Ethernet based online process monitoring and controlling of a plant having RS-232 or RS-485 equipment

The most popular and traditional communication link among the plant equipment is either RS-232 or RS-485. Generally, these links are extended to a plant computer for Supervisory Control And Data Acquisition (SCADA) purpose. There are many benefits in upgrading such a system into an Ethernet enabled system (Reference 1). One can not only increase the number of devices that can be interfaced to a single computer, but also access the plant devices from multiple computers that are geographically distributed. The plant computer’s bus structures, such as ISA or PCI, and the availability of RS- 232 or USB ports will not be a constraint in increasing the number of serial port devices, once they are Ethernet enabled. A common method for Ethernet enabling is to replace the existing RS-232 / RS-485 equipment with those having built-in Ethernet. This is an expensive and time-consuming solution. A compromised solution will be to connect the plant computer to the LAN (Local Area Network). This method can help in the remote viewing of the plant data but online monitoring and controlling will not be possible. Further, if the plant computer fails, the remote monitoring will not be possible. A better technique in terms of cost, time-to-implement, redundancy and reliability will be to use a multi-channel Serial Device Server (SDS). The SDS accepts number of RS- 232/RS- 485 based devices and provides one Ethernet port through which they all can be accessed