Control system selection for a process plant: `Why a DCS may not be the answer´

It is noted that reduced process control budgets and powerful new programmable control systems have forced the design engineer to rethink his approach to process control. Traditional minicomputer-based distributed control systems can no longer be justified on process applications independent of their size. The authors describe a recent project which serves as a good example of this scenario. A combination of a limited control system budget and a highly flexible PLC-based system led to the reevaluation of the previously used approach to automatic process control systems. Alternative control system hierarchies were evaluated, comparing traditional approaches to new PLC based systems. A detailed review of the system selected is included