RS485MS-2W Communications Module

The Model RS485MS-2W Communications Module serves two very important functions. From a communication network view, its primary purpose is to electrically isolate the communications network from the high voltages present in SymCom’s units and to convert the communications signals from the microprocessor’s 5-volt levels into RS-485 levels. The second function of the RS485MS-2W is to provide power to the RM-1000 remote monitor.

SymCom’s units are connected to high AC voltages with a fl oating ground circuit. As long as there are three balanced line voltages present, the resulting ground level will often be near case ground. However, if one phase is lost or if the line voltages become unbalanced, the fl oating ground may be as much as 480 volts above the case ground. The RS485MS-2W has two high speed optical isolation chips on the receive and transmit pins and a low speed optoisolator on the transmit/receive pin to isolate the communication network from the AC line voltages.

The signals from the microprocessor go through resistors to provide current limiting before connecting to the 9-pin external connector. Therefore, the 9-pin SUB D connector on the SymCom unit provides un-isolated CMOS signals and is NOT RS232 or TTL compatible.

The RS485MS-2W does not have support for four wire communications systems.