Does DCS Have a Future?

Figure 1. A “typical” DCS system, depending on whom you ask.
Image courtesy of Siemens E & A.

The days of proprietary control systems are over—almost. According to Peter Martin, vice president for strategic ventures at Invensys Process Systems (IPS), the trend toward commerical off-the-shelf (COTS) systems began in 1987 when Foxboro introduced the I/A Series control system and with it the concept of using standard hardware, software and communications in a control system. (For a discussion of “Should Control Engineers Do Windows?” scroll to the bottom of page 3 or use the following link www.controlglobal.com/0812DCS.html.)

Todd Stauffer, PCS 7 Marketing Manager at Siemens Energy & Automation, says, “In 1998, the DCS was coming out of the proprietary age. The move toward open systems and commercial off-the-shelf technology was driven by users and suppliers alike. This transition has allowed the pace of technology innovation to increase. We would have never made it to this point if we had stayed proprietary.”

Proprietary networks have been replaced with various versions of Ethernet and COTS routers, switches and wireless devices. Computer hardware is all standard stuff, all based around the same basic hardware and Windows-based software. In fact, some DCSs use conventional controllers and HMI/SCADA software, says Jim Ford, director at system integrator Maverick Technologies. “DCSs are thrown together all the time with PLCs for basic control and software, such as Wonderware used for the HMI.”

Thanks to their conformity with fieldbus, HART and other industry standards, most process sensors and transmitters have nothing proprietary about them. You can use anybody’s hardware in your control system.

The major DCS vendors also use fieldbus because they have the necessary hardware and software. While fieldbus is not proprietary, only the big DCS vendors have made the necessary investment in things like fieldbus protocol stacks and H1 cards. Few, if any, of the competing HMI/SCADA control systems offer fieldbus, but this will change as soon as fieldbus hardware becomes available for PC-based systems.

So what’s still proprietary? The hardware controllers and I/O from most major DCS. vendors.

And software, of course. Or is it? Some DCSs use historians, asset management programs, loop-tuning programs and ERP software from the same suppliers—as do several of the HMI/SCADA-based control systems, such as Wonderware, Citect, Indusoft and Iconics. Both the big DCS and the HMI/SCADA-based system vendors claim to have completely integrated software from the loop controllers to ERP.

From an architecture standpoint, the major difference between the two is that DCS systems use proprietary hardware, while HMI/SCADA systems use conventional hardware, such as PLCs, panel PCs and hybrid controllers.

HMI/SCADA: A Viable Competitor of DCS

From a functionality viewpoint, an HMI/SCADA system can offer exactly the same capabilities as a DCS (except for fieldbus). An HMI/SCADA system uses the same field devices, the same Ethernet networks and the same COTS-based HMIs as a DCS. An HMI/SCADA system has the same type of software available as a DCS.

To counter claims that HMI/SCADA can’t handle “big jobs,” Scott Kortier, marketing communications manager at InduSoft, points to Brookhaven National Labs, in Brookhaven, N.Y., with its Relativistic Heavy Ion Collider (RHIC). Indusoft recently upgraded the RHIC’s control system. “This system includes over 10,000 I/O points, a dozen operator stations plus 15 security-enabled, browser-based displays,” says Kortier.

Tim Van Wyk, a development engineer with Citect, agrees. “SCADA can provide the offerings that have been perceived to only come from a DCS solution,” he says. “With an open SCADA system, customers can use partners that bring the best industry experience and advanced technologies to their SCADA solution without relying solely on a single source, as with a DCS. When customers need to quickly adapt to changes in their business environment, an open SCADA provides the flexibility, which can be difficult and slower with a closed DCS system.”

Naturally, DCS vendors disagree. Randy Reiss, a DeltaV developer at Emerson Process Management, says, “There are inherent limits to the throughput of the communication of SCADA level products. The vendors of SCADA-level products are subject to the operation of technology below them to send and receive data, resulting in a less-coordinated communication subsystem. A major benefit of a DCS is that the system is all developed together. What is usually the truth is that there are a bunch of little systems that have minimal communication between them. That means that an operator cannot call up a display from outside the immediate area or trend data across the plant to look for correlations. Try and get end-product quality side by side with raw material data…good luck!”

Citect’s Van Wyk counters, “There is no separation of data across little systems. Users can leverage data from components onwards to the open MES product expanding the total solution to the business enterprise.”

DCS vs SCADA

The “classical controls vendors” who produce DCSs bring extensive industry experience, an army of engineers and a completely integrated hardware and software solution to the table. They are formidable competitors to HMI/SCADA systems, and they are at the cutting edge of control.

“It’s the DSCs that are at the forefront of technology and are the future of control,” says Randy Reiss. “It’s the DSCs that are blazing the trail and designing the systems that enable advanced technologies like multivariate statistical process monitoring, MPC and wireless. It’s all in a DCS before it’s in a SCADA product. So if you want to see the future of control, look at the big DCS venders. They are the ones throwing things on the wall to see what sticks.”

That knife cuts both ways, says Van Wyk. “With open SCADA systems running on Windows, users get to leverage not only their industry-specific software, but also access worldwide software developments. When running a DCS, users have to wait for software to be redeveloped within the closed DCS software environment.”

DCSs also can do top-to-bottom integration for both hardware and software. Harsh Chitale, vice president, strategy and global marketing at Honeywell Process Solutions, says a DCS,  “…marries information management with knowledge-based technologies, including optimization, model-based control, simulation, abnormal situation management, scheduling, wireless and advanced sensing, and advanced applications, and delivers that them in a form suited to industrial manufacturers.”

Roy Tanner, Systems Marketing Manager at ABB, says, “DCS advantages include pre-integrating/testing various components and having single stores of data and information. This has expanded beyond traditional HMI and control to other functional areas such as safety-instrumented systems, electrical system integration and asset optimization. Also, DCS systems are released as a pre-tested, pre-integrated ‘system’ which reduces complexity by NOT having multiple database synchronization, backup and disaster recovery issues, various software revision levels, and multi-vendor support issues.”

“There will always be a need for the more tightly integrated system that a traditional DCS provides,” says Dave Emerson, Director of Yokogawa’s U.S. Development Center, adding “This scalable level of integration provides the benefits of an integrated DCS and the connectivity of traditional SCADA designs.”

On the other hand, HMI/SCADA suppliers typically rely on a network of systems integrators to install and configure their control systems. This is not a bad thing, because many systems integrators are just as qualified as the DCS vendors’ engineers. However, SIs are often constrained by their customers’ preferences toward certain vendors.
Ed Diehl, executive director of Concept Systems, says, “We work with our customers to identify the best architecture for their application and circumstance. In virtually every case, there are numerous control technologies that will do the job. The key is to find the best one for that customer and to integrate it properly.”

But in the end, “A key ingredient to the concept of DCS is homogeneity,” says Dennis Kilgore, president of DLL Solutions. ”This comes somewhat from the need to have a ‘single neck to choke,’ instead of vendors pointing fingers in order to escape blame.”

And therein may lie the primary reason for the continued success of DCSs, in spite of their high cost—three times that of a comparable HMI/SCADA system, by one estimate. A DCS vendor can supply a completely integrated system—all from a single vendor who takes responsibility for the delivery, configuration, startup and maintenance.

What’s Next?  

So what’s in store for future distributed control technology? Clearly, the march to open systems continues. There are no significant hardware differences between the proprietary controllers of DCS vendors and the PLCs/PACs of the HMI/SCADA systems. So it is safe to predict that a universal open controller platform will emerge. 

Mark Nixon, chief architect of DeltaV at Emerson Process, says one of the catch phrases these days is smart plants. “These smart plants operate to tighter specifications, involve a much greater understanding of the processes, greater automation and decision support, more expansive use of automation and data interpretation. ”

ABB’s Roy Tanner says control is moving to the field. “Due to technology and the adoption of standards, one of the trends we’ve seen is the distribution of control elements further into field devices,” he says. “If technology continues, unified fieldbus architectures with even more intelligent devices will change the role of the today’s process controller to that of a process ‘coordinator.’”

Peter Martin of Invensys calls this new breed of control system an enterprise control system (ECS) instead of a DCS. He says an ECS could include a conventional DCS, SCADA or other control technology, but it must also involve an architecture which enables full plant floor interoperation; open communication access across the enterprise; support for asset performance management tools that enable unfied maintenance and operations management; and a unified engineering environment across all plant floor domains.

“But there are forces in play that could affect the evolution of the DCS,” Stauffer warns. “Cybersecurity issues are responsible for ongoing changes in control system architecture and are making people think twice about implementing wireless. In addition, experienced process control engineers, operators and maintenance people are leaving the workforce. The next generation of DCS will have to compensate for this loss of knowledge, so it will be much more of a knowledge-based system.”

In the future, we will continue to see DCSes and HMI/SCADA solutions coming closer together until you can’t see the difference in technology. At that point, the purchase decision will come down to this: Who do you trust? 

Rich Merritt is a contributing editor at Control.