Who wants to be responsible for designing an HMI graphic that can lead to confusion, cause eye fatigue and cause operators to make serious mistakes? That's the key question posed in an HMI graphics design presentation at Rockwell Automation's RSTechED event in Orlando, Florida, last month.
Dave Board, a Rockwell commercial manager, shared his best practices on how to design effective HMI screens for plant operators, noting that good situation awareness for operators "means being aware of what is happening around you, understanding what the information means to you now, and understanding what that information means to you in the future. It also relates to the goals and objectives of a specific job or function."
Board said designers and engineers form a different mental model of the process in their heads than operators. "By understanding how operators select and use goals, designers better understand how information is perceived," he said. "Without understanding the user’s goals on situation awareness, the information has no meaning."
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Contrary to the wonderful, imaginative, animated, 3D color graphics available to designers today, Board makes it clear that they have no place in a best practices list for industrial operator displays.
"Use gray background, vessels and pipes in low-contrast grey," he said. "High-contrast color objects strain the eyes and cause fatigue. Warm colors, especially when flashing, draw the operators attention to them. Color should be used for abnormal conditions only." There should be little or no movement of objects that cause unnecessary distractions.
Board also is a big fan of analog status indicators. "The brain interprets analog more quickly than a number," he said. "We should provide a pointer to a scale, provide a clear indication of the normal working range, and clearly show upper and lower limits."
With an analog display, the operator easily can see where the value is, as well as what it is. And he can see rates of change easily.
Board says low-level details of the plant should be accessed by clicking to them when needed. And the navigation should be as consistent as possible across displays.
Board gave high praise to several references as the basis of his presentation, and strongly recommended that session attendees read them. They are:
- The High Performance HMI Handbook, PAS, Bill Hollifield, Dana Oliver, Ian Nimmo and Eddie Habibi
- Designing for Situation Awareness, Mica R. Endsley and Debra G. Jones
- Human Machine Interface Design: The Good, The Bad and The Ugly, ICS Triplex, Paul Gruhn, PE