Digital Controls Deliver Diagnostics, Maintenance and Troubleshooting Benefits

Are Your Controls Digital-Healthy?: The Growing Use of Fieldbus, Ethernet and Wireless Means More Opportunities for Diagnostic Tools and Monitoring, but How Do You Diagnose Your Digital Controls?

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By Mike Bacidore, Managing Editor

The significant upside of the diagnostics, maintenance and troubleshooting benefits that a digital network provides is all too alluring to ignore. Digital diagnostics provide more and better information that helps to troubleshoot and fix problems, and without shutting down the entire system.

Eric Rice, director of technical support for North America at FKI Logistex (www.fkilogistex.com), Cincinnati, which designs and builds conveyance and palletizing machines, agrees that, from a cost standpoint, the digital network makes a lot of sense.

"You don't really gain anything in speed because the digital network is a little slower," he explains. "But the amount of diagnostics you have is better. If you have an issue in one part of the system, it doesn't mean the entire system is down. Subsystems can run independently, and you have more uptime. In today's conveyor system, digital networks are the lifeblood."

Digital Troubleshooting

With the unstoppable wave of digital adoption, diagnostics have changed, but only slightly. "Our products' digital signals consist of 24 Vdc I/O signals and Ethernet I/P," says Wade Peterson, electrical engineer at CMD, builder of bag- and pouchmaking equipment in Appleton, Wis. "Typically, digital signal problems for us are rare as our machines have a very small footprint and the cables are well-shielded and isolated from noise. Most problems are typically wiring-related like a broken conductor or nicked insulation. Our troubleshooting methods therefore focus on the media first."

The best first step could be going a visual inspection, says Jack Chopper, chief electrical engineer at Filamatic (www.filamatic.com), a liquid filling and packaging machine builder in Baltimore. "Fortunately, we don't encounter very many digital signal problems, but we'll use network analyzers and testers, both hardware and software, built-in diagnostic tools, recording instruments, multimeters and scope meters."

The tools of choice seem consistent from machine builder to machine builder. "We typically troubleshoot with a combination of multimeter, oscilloscope and PC-based tools," adds Peterson.

From a discrete troubleshooting standpoint, the most frequently used equipment at FKI Logistex is a multimeter. "Those kinds of checks are done on-site," says FKI Logistex's Rice. "From a network point, different buses have different values we look for. For a Profibus network, we have a Profibus monitor. We look at the integrity of the network. We can do the same thing for Ethernet. We also have some proprietary networks that have resistance values. If it's out of specification, you may see intermittent issues with that piece of equipment. We have Ethernet sniffers—software or hardware—we would use to troubleshoot or get statistics."

At MAG Americas (www.mag-ias.com), it's done in two different ways. "In the machine realm, for qualification, some tools are provided by our manufacturers like Fanuc or Siemens," says Jim Braun, vice president, product development and standardization for MAG, a large machine tool and systems company in Hebron, Ky. "We have other devices for tuning. We have Heidenhain scales. We have devices we can insert in the signal path or in the network—Profibus or Ethernet. That's primarily on the machine qualification side. In the field, we have internally based diagnostic tools that run on the controls and give some pass/fail indications. We're also looking at some other more advanced tools we haven't released yet, like having a built-in scope feature inside the control." MAG uses a lot of Profibus and Ethernet-based interfaces that are proprietary to the control, and other parts of the machine may take special types of equipment, too (Figure 1).

"During the building and qualification of the machine, we have some tools to debug the machine," explains Braun. "Once the machine is finished and it ships, if there would be a problem, we have remote diagnostics, but it's only available on PC-based controls where we can request control of the machine and the person on-site can give us control."

Digital Diagnostics

Most digital signal protocols include some form of error-checking or diagnostic information, explains Mara White, industrial Ethernet marketing manager at Fluke Networks (www.flukenetworks.com). "The more intelligence or sophistication built into the diagnostics, the more complex the measurements and analysis algorithms become," says White. "This has an exponential impact on cost and can even lead to compromises in network performance. It is the compliance to digital protocol standards and the built-in diagnostics and error-checking that allow machine builders to integrate various subassemblies. This can be very effective for the non-custom jobs but also protects them when the line of transfer of ownership becomes an issue."

When integrating multiple machines from a variety of vendors, use a combination of built-in machine diagnostics, diagnostic tools and appropriate maintenance strategies to ensure optimum system performance, says White. "Relying solely on the machine's diagnostics for equipment breaks can be a risky proposition," she warns (Figure 2). "Testing and troubleshooting comprise a small cost that can save numerous hours and headaches during the initial troubleshooting and ongoing maintenance of the machine and network. And the value increases with the mission-critical and time-sensitive nature of the work."

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