You might have HMI design backward

Did you know background color is the least important element?

By David A. Strobhar, PE, Center for Operator Performance

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I’ve heard many comments and discussions in the past few years regarding the color grey. Is that even a color? I’m not talking about the 50-shades-of variety. The use of a grey background on process graphics has become all the rage, or rage-inducing, depending upon with whom you are talking. Is background color on a display so powerful that it can, by itself, radically improve operator performance?

There are other elements of HMI design, so where do they fit in? If you rely on more than five decades of human performance research, I would argue that the order of importance for the elements of HMI design would be as follows, with background color the least important of them:

1. content

2. organization

3. layout and formatting

4. color coding

5. symbols/shapes

6. number and size of monitors

7. background color.

Many people would likely have ordered this list the reverse of what I have. Their upside-down view of which elements are important in HMI design likely stems from a misperception of what HMI design is all about. People often think display design is fundamentally a visual issue. It’s not. HMI design is about information transfer: transfer of information from the process to the operator at the console. As such, the key concern needs to be how to transfer information, not visual representation of objects.

An easy way to think of this is storytelling, an analogy put forth by Don Norman, one of the pioneers in human factors. In telling a story, you’re trying to transfer some information. There are a variety of mediums for doing this—verbal, print, movie, play. While the medium can aid the transfer, it doesn’t in itself result in the transfer. The best prose, pictures or visual effects do not a great story make. Similarly, the best shapes, dynamos and color do not a great HMI make. Fundamentally, the success of the transfer depends upon the content.

Also read: Go back to basics with HMI design

This focus on content was emphasized in one of the first projects funded by the Center for Operator Performance, which is a collaboration of operating companies and DCS suppliers based at Wright State University in Dayton, Ohio. In conducting a project on color usage, Dr. Jennie Gallimore pointed out that, while poor color coding can hinder performance, it is proper content that is essential to performance. If the correct content is present, albeit with poor presentation, the task can likely still be performed. However, if the content is absent, task failure is almost guaranteed regardless of the presentation.

Many people would say that the content for the HMI is determined by the I/O of the process. It’s not. The I/O constrains the content, just as the events in your life constrain your biography. However, a biography that contained every event in your life presented with equal weight and detail would be both very long and very dull. Similarly, a good HMI design entails selection and organization of those I/O relevant to the tasks required. This selection and organization can and should be the longest part of the HMI design process. It not only is necessary to ensure good HMI design, it speeds the subsequent display design efforts and minimizes rework.

While many an operator has maintained that they do use all their monitors, it is surprising how often you will find the same display on multiple monitors.

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