A human-machine interface (HMI) is not defined by 3D graphics or fancy animations. Unfortunately, these are the first features HMI manufacturers show during demonstrations. When following the high-performance HMI philosophy, one must forgo the 3D graphics and fancy animations to focus instead on displaying applicable and accurate information.
Three-dimensional graphics should be ignored completely since they do not serve any purpose for the control of the machine or process. Animations are also useless in most cases. Consider automobile controls. When you step on the accelerator pedal, do you need to see an animation of wheels on the dashboard to know that you are moving? While the answer is no, I am sure many will think this is a cool idea. Such animation would not help you control the car in any way. Instead it creates a distraction and takes away space that could be better used to make a bigger speedometer or fuel gauge.
When deciding on what information tp display, one must be very careful. While information is data, data is not information. Let’s go back to the car example. The fuel gauge shows the remaining fuel. This is elegantly achieved with a scaled analog gauge with a high limit (F) and a low limit (E). Even the most modern cars, with graphic dashboards, still emulate the analog gauge or have a bar graph. When designing an HMI, don’t just throw data on the screen, instead, display the data in a way that the operator needs only a quick glace to know what is happening. That is information.
Below are some of the best practices I follow when designing an HMI.
- Use light gray backgrounds. This helps eliminate eye fatigue, glare and other issues.
- Use dark gray or black foreground for vessels, process lines, etc. If emphasis needs to be made on any object, make the line thicker rather than a different color.
- Stay away from using color to identify a product, such as white for steam or blue for water.
- Use black for static text. For dynamic text or values, use bold dark blue. This helps differentiate it from descriptions.
- Use colors such as red, green and yellow for abnormal conditions only.
Designing a high-performance HMI requires a well thought-out design. Don't just throw indicators and buttons on a screen and call it an HMI. HMIs shoudl be designed to promote safe operation of machines and provide operators with accurate information. Fancy 3D graphics and animations belong in video games, not HMIs.
Juan Escolarte is control systems engineer at Loman Controls Inc., a certified member of the Control System Integrators Association. Learn more about Loman Controls on the Industrial Automation Exchange.