The High Performance HMI

This is an excerpt from the November/December 2012 InTech feature by Bill Hollifield. For the entire article, please see the link at the bottom of this post.

Almost three decades ago, we control engineers were given a new task for which we were ill-prepared. We installed control systems with the capability to display real-time process control graphics for the operator. But the screens were blank, and we were responsible to fill them up.

We had no available guidelines as to what constituted a “good” graphic. So, we did the best we could with what we knew—which wasn’t much! As a result, we set in place a low-performance paradigm of what a control system human-machine interface (HMI) should look like, and inertia has done the rest. Mostly for convenience, we chose to depict the process as a P&ID view covered in live numbers. We stuck with that paradigm even as graphic capabilities of DCS/SCADA systems improved, mostly migrating rather than redesigning the displays. Now, tens of thousands of operators throughout the world are controlling multi-billion dollar processes by looking at primitive cartoons designed at a time when we really did not know what we were doing.

Poorly performing HMIs have been cited as significant contributing factors to major accidents. The principles for designing proper process graphics are now available. A high performance HMI (HPHMI) has many advantages, including improved operator situation awareness and process surveillance, better abnormal situation detection and response, and reduced training time for new operators. Many industrial companies have graphic improvement efforts underway.

High performance displays depict information. Information is data, in context, made useful. HPHMI graphics show not only the process value, but where it is relative to “what’s good.” Abnormal conditions are designed to stand out clearly. Color is used consistently, effectively, and sparingly. Graphics are designed with a proper hierarchy.

Displaying information

In Figure 1, much money has been spent on the instrumentation. But can you answer the simple question, “Is this process running at peak efficiency, or very poorly?” To know that, one must have specific training and months of experience in normal and abnormal situations. The operator must compare each number to a memorized mental map acquired through experience and upsets. This is a difficult cognitive process. Most operators have well over a thousand such numbers and status indications spread out over dozens of graphics. Detecting abnormal conditions is difficult.

To read Bill Hollifield’s full article, click here.

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