When connecting a Modbus TCP server to a Distributed Control System (DCS) client, sometimes a mismatch becomes apparent due to the DCS’s reliance on a non-TCP protocol (most often serial RTU). This is easily overcome by using appropriate gateway hardware. For example, B and B electronics (Ottawa, IL) offers MESR Modbus Gateway products with fiber Ethernet and built-in Ethernet pass through options available.
The topology of a plant spectroscopic analyzer deployed in an explosion hazard area and Modbus-TPC server connected to the DCS Modbus RTU client in this manner conforms generally to the following description.
- Analyzer in explosion hazard area connects to gateway in safe area using fiber optic connection
- Gateway is connected using standard Ethernet cable to the analyzer’s control PC – which has Modbus TCP host
- Gateway is connected using serial connection to DCS / Modbus RTU client using serial connection