Diagnostic Tools Are Only As Good as the Display That Operators See

HMI Plays Role in Diagnostics: Engineers Can't Troubleshoot Problems Without an Operator Interface That Tells Them What's Wrong

Mike BacidoreBy Mike Bacidore, Managing Editor

Many companies use HMI to view feedback and real-time data from controllers, often using it to monitor the voltages, currents and frequencies of some equipment and for diagnostics to help troubleshoot equipment. "The most important thing the system can provide is the feedback on the HMI," explains Eric Rice, director of technical support for North America, FKI Logistex, a Cincinnati division of Intelligrated (www.intelligrated.com). "Our system is designed to pinpoint a device that has an issue. It can provide instructions or refer to our production manuals to resolve the issue. We have a feature-rich HMI on our systems that can bring up an alarm."

The initial feedback provided by an HMI is often the first step in determining where to start looking for the problem, says Hilton Hammond, product manager–ScopeMeter, Fluke (www.fluke.com). For example, if the reported problem is an "under voltage" condition, the maintenance engineer would start at the branch feed circuit, using a multimeter or power quality analyzer to verify the line power input is within specification and work his way through the system, says Hammond. "Often the diagnostic algorithm built into an HMI can detect a problem, but given the complexity of today's integrated systems, that problem might be beyond the scope of the HMI."

The more information, the better, agrees Jim Braun, vice president, product development and standardization for MAG Americas (www.mag-ias.com), in Hebron, Ky. "Some of the stuff we're looking at goes beyond the normal identification of where the fault might be," he explains. "We're interested in what happened in that machine when the fault occurred. We want to be able to capture that data. If one of the servo axes failed and we had a misposition problem, we'd want to know what went on, what program was running, and the position of the axes. We use that to improve reliability, and also to better understand the operating life of some of the systems in the machine. We can have counters that monitor how many times we did a tool change or how many linear meters of travel a particular axis has gone."

Because of the competitive manufacturing environment, being able to pinpoint a problem through automation and lead the user through to a resolution is an opportunity, says Jack Chopper, chief electrical engineer, Filamatic (www.filamatic.com), Baltimore. "Unfortunately, this effort is sometimes less than perfect, but the ability to direct the user to a group of components or a particular area that's in trouble is often all that's required," he explains.

"With the memory in today's OITs and HMIs, it's possible to overwhelm the operator with detail," says Wade Peterson, electrical engineer, CMD (www.cmd-corp.com), in Appleton, Wis. "We try to balance this by creating error messages that are meaningful and allow the operator to know if it's something they can address or something they need to call maintenance for."

Resolution instructions are harder to implement, explains Peterson. "More and more of our products are sold around the world, and translation can throw twists in troubleshooting guides," he says. "For example, text translated from English generally takes up more space, which can cause issues with fixed-width columns on OITs. Because of this, we still rely very much on language-specific manuals and PDF files for troubleshooting information."

A properly developed HMI is not possible without knowing what is happening at the core system level, contends Corey McAtee, product manager, Beckhoff Automation (www.beckhoff.com). "A dynamic HMI that can report, ‘fieldbus cable 2 on I/O node 3 has a line break and motor 5 is overheating' is leaps and bounds easier than thumbing through dog-eared manuals stuffed into clunky three-ring binders," he says.

"Given the complexity of today's production control systems, an HMI or even a well-trained engineer cannot possibly understand and cover all the variables, system permutations and possible error conditions that might occur," contends Hammond. "A more practical approach is to provide the troubleshooting staff with test tools that can interpret the situation and provide meaningful feedback to the user. More than simply stating that a problem exists, a good diagnostic tool can tell why the problem exists and, even more useful, what needs to be done to correct the problem."