Connecting a Modbus TCP Server To a DCS Client

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.

  1. Analyzer in explosion hazard area connects to gateway in safe area using fiber optic connection
  2. Gateway is connected using standard Ethernet cable to the analyzer’s control PC – which has Modbus TCP host
  3. Gateway is connected using serial connection to DCS / Modbus RTU client using serial connection