When developing HMI screens, realize that you are attempting to capture the essence of the machine or process, not just posting key automation variables and control mechanisms. Operational feedback is vital for efficient HMI screen layouts. Think of yourself as an artist, commissioned by manufacturing operations to create the HMI screens.
1. Less is more. It’s important to keep the HMI simple and with the operator in mind. It’s best when it’s self-explanatory and easily understood. Also, try to make the pages similar and follow the same page layout throughout. Avoid making the display too technical. It’s normal for engineers to try to give the customer everything, but with HMI, less really is more.
2. Right-size displays. Don’t try to save money by selecting an HMI display screen that’s too small. It’s also important not to cram too much information onto a screen. Size the display according to the amount of information that is most important for the operator to see. Always discuss requirements with the equipment’s operators well ahead of time, not just with their managers. Operators usually have different needs and the success of your system depends on their usage.
3. Design tips. A good design requires careful use of layout, color and content. If you get it wrong, your operator misses an indication, you lose money, or worse, someone is injured. The ”bad” screen is less than satisfactory: The layout is poor, the plant representation isn’t logical and the screen layout makes it difficult to locate the data. Poor selection of colors, excessive use of capitals in a serif font and repetitive use of units with all data values makes this a really difficult screen to read—especially at a glance or from a distance. Avoid colors that could create problems for people with color blindness. Minimize the use of colors to allow actual device state and alarms to stand out. For alarming, choose colors that contrast with the normal process view so the operator will notice the change.
4. Plant review forum. Hold a design review with a group of plant personnel to discuss any status notifications, events, alerts and alarms that need to be programmed, both from the perspective of an audio-visual action and an operations response. Step through the intended functional system, once as the designer, once as the user and then invite at least two levels of users who will be interfacing with the HMI. Doing this prior to specifying equipment helps to identify the features that users will want in the HMI station. It also avoids surprises at point of commissioning.
5. Location, location, location. Real estate can be prime in a busy production area. Locate the HMI in a practical place, out of heavy traffic areas but accessible. Be aware of near-future projects in the area. Guard the HMI location so others don’t park or configure something else on top of the station.
6. Back up work periodically. Backups are especially important before implementing upgrades or changes. Software such as Norton’s Ghost Image can be invaluable to support and maintain HMI systems.
7. Visualize the process. HMI graphics should illustrate the production process in the plant to provide better visualization to the operators, giving them a sense of the action that’s required. Use hardware that meets minimum requirements and keeps the number of failure points low and assures high availability of the system.
8. Only essential data. Make control and monitoring of the process simpler by selecting only the most essential information from the process database for the historian. This will reduce the load on the system and keep it from stalling or failing. Don’t forget the need for maintenance and make sure you schedule periodic backups.
9. Think about flow. It is essential to have a clear design approach to the HMI. Decide how the display blocks naturally flow and how sections need to be grouped together for the operator. Do not blindly follow P&I diagrams. The S88 functional hierarchy is a good place to start. Make paper-based designs to get a feel for screens, navigation and other requirements, and review with clients prior to designing and making electronic screens.
10. Alarm strategy. Alarming needs to have a well-articulated strategy. Alarms must be used for conditions that require intervention and must have a clear corrective action associated with each one. Anything else should not be an alarm.
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