About 40 attendees heard Paul Gruhn’s presentation on the human machine interface (HMI) for plant operators at the March 18th meeting. Gruhn, a professional engineer, an ISA Fellow, and Rockwell’s Global Process Safety Consultant, first explained how badly designed screens can lead to disasters. He said they often contain too much information, too many colors, and worst of all, animation. The result is distraction rather than information. First the operator needs to know if the plant is running as expected, with alerts to any exceptions to the normal.

Gruhn provided guidance for designing operator displays, showing examples of what works and doesn’t work. Complex P&ID graphics, for example, are not the answer but the problem. Colors are often distracting and inconsistent. Trends, on the other hand, would be helpful. The goal is to help the operator predict and prevent problems, not react to them after something goes wrong. Gruhn also said that plant management should provide style guides for operator displays to instrumentation and control vendors. For a PDF of the slide presentation, click here. — Jim Talbot