up transmission line to the down transmission line. Photoswitch 8 has two photoshutter plates 11 and 12 forming a light passing window and recovery springs 13 and 17 are so provided that while shutter plate 11 is normally open, shutter plate 12 is normally closed. Then, the above-mentioned supervisory signals drive the 1st and 2nd driving coils 10 and 14 to close the above-mentioned two shutter plates and to turn on photoswitch 8, constituting a light sending-back circuit. In case that the 1st or 2nd driving system gets out of order and photoswitch 8 stays open in consequence, a recovery signal is separately sent out of the terminal station to force the photoswitch to close. |
