The Choice between a Process Control Computer and Distributed Control for Industrial Processes

The hardware and software differences between commercially available process control computers and microprocessor based distributed process control systems are briefly examined. Each has a different set of capabilities and disadvantages arising from quite different system design philosophies and so for any given process control task one of these types of systems should perform significantly better than the other. Experiences involved during a recent process plant up-grading using a distributed control system are discussed with a view to aiding the decision making process of an engineer about to apply a microprocessor based instrumentation system. It is concluded that distributed microprocessor systems are appropriate for highly regimented processes requiring a high degree of security against control system failure. Computers may do a better job where process control requires a high degree of versatility or significant use of novel techniques and where the occasional system breakdown can be tolerated.