Quick Tips for HMI Development

Although developing a human-machine interface (HMI) is often the last part of a control-system-integration project, it’s vital to the success of an automation system.

According to Justin Gilg of systems-integrator Huffman Engineering Inc. (huffmaneng.com, Lincoln, NE), a successful HMI design requires restraint. He offered the following tips.

Consistency

In most cases, new HMIs, should be modeled with the look and functionality of others in use at the site. Consistency is key, from screen to screen and from machine to machine. For example, if the menu appears across the top of existing HMIs, follow that format. The same goes for other aspects of the display. Uniformity is important for new-employee training and the ability of operators to move to unfamiliar equipment.

Developing HMIs for facilities that don’t already have them is another matter. This situation allows for more creativity, as well as reliance on experience with similar applications. Consistency in menu placement, color scheme, and graphics from screen to screen is still crucial.

Color

If the site has a standard for color, adhere to it. If not, there’s usually an industry standard. Limit the use of color so that it effectively captures operator attention. Colors designated for alarms should only be used for that purpose so as to not minimize their significance. Color should not be the only discriminator of an important status condition. Use text to call it out. For example, compliment the red-color button with the word “stop.” To draw attention to alarms and faults, consider adding blinking.

Don’t overlook the possibility of color blindness in operators. Red-green color blindness is the most common type, particularly for males, followed by blue-yellow color blindness. If it’s necessary to use these color combinations together, make one a dark shade and one a light shade so they are more distinct.

Graphics

High-performance graphics should improve an operator’s situational awareness, not be a distraction. While access to an abundance of data is alluring, use it judiciously. The goal is to make the process easier for operators, not to overwhelm them. Fancy or overly detailed graphics showing every part of the machine can become clutter and lead to confusion.

Simplicity

Keep it simple. Display only what operators need to know, and make the data useful. Don’t expect operators to know what a process value means. Instead, 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. Finally, consider the number of screens with which an operator must contend. Adding too many can hamper operator control.

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