11 tips for an effective HMI

Published on 22 May 2022 Reading time : 8 Minutes

There are many different ways to develop HMI screens for machine and process automation applications. An effective structure requires discipline in the design. The feel, appearance and ease of use of an HMI can vary widely. This is because of all the tools, object libraries, animations and colors available on modern HMI software. However, there are standards to improve HMI effectiveness.

These standards can serve as a basis for establishing internal HMI design guidelines, which in turn can be used to create consistent and effective HMI displays from one machine or process to another. Standards are important and users should consult them before final implementation of an HMI design, but they can be difficult to read and interpret. The tips below are intended as design aids.

1. Storyboards are a good start
2. Talk to operators
3. Use color and animation wisely
4. Add charts
5. Display matching image
6. Keep important items together
7. Provide situational awareness
8. Limit the number of clicks per screen
9. Beware of pop-ups
10. Use date and time stamp logging
11. Create a style guide

Tip 1. Storyboards are a good start

A good starting point for an HMI design is a text based on the overview of the proposed content of each screen. For operator and ease of use, the designer creates storyboards for the main screen, equipment status screens, setpoint or recipe screens, manual functions, message displays, fault displays and other subsidiary screens. The designer can then convert these text contours into a storyboard for each screen. The storyboards should emphasize dynamic images such as status indicators and should contain repeated images.

Tip 2 Talk to operators

When creating the storyboards, ask yourself what is most important to the operators. But even better is to ask if the operators are available for consultation. More data on screen isn’t always better, so don’t overload the operators with information. In return, focus on their tasks and what it takes to understand the machine and the process. Present the information in such a way that the overall company status can be understood at a glance. Then have an experienced operator review the proposed storyboards.

Use a prototype of the HMI in time in the design cycle and see how the operator uses the interface. If this is not possible, use the storyboards for a pilot operation session with the operator. Look at tricky situations where an operator struggles to interpret what he or she sees, and look at the number of actions required to complete a common task. Are there extra features you can add to relieve the operators of unnecessary button presses or otherwise make them more efficient?

Finally, it is important to ask the operators for their advice and opinion, but filter their comments. They may not always see the big picture. Never forget that you build the HMI for their use, so their input is very valuable.

Tip 3. Use color and animation wisely

HMI guidelines recommend limiting the use of color and using low-contrast gray backgrounds. This is to make the screens less cluttered. For example, a light gray screen background, where a typical indicator would be dark gray in the off position and white in the on position, is pleasing to the eye and intuitively logical, because a light bulb turns white when lit. So generally use muted colors or shades of gray and use bright/saturated colors to indicate different conditions.

Be careful when developing graphics. Do not use too many colors and graphic animations available in the software, this should be avoided. Animate only if it makes the operator more efficient.

For example, using animation to show the position of a part on a transfer line can be an efficient and quick indication of production status. However, showing a pump motor running is distracting if the screen’s intent is to show only high-level fault indications.

Tip 4. Add charts

The purpose of every HMI screen is to develop situation awareness among the operators. In other words, the ability to identify the process and understand the important elements of a situation. To raise awareness, displaying in schematic form will help and be an important factor for design on an HMI display.

Operators understand the meaning of an image faster than a piece of text or the status of a group of colored buttons. And when there’s a language barrier, images become even more important. With most HMIs it is possible for objects to overlap

ppen, so consider that a small image may overlap a button. But limit their use or isolate them on alternative displays or it may slow down the performance of a particular display.

The display of data is important in HMI design and different types of data require different display types. A number on a screen can accurately represent the speed, but the engineering units can be questioned and the acceptable range is unknown. Solve this by adding the following units, for example centimeters per second, and tabulating the maximum and minimum values. A line graph with a trend function can display past and present data and is a good indicator of future values ​​because an operator can quickly see that the values ​​are moving towards an upper or lower limit.

Tip 5. Display matching images

An image of the machine, the process being controlled or other realistic depiction can be very helpful and can help the operator understand the location of problems such as faulty sensors or blocked actuators.

By using clear pictures of the machine, location indicators and arrows to the valves and hatches that must be opened to clear a fault. Can be guided to the fault location in seconds. But resist the temptation to only import design drawings and diagrams, as that often results in a busy screen with an abundance of details.

Tip 6. Keep important items available

Save a portion of the screen for important items such as start, stop, and important setpoints. This way, the operator immediately knows where to look for this critical information. A strip can also be placed above or to the side of the controls. Just make sure that this area is completely consistent and displayed on every screen.

Most HMI software packages provide a background screen feature that allows designers to create, edit, and maintain such an area at a location in the project layout. It can then be displayed on multiple screens.

Tip 7. Provide situational awareness

Ensure relevant data is clearly displayed so operators can see the current state of the machine or process at a glance. A good display answers two important questions: “What state is the machine or process in now?” and “How does that relate to optimal conditions?”
In addition, the HMI screens can be divided into four basic groups, which can make things even clearer for the operators:

Tabular and text based screens: lists or tabular groups of data and status values
Schematic screens: data is displayed on schematic diagrams of the current process
Trend screens: current and historical data values ​​displayed on graphs with time
High Performance Displays: Actual data supplemented with basic graphical elements to convey additional information
For simple machines, it may be sufficient to display data related to the current state of the machine, but for more complex machines or processes, the screen design and layout should aim to help an operator foresee potential problems.

Tip 8. Limit the number of clicks per screen

Keeping all screens within two or three clicks of the home or main screen is essential, considering how the workflow might apply. Ask questions such as which tasks are performed most often and which are the least. With this knowledge, optimize the layout to be as efficient as possible.

Keep screen menus and screen switching actions as accurate as possible around the application and always leave a clear path so that even the least experienced user does not get lost in the menus.

Tip 9. Beware of pop-ups

Don’t use too many pop-ups on an HMI. It is not intended that a series of pop-up error messages appear on the screen and must all be acknowledged one at a time before the operator on the screen can solve the root cause.

Tip 10. Use date and time stamp logging

In addition to a good HMI design, it is also important that alarm and event logging is used in a smart way. Record the alarms and events when they occurred. Recurring problems often seem unrelated, but often related to shift changes, equipment startup or shutdown, breaks, or other periodic factory activities.

Alarm acknowledgment requirements show how quickly operators respond to conditions. For example, if responses are slow, you can refine the layout or design of the HMI to make them respond quickly.

Tip 11. Create a style guide

Make one together
following common styles for constancy between all HMIs in your and multiple plants. By using charts, trend objects etc consistently, the operator understands it better and becomes familiar with it. It is useful to find HMI software packages that offer object libraries and screen libraries for storing and sharing successively proven elements or entire screens. This allows you to easily reuse the same items for multiple projects.

Use these tips to develop HMI design guidelines and use these guidelines to create consistently effective displays from one project to another.

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