Distributed control systems are powerful assets for new and modernized power plants. Thanks to three product generations of technology innovations, these systems now provide new benefits — including improved O&M efficiency, greater plant design flexibility, and improved process control and asset reliability — that help competitive plants advance in the game.
With nearly 30 years of evolution — and three fundamental technology generations — since their initial introduction into power plant applications, distributed control systems (DCS) have improved considerably. Though specific release dates vary among vendors, the first generation of DCS appeared during the 1980s, the second generation during the 1990s, and third generation in the mid-2000s.
With each major system release, many new DCS capabilities and features have been added, resulting in new benefits for plant designers and owners.
First Generation: The Early DCS
The introduction of microprocessor-based plant control occurred shortly before 1980 with simple single-loop controllers. This technology quickly evolved into a DCS with control processor redundancy, high-density input/output (I/O) systems, and a human machine interface (HMI).
Perhaps the most significant feature of the early DCS was the ability to geographically distribute control system processors and I/O components, thus influencing power plant designs by greatly reducing the amount of field wiring needed between control equipment and field instruments.
As the first-generation DCS evolved, advances in technology enabled PC-based engineering tools as well as function block programming, which greatly simplified the construction and flexibility of controller-based application code. As controller speed and memory increased, control system engineers quickly realized that control logic strategies truly would only be limited by the engineers’ imagination.
When compared to previous technologies — plant computers and electrical analog control systems — the first-generation DCS stands out as a tremendous leap in technology for its time.
Second Generation: The Open System DCS
One limiting factor of first-generation systems is that they were designed to use proprietary communication technologies. Consequently, connections to third-party systems were typically limited to custom-developed interfaces. This changed during the 1990s, and the DCS became recognized as the optimal vehicle for integrating process data from the various automation platforms used within a typical plant.
The open system DCS provided standard communication interfaces for connecting the various automation subsystems. Supporting integrated plant operations for all automated plant equipment, the DCS provided a centralized and common "single window view" of plant data for control, logical interlock, alarm, and history. Enterprise management solutions, also enabled by the open system, provided new opportunities for fleet management centers to improve operations by remotely monitoring plant processes, analyzing unit efficiencies, and supporting coordination between operating units.
Additionally, the use of commercial off-the-shelf technology emerged during this period as standard Ethernet networking components and Microsoft Windows-based systems were applied at the DCS HMI layer.
As demand for more open systems grew — along with strong interest in integrating fieldbus technology and making full use of an integrated operations and engineering environment — the third-generation DCS emerged.
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