The distributed control system (DCS) has been used since the mid 70s, while the programmable logic controller (PLC) is slightly older. Some early installations still use microprocessors that predate the original personal computers. The ARC Advisory Group, Dedham, Mass., estimates that more than $65 billion worth of DCS installations are approaching (and in many cases, exceeding) 20 years in service—and this doesn’t include other control platforms such as PLCs or supervisory control and data acquisition (SCADA) systems.
So, industry faces an enormous challenge in replacing these computer-based systems. And, of course, doing so poses a substantial challenge in justifying the investment, managing the risk, and executing the project with minimal impact to cash flow.
As with most investments, project-justification for control-system replacement or migration should consider two key factors: risk reduction and lost opportunity.
The risk elements associated with control systems are similar to those of many computer-based systems. An unscheduled production outage because the normally reliable control system fails can prompt an incident that poses high risks to people, production and facilities and also might lead to potential environmental violations and damage to reputation—all the typical risk matrix impact or consequence dimensions.
