Optimizing your HMI on the plant floor

The benefits of optimizing a human-machine interface (HMI) include increased worker safety, improved production, and reduced time needed to make critical decisions if the data presented on the screen is clear, concise, and easy to interpret in real-time.

01/28/2015


Plant workers use human-machine interfaces (HMIs) to provide them with real-time virtual data on the manufacturing processes happening around them. When used properly, an HMI is an invaluable tool that allows the operator to take decisive action before a problem occurs. Sometimes, though, an HMI doesn't provide that information. This usually happens because the HMI provides too much information with too little context or the information on the screen. Speaker Travis Cox, director of training and sales engineering for Inductive Automation, offered some advice for users to get the most of their HMI with the webinar "Design Like a Pro: Optimizing Your HMI." CSIA co-sponsored the webinar with Inductive Automation, a CSIA Partner member. The benefits of optimizing an HMI include increased worker safety, improved production, and reduced time needed to make critical decisions. After all, Cox said, manufacturers invest millions, even billions, into their HMIs.

Reducing visual clutter and distractions, Cox said, is key to an effective HMI. If there's too much data and too many visuals clogging the screen, it might take an operator several hours to know something is wrong or the operator might not notice at all. An effective HMI will keep the screen simple and will present the data in a context that is easier for the operator to understand. Graphics are also important, but Cox stressed that the graphics should focus on helping the operator.

When it comes to displaying data, Cox stressed that it should be in a context that is simple enough so the operator can assess situations just by glancing at the screen. Moving analog indicators and a radar chart/spider chart are two examples of presenting data in an analog form that is easy for an operator to understand because they clearly present the information and the parameters so the operator can make adjustments as needed.

Establishing a consistent hierarchy for an HMI, Cox said, is important because it provides a progressive exposure of process detail. It helps reduce clutter and makes things easier for the operator.

How the data is presented is also important. Emphasis, when used properly, helps operators find what they're looking for more quickly, Cox said. Color, position, size, and isolation are four ways to make data stand out on an HMI screen.

  • For color, the screens should be neutral and monotone, and bright colors should only be used for alarms rather than normal conditions.
  • For position, the most important information should be presented on the top-left part of the screen and the last important information in the bottom-right because people in Western cultures read top to bottom and left to right.
  • Larger objects on the screen will stand out because the human eye notices anything that breaks the pattern.
  • Isolating items can be effective in helping operators focus on what's important. This works best when the HMI screen isn't cluttered with other data.

Being able to trend and predict data on an HMI screen is also useful for operators, Cox said. It's hard for operators to work effectively when they're only seeing current conditions. Trends can show what conditions have been, where they are now, and where they're likely heading. Cox also talked about embedded trends, which are recommended for important information and key performance indicators (KPIs).

While no HMI is ever perfect, Cox emphasized that, whenever possible, it should be easy for the operator to use from both a production and a safety standpoint.

- Chris Vavra, production editor, Control Engineering, cvavra@cfemedia.com 

Key concepts:

  • A good HMI allows the operator to make decisions in a timely, efficient manner.
  • How the data is presented on an HMI has a huge impact on how the data will be interpreted by an operator.

Consider This

When using an HMI, does the screen follow all of these tips or just some of them? Which of these tips works best for you when trying to interpret and analyze information on the screen?

ONLINE Extra

For more help with HMI design, see the Control Engineering articles linked below.



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