Although a Human Machine Interface (HMI) is often the last part of a control system integration project, the HMI is vital to the success of your automation system. There are countless guidelines, standards and handbooks covering HMI best practices and design including those published by ISA, ASM, and ISO to name a few. Nonetheless, with the abundance of data available and advanced software tools, high-performance HMI development requires restraint in design. Here are 5 tips you should keep in mind when programming your HMI for the best results.
Tip 1 – Consistency
If there are other HMIs in the plant, you need to start there. In most cases, you will want to model the new HMI to be consistent with the look and functionality of other HMIs presently used in the plant or facility. Consistency is key, from screen to screen and from machine to machine. If the menu appears across the top on the current HMIs, you need to follow that format. If there is a color format used for particular functions, this needs to be adhered to as well. Uniformity is key both for new employee training and the ability of operators to move to unfamiliar equipment as needed.
Developing an HMI that is a completely new enhancement for a facility allows you to be more creative, relying on your experience with HMIs developed for similar applications. However, you will still want consistency in menu placement, color scheme and graphics from screen to screen.
Tip 2 – Develop an Outline and Involve the Operator Early
Start with an outline of the process the HMI will monitor and control. From there, develop the HMI outline with the information and objects to be displayed on each screen for the HMI. The HMI outline is a great tool to make sure you are headed down the right path to accomplish everything needed for the HMI’s optimal functionality. Review your outline with management, but don’t stop there: involve the operator as part of this process. With the outline established, ask operators if any information they need to do tasks easily and successfully is missing.
Tip 3 – Color
If the facility has a standard for color, you need to adhere to that standard. If not, there is usually an industry standard. However, it is important to limit the use of color to be effective in catching the attention of an operator. Older HMIs often had black or bright blue backgrounds, the new thought is to use a light gray background to minimize glare. Colors designated for alarms should only be used for that purpose as to not minimize their significance. Color alone should not be used as the only discriminator of an important status condition. Use text to say what it is. For example, compliment the red color button with ‘stop’ in text. For alarms and faults, consider adding blinking to draw attention to it.
Color blindness is another factor that should not be overlooked. People with color blindness aren’t aware of differences among colors that are obvious to the rest of us. According to the National Eye Institute, 8% of men and 0.5% of women are colorblind. With nearly 70% of the manufacturing labor force being male, color blindness is not to be ignored. Red-green color blindness is the most common, followed by blue-yellow color blindness. If it necessary to use these color combinations together it is best to make one a dark shade and one a light shade to keep everything more distinct.
Tip 4 – High-Performance Graphics
Consider high-performance graphics techniques. The industry is trending away from HMI screens filled with fancy, colorful graphics. High-performance graphics should improve the operator’s situation awareness. High-performance may sound like you want every little detail displayed, but high-performance requires simplification. While access to an abundance of data is alluring, use data discriminatorily. Your goal is to make the process simpler for the operator, not to overwhelm them. Consider the purpose of the HMI. Fancy or overly detailed graphics showing every part of the machine becomes clutter and will make it more confusing and difficult for the operator to find the important data.
Tip 5 – Keep it Simple!
Bottom line, to build a high-performance HMI, display only what the operator needs to know. Make the data useful. Don’t expect the operator to know what a process value means, show where it is relative to a good process value range. Abnormal conditions need to be obvious. Color must be used sparingly, consistently, and effectively. Another consideration for keeping it simple is the number of screens the operator needs to interface with. Adding too many screens can hamper operator control; you do not want the operator to have to bounce around too many screens to resolve an issue.