The Trouble with HMIs (and How to Fix Them)

Rethinking HMI Design Leads to Better Operator Performance

By Nancy Bartels

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Problems abound in most human-machine interface (HMIs) designs in use today, many of which are the result of powerful software that made it perhaps too easy to create overly complex graphics that don't connect with the operator as effectively as they might.

John Krajewski, director of product management, HMI/supervisory, for Invensys' Wonderware brand, began his presentation on how to improve operator situational awareness by outlining more of the problems typical of today's HMIs: alarm strategies that are poorly defined and managed; screens based on piping and instrumentation diagrams (P&IDs) that don't support troubleshooting of upset conditions; screens that convey little awareness of how well the process is running and little warning if the process happens to be drifting toward a disruptive alarm.

Increasingly complex HMI screens are confusing, uninformative and contribute to human error. And human error in turn is responsible for 35% to 58% of process disturbances—those events that cause plant operations to deviate from their normal operational state, wasting energy and raw materials in the process.

What we need to do, said Krajewski, is clear away the clutter on our operator screens and instead design them for real situational awareness. He sees situational awareness as a pyramid. Perception of data or information is at the bottom of the pyramid. (The pressure is 85-psig.) Next up is comprehension of the meaning of the data. (But it normally is 72-psig.) At the top of the pyramid is an understanding of the implications of the information. (If I don't do something soon, the high pressure alarm will go off.) And a well-designed set of HMI screens helps build that pyramid of awareness for operators.

A well-designed set of screens contains the following elements, Krajewski explained:

  • It is goal-oriented.
  • It uses a hierarchical information organization.
  • It uses color properly.
  • It creates actionable alarm awareness.
  • It uses effective design elements.

Goal-oriented design is simply being clear about what it is you're trying to accomplish, said Krajewski. "A common mistake in HMI design is in thinking that the system itself is the goal," he said. "Keeping the system running is not the goal. The goal is something like carrying out a particular set of operations safely and profitably."

Another best practice is to avoid using the P&ID diagrams as an organizational template. "The operator was never considered in the P&ID design," says Krajewski. Instead plan screens that are have a logical hierarchy and help the operators do their jobs.  "Operators shouldn't have to go through ten or 12 screens to get the information they need," said Krajewski.

Some of the elements of the well-designed screen seem like a step backward. HMI screen designers need to avoid taking advantage of the hundreds of color options available, the animations, and the 3-D renderings. They look cool, but they are confusing and don't convey any useful information, said Krajewski.

"A good HMI screen is boring," he said. Hence the newest screens tend to be in gray scale, or at least in a single color palette, so that multiple colors don't confuse the operator.

Krajewski recommended that when colors are used, they should invoke the "pop-out principal." This is the effect that occurs when a limited number of important items are highlighted in color against a neutral background. The eye is drawn to those items and everything else fades into the background.

Colors also should be consistent across all the screens. If red is the color used to indicate an alarm condition, then it cannot be used for any other function. Alarm signaling also should be consistent across all screens and indications should be redundant. For example, alarms that require immediate attention might all be red and indicated with a square box with a number 1 in it. Alarms that can wait 30 minutes for attention might be indicated by a yellow triangle with a 2 in it.

Context is everything in HMI screens, added Krajewski. "Simply presenting a value by itself is meaningless. It's just a number." Rather, the operator should be able to see how far the number is from the setpoint, how close it is to alarming, and whether it is inside the normal operating range. Bar charts or trend charts that show the number in relation to those critical benchmarks are much more useful than just the numbers themselves.

Krajewski admitted that selling management on spending the money to upgrade HMIs and selling operators on giving up familiar, if inconvenient, systems isn't easy but can be done. The business case revolves around poorly performing systems that can cause accidents and poor performance. High-performing systems are essential to maximum efficiency which in turn drives savings on energy, raw materials and waste.


Furthermore, in the future, said Krajewski, "the operator will be a business manager, tracking the use of materials, energy and raw materials. He will be making decisions about them in real time and will need those KPIs for correct decision-making."

For gaining operator acceptance, Krajewski recommended installing a couple of the new high-level screens first and keeping the old system for other screens. "Once operators get a chance to work with the new ones, they see the advantages and begin demanding them," he said.

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