Distributed Control

How the DCS Has Spread Its Tentacles into Every Aspect of Factory Control

For 25 Years, We've Watched in Wonder the Progress of Our Most Powerful Systems

By Paul Studebaker

In 2015, the distributed control system (DCS) will mark its 40th anniversary—40 years since the first Honeywell TDC-2000 beta-types were installed at Exxon's Sarnia, Ontario, refinery, and Yokogawa introduced its version, CENTUM. By 1980, Bailey (now part of ABB) introduced the NETWORK 90 system, Fisher Controls (now part of Emerson) introduced the PROVoX system, and Fischer & Porter (now also part of ABB) introduced DCI-4000.

During this period, the DCS swept alternative process control technologies from the field. "In the late 1970s, market analysts projected the decline of analog control, but no one anticipated the speed or completeness of this transformation," wrote Terry McMahon in April, 2005. "At least two generations of process control engineers have matured during the DCS era, which has endured much longer than earlier technologies."

Honeywell had been working on a dedicated digital loop controller since 1969, but the problems of reliability and cost seemed insurmountable. The emergence of the integrated-circuit microprocessor in the early 1970s solved these problems. The Intel 8080, announced in early 1974, was the breakthrough event enabling multiple control loops to be handled with a single microprocessor.

At the time, "Foxboro's analog controllers were generally considered the class of the industry," McMahon wrote. "The SPEC 200, announced in 1972, was the high-water mark of analog electronic technology, and ISA's 4-20 mA standard [SP50] was approved in 1975 just as this technology was being rendered obsolete by digital controllers."

See Also: Let the DCS Fit the Process

In the 1980s, users began to look at DCSs as more than basic process control. If proprietary systems were opened, data could be shared and greater things could be achieved. This led to adoption of UNIX operating systems and Ethernet-based networks. The full TCP/IP standard was not implemented, but using Ethernet allowed object management and global data access.

PLCs were integrated into the DCS infrastructure, and plant-wide historians emerged to capitalize on the extended reach of automation systems. The first DCS to adopt UNIX and Ethernet networking technologies was Foxboro's I/A Series.

The 1990s saw increased adoption of commercial off-the-shelf (COTS) components and IT standards, and the controversial move from UNIX to Windows. Even today, the real-time operating system (RTOS) for control generally remains on variants of UNIX or proprietary operating systems, but above that, applications tend to be based on Microsoft systems.

As the DCS became increasingly network-centric, many suppliers built new "process automation systems" from the ground up to maximize functionality with Ethernet and fieldbuses. These include Rockwell Automation's PlantPAx, Honeywell's Experion, ABB's System 800xA, Emerson's DeltaV and Siemens' Simatic PCS 7.

Since the inaugural issue of Control magazine in October, 1988, we've made the DCS the center of our process control coverage. Over the past 25 years, we've described how DCS has evolved from distributed control with centralized microprocessing, to "truly distributed control" with centralized supervision of microprocessors in the field, to today's rise of virtualization, where critical and non-critical functions coexist in servers (or even the cloud). Control, safety, supervisory, historian and business functions are increasingly distributed as needed in network-based architectures across field devices, controllers, thin clients, central processors and the Web.

With increasingly inexpensive and standard COTS hardware and operating systems, the heart of the DCS is moving from equipment to software and services. Applications now include production management, model-based control, real-time optimization, plant asset management (PAM), real-time performance management (RPM), alarm management and more. Indeed, much of today's most exciting activity is in wireless networks, mobility, remote access, business optimization and real-time decision-making, which largely run on hardware that's independent of the DCS.

The words we used in 2013 to describe the latest permutation of the original DCS, Honeywell's TDC 2000, sum up the best of today's systems: "You'd think a DCS as useful and successful as Experion PKS Orion R2 might stop for a well-deserved break, or at least pause to catch its breath and allow its many fans to catch theirs," wrote Jim Montague. "But that's just not how its developers operate. Together, they just keep churning out an unrelenting stream of improvements, capabilities and innovations, until it seems like there's nothing that Experion can't do—and maybe that's the point."

Timeline: 25 Years of DIstributed Control Sytems History