This article was printed in CONTROL's August 2009 edition.
By Doug Rothenberg
The plant operator has an extremely valuable and important responsibility: managing the real-time performance of a capital enterprise easily worth hundreds of millions of dollars. We ask operators to shoulder the burden of everything that goes wrong during their watch, all without any recognition when nothing does, and precious little—and that mostly blame—when it goes wrong, and they manage to manage. Within their area of responsibility and authority, they must be able to view every control loop, most sensors, most pieces of equipment and most of the supporting utilities, and then adjust as appropriate.
The failure to maintain situational awareness has been present in almost every disaster event that was not the result of a spontaneous, complete surprise. No one wants an accident. But accidents and disasters happen. We now know to a high degree of certainty that they happen because those in charge of ensuring that they don't aren't aware of critical events as they are happening. They fail to know the situation. They are unaware of what is really going on, what is likely to happen, or what isn't happening that they think is. As pointed out in my forthcoming book, Alarm Management for Process Control, from Momentum Press, this situation can be significantly improved by good operator interface design.
Evolution of the Technology
The video display unit seemed to represent a significant step forward when it replaced panel boards. Actually, it was a step forward in technology and a step backward in operator support. But it was the evolution of displays, not their intrinsic faults or limitations, that led us down the wrong early paths. Once the faceplate barrier was broken, so to speak, the world of graphic design opened up. As soon as color made the scene, all of the process control system (PCS) manufacturers started a race to see who could use the most appealing and exciting colors to flash in front of prospective buyers. What was missing from all of this new technology was the the answer to the question of what the video display should do and how best to do it.
Physical Display Architecture
We know that more screens are as necessary as more information is displayed. Figure 1 shows a recommended architecture. There are enough screens so that most tasks, including monitoring, can be viewed at the same time without requiring switching displays on a screen, much like a panel wall. The locations are arranged so that related information is naturally located.
The screens that provide more global information are located above. As a package, the displays on these screens complement the operator's role of observing and managing. At top left, would be the screen dedicated to the alarm system. The screen at top center provides overview information on how well the process is working. This aids the operator working to ensure the plant doesn't go astray. The operator may also be working on process improvements. The screen that supports improvements is located at upper right.
New Operator Screen Design
What you see here depicts a best practice for graphical operator screens. It was developed based on the work of the authors listed in the sidebar, "More About HMI Best Practices." Note that color is used only for information—to point out the unusual or abnormal.
- Shaded grays are used to delineate the operator's arena of responsibility.
- Contextualized icons focus on what's normal and what's not.
- A hierarchy of view provides
a. Critical information only at overview,
b. Robust details and causality at the secondary view(s),
c. Support and guidance at the tertiary view(s).
Consequently, what the operator now gets is a powerful tool that focuses attention and encourages efficient navigation to what's he or she needs to see and attend to without the overhead of "clicking to oblivion" that we always find in conventional personal software.
It's All About the Bars
Coding Schemes and Icons
Icons are powerful codes meant to be in-your-face obvious. This is the stuff that speeds up understanding and minimizes confusion. Icons both evoke a meaning and confirm that what is evoked is correct. While it might seem to be redundant, such redundancy is important.
Now, let's put all these elements together. Illustrated in Figure 3 is a best-practice overview level display. Notice that all of the process elements are represented by neutral gray. This is what we expect. Process elements are placeholders. They're only there to show causal relationships and where things are okay or not. Arrangement conveys causality. Color is used for information only. Okay, there is the legacy video inset for the flare camera! It always needs to be in view.
Figure 3. A best practice for displays is to show all process elements in gray. Color is used for information only.Note the selection of key input variables at the left margin. These are "produced" by others at the enterprise. While not clearly depicted, the graphs of each input variable are contextualized in a manner similar to the icons. Their degree of normalcy significantly affects the production within our operator's area.
Next, we see the entire operator area of responsibility laid out with all key internal variables identified by context-bearing icons. Anything wrong will easily show up. Finally, observe the key product variables at the right margin. If these are okay and the process is okay, there should be confidence that the enterprise is okay. Where things are not, they show up directly and clearly.
More about HMI Best Practices
Corbett, D. Legg. Man Machine Interface. Litwin Process Automation, Houston, Texas, 1990.
"Effective Operator Display Guidelines," ASM Consortium, http://www.asmdashboard.com/, 2002.
Hollifield, B., D. Oliver, I. Nimmo and E. Habibi. The High Performance HMI Handbook. PAS. http://www.pas.com/. Houston Tex., 2008
"Human Machine Interface." NAMUR Standard AK 2.9. www.namur.de/ Potsdam, Germany.
"Process Plant Control Desks Utilising Human-Computer Interfaces–A Guide to Design, Operational and Human Interface Issues." Engineering Equipment Materials Users' Association (EEMUA) Publication 201. www.eemua.co.uk/ London, 2002.
Do ASM-Style Displays Work?
Sound like good ideas? Luckily, tragic incidents happen rarely, so very few plants that have employed the new designs have had one. With the new design, they are even less likely to see one at all. So we don't have actual case histories to demonstrate this. As a surrogate, carefully designed simulations were prepared and experienced operators used to work them. (See Errington, Jamie and Peter Bullemer, "Advanced Operator Interface," Human Centered Solutions, http://applyhcs.com/: 2008.)
The overall statistics from this test are very encouraging. In general, those using the ASM type displays were twice as fast in managing and almost 40% again more accurate. Even more revealing, those using the ASM displays were four times faster at early event detection.
By combining good human-factors engineering and years of experience with graphic displays, we've made significant strides forward from the big steps backward we made when we abandoned the panel wall. The plant operator gets the tools needed to do the job.
Dr. Rothenberg is principal of D-Roth Inc., www.d-roth.com, a subject matter expert in alarm management and operator interface development.