A major petroleum producer needed to interface a DeltaV Distributed Control System (DCS) from Emerson Process Management to a facilities automation system, which was based on popular, off-the-shelf industrial human-machine interface (HMI) software.
Design standards for the DCS system required that, in all interfaces to external systems, the DCS system be the master. This meant the DCS system would initiate all communications. The HMI system was designed to operate the same way, in that the HMI expects to be the master when connecting to its data sources. The customer utilized OPC server software solutions from Software Toolbox, in Matthews, N.C., to bridge the gap between the DCS and HMI systems.
First, the customer installed Software Toolbox's TOP Server Modbus Ethernet Slave OPC server on the same computer as the HMI-based Building Management System (BMS). Then, in the HMI system, personnel mapped all data points that were to be shared with the DeltaV DCS system (read or write) into points in the OPC server.
In the DCS system, the Modbus Ethernet Master interface was configured to connect to the OPC Server over Ethernet, using the open Modbus TCP protocol. When the DCS wants to read data from the HMI system, it reads the Modbus addresses in the OPC server that correspond to the data points mapped from the HMI into the OPC server. When the DCS wants to write data, it writes to the Modbus addresses in the OPC server. The OPC Server automatically updates the HMI with the new values.
The use of an open system based on OPC and Modbus generated significant savings in integration time and engineering for the user of the application. In addition to these savings, the open system made system checkout possible.
The prime contractor for the job was in Europe, with an integrator in the Middle East, a planned installation in the Middle East, and a system checkout planned in the United States. Through the use of open systems, all interconnections were planned ahead of time via e-mail correspondence between the parties.
At checkout, a technician skilled in the use of OPC and Modbus was contracted in the United States to attend the system checkout on behalf of the integrator from the Middle East. In one day, all interface points were tested and checked, saving the integrator the expense and time of traveling to the United States for system checkout.
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