The past decade has seen an explosion of technology that has significantly altered the process control industry. The adoption of commercially available technology driven by desktop computing has allowed suppliers to focus on applications to enhance the process and deliver ever-greater value to the user.
Ten years ago at the 1998 ISA Power Industry Division symposium, several papers were presented that reviewed then-state-of-the-art developments in distributed control systems (DCS) technology. Those developments included the emerging trend to incorporate greater amounts of commercial off-the-shelf (COTS) technology into what had traditionally been highly proprietary, vendor-specific architectures. Specifically, those COTS components found in the desktop computing industry included personal computers (PCs) for DCS controllers and workstations, as well as commercially available networking technology such as Ethernet and fiber distributed data interface (FDDI).
New Designs Emerge
Although the DCS platform is sure to continue evolving to track the desktop computing industry, the significant developments will be in the ability to apply more-sophisticated applications that take advantage of the ever-increasing speed, power, and flexibility those platforms will provide.
We also have seen the emergence of control system technology that widely incorporates elements of conventional desktop computing technology. From operator workstations to process controllers, networks, and various operating system elements, the process control industry has embraced standard desktop computing and adapted its technologies to the unique needs of industrial control applications. DCS technologies will continue to expand in capability through the incorporation of "open system" technologies.
The first move in this trend began in the early 1990s with the gradual incorporation of UNIX workstations and, to a lesser degree, PCs for human-machine interface (HMI) functions. Though some were initially leery of applying these COTS technologies in mission-critical control applications, the apps gradually gained acceptance (Figure 1).
1. Pushing the limits. The processor speeds of human-machine interfaces have increased by a factor of 425, and memory has increased by more than a factor of 1,000, over the past 20 years. Source: Emerson Power & Water Solutions
Through the 1990s, as computing power, speed, and reliability in both UNIX and PC technology increased at geometric rates, users increasingly embraced COTS desktop devices for HMI functions instead of proprietary vendor-specific HMIs. Whereas a decade ago the UNIX workstation was the most common choice, primarily due to the perception that it had a more robust operating system, today the vast majority of users are opting for the more familiar Windows PC for HMI applications.
Also in the 1990s, the rapid growth in desktop computers’ microprocessor power and speed led to the next logical evolution in control technology. Control system suppliers adopted these developments and moved away from highly proprietary "unique" controllers and architectures. They began incorporating controllers utilizing PC architecture, albeit an architecture adapted to the redundancy, fail-safe operation, and environmental hardness demands of industrial control applications.
Although they are not strictly using COTS boards for controllers, DCS providers do use standard commercially available components and architectures — but on custom-designed boards to meet the demands of the industrial control environment. Since they were first introduced in the late 1990s, these "PC-based" controllers have been able to seamlessly track the more than tenfold increase in processor speed, offering system designers and users significantly more options than in the past.
The DCS network, or data highway, is the third area where commercially available technology has forever changed the process control industry. A decade ago, DCS data highways were highly proprietary architectures designed to facilitate communications only between DCS components from one specific vendor. There were no standard architectures; some highways were completely vendor-designed, while others were loosely based on standards, but those standards were unique to their particular system. Communications outside the highway were difficult and required custom data links to be developed, often at great expense.
Again from the desktop computer industry, two de facto communications standards arose: FDDI and Fast Ethernet. Both operated at 100 Mbps — 10 to 50 times faster than the proprietary DCS networks of the day. And though neither offered the deterministic features that most DCS networks provided, their speed and overall high level of reliability made them more than adequate for industrial control applications (Figure 2). They also had the benefit of more easily opening the system and making interconnection with third-party devices and corporate information networks far more practical than with a proprietary DCS network architecture. Over the past decade, the Fast Ethernet architecture has gained market dominance and has been joined by an even larger, Gigabit Ethernet standard that has great applicability in multiple network DCS architectures.
2. Much-improved performance. The processing speed of logic controllers has increased by a factor of 50 since 1988. Source: Emerson Power & Water Solutions
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