What Is the High-Performance HMI?

Operators Learn to Live With Design Flaws and Often Take the Easy Way Out and Live With the Less-Than-Perfect Systems They Grew Up With

By Ian Nimmo

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Many operators complain of eye-strain because of high-contrast color usage and the use of  >3:1 contrast ratio for colors, such as extremes of brightness from yellow-on-black backgrounds.

Why Users Like the current System

The eye has to adjust to light and dark continuously, especially with the extremes of light and dark in the environment. Most control rooms with these style graphics are kept dark to reduce glare issues. However, windows, task lights, ceiling lights and windows all create problems in these types of environments.

Graphics designed in this way suffer from poor or lacking functionality. They create an environment that supports human error. For example, they exacerbate short-term memory issues. These can inclulde operators forgetting they've made a manual move, such as opening a drain valve or bypassing an alarm. This system also generally creates high levels of cognitive workload as operators try to diagnose problems by searching for information, all the while keeping an eye on the operation. In the past, we have experienced many data entry problems, which often happen when the operator is several moves ahead of display updates.

The bigger issue with human error is one I've described as situation awareness issues. These touch on some of other areas, such as salience or misplaced salience, data overload and attention tunneling. Each of these deserve a white paper of its own. Other issues include distractions, communication breakdowns, out-of-loop syndrome, complexity creep, workload, fatigue, and working with the wrong mental model due to use of P&ID style.

Some quick fixes are available, and include reviewing  existing graphics against a formal philosophy and style guide, addressing issues around consistency, and only making graphics pop for important information. You can improve readability by addressing text font and character size or height, and by controlling color and following strict coding rules. Apply similar rules for lines and graphic objects. Address visual clutter, and follow rules regarding how much white space should be left and how many screens each operator should be following. Develop of a hierarchy of graphics views—overview, unit view, detail view and diagnostic view—instead of just using a flat P&ID view. P&IDs normally live down at the detail view. Also, training, management of change and documentation practices often need to be added to a graphic enhancement project.

Weaknesses of the Current System

All or Nothing?

Some of the biggest questions I'm often asked are, "Is it all or nothing? Can we do anything to our existing graphics without throwing away what we have? Or, do we have to redesign them totally?" Those are great questions.

I view improvement as an iterative process. Often it all depends on what else is happening. If you're going through an automation replacement, it makes sense to redesign the graphics to today's new standards. Many parts of a current design—the good parts—can be kept, but chances are the new techniques will require something that does not exist in the present design. Many of our customers testify that the new design techniques often result in a significant reduction in the number of graphics or schematics.

The important thing is to have a roadmap, in the form of a philosophy and style guide, which will ensure that the designer and users understand the rules for designing and building graphics, and address the issues of consistency, clarity, variability, etc.

In additon, the greatest lesson that designers and users need to understand about BPCS graphics is that they need to be layered. The background layer should be for fixed reference information, the next layer for variable information, then notifications, then alarms, and finally safety-critical alarms.

The pop-outs at the very front are controlled by color, thickness, brightness, contrast, etc. This allows different priorities to catch the operator's attention, provides improved situational awareness, and allows the graphic to work with the alarm system, rather than being a competitor for the operator's attention.

Finally, new graphics should be designed to the new life-cycle model promoted by ISA-101 draft standard, and follow Human Factor/Ergonomic rules outlined in the ISO 11064-5 standard. 

[Editor's mote: In the October 2012 issue, Ian Nimmo will focus on taking advantages of the opportunities offered by following best practices in HMI design.]

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