The Great Graphics Debate: Is Going Gray Good for HMIs?

Nov. 18, 2016
Just when you think industry has settled on a look for HMI graphics, things change. But HMIs are not video games, and colorful, action-packed screens are not necessarily the best way to support safety and enhance productivity.

This is the advice that Larry Sawicki gives for specifying graphics for industrial human-machine interfaces (HMIs). The control systems engineer at Pima County Regional Wastewater Reclamation Department in Arizona urges automation professionals to adopt a graphical-design strategy that focuses the operators’ attention on the things that require it.

He and his colleagues are among a growing group of automation professionals who have learned firsthand that good graphics are really about effectiveness, not attractiveness. These professionals are eschewing the color-intensive, action-packed graphics that have become increasingly available on industrial HMIs. They are instead going for designs that take into account human factors and the principles of situational awareness to keep safety and productivity high.

The result has been the emergence of a simpler, grayer, almost minimalistic look designed to draw the attention of operators and technicians to situations that require their intervention. Such designs typically depict backgrounds and items running normally in shades of gray and reserve color and motion for highlighting abnormalities.

Because the goal is to draw attention only to those situations that require action, this design philosophy uses color, shapes and motion sparingly so they will stand out against the background when needed. “Color can be very effective in catching the attention of an operator, but overuse greatly diminishes its ability to capture the operator’s attention,” notes John Krajewski, director of HMI and SCADA product management at Schneider Electric Software. “When it’s important to keep the operator focused on the most important task or situation, a limited use of color is most effective.”

This design philosophy played an important role in the upgrade undertaken by Pima County to improve phosphorus and nitrogen removal at its Tres Rios Water Reclamation Facility in Tucson, Ariz. Because success depended upon the operators’ ability to manage the automation in the facility, the upgrade included the HMIs on its Wonderware supervisory control and data acquisition (SCADA) system from Schneider Electric. The old design had been overwhelming the operators with too much data and too many nuisance alarms.

To avoid overwhelming operators at the Tres Rios Water Reclamation Facility with too much data, the graphical presentation of control data on the upgraded HMI/SCADA system is based on situational awareness principles, including simplicity and a limited use of color. Source: Schneider Electric Software

Using Wonderware InTouch software, Pima County’s engineering staff was able to avoid this problem by applying the principles of situational awareness. The window structure, color scheme and alarm hierarchy of the HMIs not only present information about the processes and systems in the context of their operating environment, but also highlight abnormal activity. This enhances the staff’s ability to perceive and understand what is happening in the water reclamation facility and focuses its attention on what needs to be done.

As a consequence, key alarms no longer get lumped in with the nuisance alarms. Operators now address them right away before they have time to fester and develop into serious problems.

Minimalism vs. realism
The approach taken by Sawicki and his colleagues at Pima County stands in stark contrast to a concurrent trend among other automation users. This second group of users is embracing high-intensity graphics and putting them on their HMIs. Often, their intention is to add a touch of realism to the piping and instrumentation diagrams (P&IDs) and other graphical representations in control rooms.

Realism also allows machinery builders to encode some help for operators inside the HMIs. As the cost of system memory continues to fall, more HMI manufacturers are exploiting the economics to offer features such as video clip storage and playback. “Machine builders are quick to pick up on this feature to embed things like operator instruction or machine fault diagnostic videos,” says Clark Kromenaker, product marketing manager for HMIs at Omron Industrial Automation.

A touch of realism on faceplates, for example, can also enhance the safety of interacting with a machine. “The operator can adjust the HMI-displayed template of an array of smart sensors, just as if he had the control cabinet door open and was making adjustments to the physical device itself,” Kromenaker explains. “So such a faceplate enables a more realistic virtual involvement with parts of the machine without some of the hazards that might be present if the control cabinet door was actually opened.” Such faceplates also exist for recipes and alarms.

The problem with realism, however, is that it is easy to overuse. “Furnaces with dancing flames and detailed floors and walls are colorful and fun to look at—and may sometimes sell HMIs—but they don’t necessarily provide useful control information,” says Matt Newton, director of technical marketing atOpto 22. “In fact, they often serve only to distract the operator on the job.”

He and others point to studies that link inappropriate HMI design to operator error and low productivity. Investigative bodies—the U.S. Chemical Safety and Hazard Investigation Board, for example—have identified HMIs as causal factors in the Texaco Pembroke, Esso Longford and BP Texas City explosions. And a study commissioned by the U.S. Navy found that users of simple, abstract graphics outperformed users of video game-style graphics by 70 percent—despite an overwhelming preference among the users for the video game look.

Tone down the color
As one might suspect, such findings have sent industry on a search for design principles that would enhance operator performance and plant safety. Some of these earliest studies were conducted by the National Aeronautics and Space Administration (NASA) and packaged for the process industry by the Abnormal Situation Management (ASM) Consortium, according to Ian Nimmo, who was the consortium’s program director at the time.

He believes that NASA’s research into perceptual layers has been the most important advancement in HMI design. “It provides rules for color use, text size and line width for readability and clarity,” says Nimmo, who is currently president of consulting firm User Centered Design Services (UCDS). This research found gray to be the best background color and 3:1 to be the minimum recommended luminance contrast ratio between symbols on the screen and the background.

Since this early research was done, other industry-sponsored consortia and universities have been conducting their own research. The Center for Operator Performance (COP), for example, has been studying how research into human behavior and situational awareness can mesh with new graphical technologies to enhance operator performance. COP’s work has contributed to the evidence that relying on a lot of color has several liabilities—liabilities that go beyond being distracting.

One example is the color codes that HMI developers will often deploy in their designs to denote such things as stoppages (red), systems that are running (green) and suboptimal conditions (yellow). Not only do people interpret colors differently, but they also have limits for doing so. “Human beings can detect only about seven colors on an absolute, rather than a relative, basis,” explains Thomas Kindervater, COP’s solution support manager. To be effective in any coding scheme, therefore, colors must be few in number, and each must have only one meaning associated with it.

“We also learned that, for a coding system to work, it has to be simple and intuitive,” Nimmo adds. “If there was a coding system on HMI graphics that used multiple colors, it was lost after the first five minutes.”

This is not to say that HMI developers should avoid colors. Using some color is good design practice—but the guiding principle should be that color should deliver useful information to the operator quickly, efficiently and even intuitively. Consider a graphic that turns red when a certain parameter reaches a threshold value. “The operator should be able to see the light and not have to ask, ‘Why is that light on?’” Opto 22’s Newton says. “The HMI must clearly inform the operator that this is a problem.”

Beware: Motion captures the eye
Color is not the only way to capture an operator’s attention and convey information. “Shape, size, blurring, movement, line width, line placement, line size are all tools for coding systems,” Nimmo says.

The same general rules about using color sparingly also apply to these other techniques, especially to motion. “People’s eyes are naturally drawn to motion,” Newton explains. “If an HMI includes use of a video or a moving graphic, its movement had better show the most important thing on the screen, because it will draw the operator’s attention away from everything else.”

Kindervater advises, “When the process is operating within expected limits, the displays should be devoid of any intense colors and have no animated objects.”

Although the trend toward minimalism might seem to be a rejection of the latest in graphics technology, this is not necessarily the case. In fact, sometimes, advanced graphics are actually responsible for making minimalism possible. A good example is the advanced shapes described by Andrew Stuart, Experion HMI product marketing manager at Honeywell Process Solutions. These shapes replace complex objects with simple graphical representations that convey process-control information intuitively without numbers.

One of these shapes might represent a level indicator on a holding tank as a vertical bar whose length corresponds to the measurement range of the actual gage. On such a shape, a horizontal line might move up and down the bar to report the current measurement, and a small, horizontal arrow might sit at the set point. The vertical bar would probably also have some shading to indicate the in-control operating range that would not set off any alarms.

“The operator can learn the status of the process just by looking at the shape,” Stuart notes. “All of the control information is contained in a very compact, small shape, so the operator knows at a glance what he should be controlling to without having to interpret any numerics. If the process variable and the set point are the same, the process is in control.” If they are not the same, the operator can see how close the variable is to its control limits.

This capability is both possible and practical because of the reasonable cost of high-resolution monitors today. Older screens simply did not have enough resolution to show these kinds of slight movements or to provide the shading for denoting the control limits. Now that the resolution is available, “we have seen a slow progression to supplementing P&ID displays with advanced shapes,” Stuart reports.

The debate continues

Aiming for clarity in HMI, automation vendors like ABB are recommending cool, gray graphics to depict processes running normally. By reserving color for abnormal conditions, developing problems are more likely to stand out and draw an operator’s attention before getting out of hand. Source: ABB

As technology continues to advance, it will continue to influence the look of HMIs. In fact, advances in graphics engines and object-oriented engineering are behind the whole minimalist movement. “The concept of situation awareness and ‘cool’ or gray-scale graphics aren’t new,” notes Roy Tanner, global product marketing manager for control technologies at ABB. “In the ’90s, they weren’t available on HMIs for distributed control systems. Black was the background of choice because there was no other option.”

Consumer applications of graphics technology will continue to lead industrial applications and be a testing ground for industry. HMI developers are already trying to build on the experience that people have with their tablets and smartphones at home. “Beyond generating a comfort level among users, this goes a long way to perfect the user experience and shorten the learning curve for machine operators,” observes Eric Reiner, industrial PC market specialist at Beckhoff Automation.

Not only does use of consumer devices train people in using technology, but the consumer industries have been developing technologies to make sophisticated devices intuitive to use. “Features such as multitouch, so users can pinch to zoom and use swiping gestures, help to increase the efficiency of even the most non-technical of users,” Reiner notes. Hence, they reduce the need for training operators and other technicians when they find their way into industrial machinery.

Because people get used to technology, not everyone is convinced that the current science behind minimalistic use of high-intensity graphics is final. “Ten years ago, I would have said there is no place for video game-like graphics,” Tanner says. “I may have to revise my thoughts on this, though, as digital natives come into the picture and replace the retiring workforce.”

He wants to see what research into human factors reveals about the abilities of those digital natives once they are old enough to enter the workforce. “The level of information that is organized and presented in video games is amazing,” he says. Will children who grow up using these methods learn to extract the necessary information from such graphics accurately enough in real emergencies? Only time will tell.

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