PLC or DCS: selection and trends

Abstract The PLC versus DCS argument has been around for quite a while. Some time ago, PLCs took on powerful, robust, third party, PC-based graphical operator interface packages known as SCADA. This expanded Man Machine Interface propelled the PLCs into areas where they could successfully compete with DCSs for similar control applications. Since then, automation engineers have struggled with a set of guidelines for using PLCs versus DCSs in batch operations and other applications. There is no clear answer to this issue. There are, however, decision tools, such as Kepner-Tregoe (K-T) that can be applied by engineers as a structured approach to decision analysis and system selection. Involvement in other factors, such as business environment, pressure to reduce project cost, validation or predicting new technology direction, all play a critical role for engineers in choosing between a PLC or DCS based control system.