For certain industries, a distributed control system (DCS) provides substantially more value as the basis for automating the plant than a programmable logic controller (PLC)-based system. The DCS architecture has always been focused on distributing control on a network so that operators can monitor and interact with the entire scope of the plant. As such, the classic DCS originated from an overall system approach. Coordination, synchronization and integrity of process data over a high-performance and deterministic network are at the core of the DCS architecture. PLC architectures have always focused on very flexible and fast local control. Recent advancements in PLC technology have added process control features. When PLCs and HMI software packages are integrated, the result looks a lot like a DCS. But, all is not as it seems. This is very much a “do-it-yourself” (DIY) approach with plenty of technical risk as well as added costs that are not always immediately obvious.
HONEYWELL (2011) The Perils of a DIY Distributed Control System