FACILITIES EQUIPMENT COMMUNICATION CIRCUIT

摘要

A communication circuit is realized which uses three wires, including a power supply, to provide an erroneous-connection protection, a long wiring, and a high-rate transmission. In a communication system using, as a shared wire, one of two AC power supply wires, a first constant current source is series connected, in a master station, with a master station transmission photo-coupler, a reception photo-coupler and a constant voltage diode in the named order from the positive side of the power supply to the negative side thereof serving as a reference, and a communication path, which extends from a node located between the transmission and reception photo-couplers, is wired through a relay to slave stations. In each of the slave stations, a circuit, in which a second constant current source and a slave station reception photo-coupler are series connected with a reference wire, is parallel connected, via a relay, with a photo-coupler so disposed as to short-circuit an output of the relay to the reference wire. The relay is controllably turned on when it is determined that a potential difference between the communication path and the reference wire becomes below a predetermined value.