Electricity and Control July 2023

CONTROL SYSTEMS + AUTOMATION

Designing distributed control systems to industry standards Best practice for the design of distributed control systems includes pursuing a standardised approach to configuring any DCS. For DCSs used to control sophisticated processes in many industries, the three most important factors to consider can be summed up as: standards, standards, and standards.

A distributed control system (DCS) serves as the hub of a processor’s operations and controls and mon itors key variables such as flow, applied tempera tures, pressure, level, and material conveying/handling. The human machine interface (HMI) of the DCS collects all the data from the production equipment and presents it in a user-friendly way for the operator. However, there are also multiple variables related to the type of equipment in use, the material being processed, the operator’s actions, and the control system. The DCS there fore needs to be designed to handle common, expected disturbances as well as unexpected anomalies in a pre dictable way. Designing a DCS application from scratch is like starting with a blank sheet of paper; it can be configured in almost any way imaginable. The important focus should be to de sign a robust system that delivers precise and predictable control. There is of course the risk for poor configuration – and this only accentuates the need to follow established stand ards and best practices in DCS design. A number of profes sional organisations and associations define the standards and best practices for process control systems. However,

most provide only general guidelines that can be applied to any distributed control system. Robert M Ard, Director of Applications Engineering at Valmet, says there are many other ways to achieve a level of standardisation in the programming and design to create a robust DCS. Valmet is a leading global developer and supplier of process technologies, automation systems, and services for the pulp, paper, energy, marine, and other pro cess industries. In January 2023, the company completed the acquisition of the D3 Control System from NovaTech Automation. “Standardisation begins with a commitment to a shared design philosophy, adoption of best practices, and the use of tools and techniques that reduce programming complex ity and time for similar processing equipment,” Ard says. Start with a well-defined design philosophy He suggests that every application configuration should begin with a well-defined design philosophy. Most DCS applications are created and maintained by teams of en gineers, so they should all be rowing in the same direction. “The best results can only be achieved when all contrib utors to the overall process control application follow the same best practices and techniques,” he says. When this is not the case, it will re

sult is unintended process errors and a system that is difficult to maintain. “Every engineer contributing to the application should strive to write their logic in the same way. The standard practices used should be well doc umented and taught to everyone re sponsible for the control system,” Ard adds. He says it would be an appropriate indication of a well-designed DCS ap plication if control systems engineers cannot identify the specific program mer by looking at the program logic or by observing its execution. One specific area of DCS design that illustrates the benefit of an es tablished, shared philosophy is alarm management. In process automation, an alarm is defined as an audible and/

The Valmet D3 interface displays real-time process information in a customer-oriented graphical HMI.

6 Electricity + Control JULY 2023