Fieldbus Reigns in Process Control
October 2007 (p.42)
Written by Rob Spiegel, Contributing Editor
After nabbing the savings from easier installation, plant managers are beginning to use fieldbus for asset management.
Plant managers at the water plant in DeKalb Country, Ga., learned about the benefits of fieldbus networks quickly when they installed Profibus in their new water plant. They were so pleased with the results, they retrofitted two existing wastewater plants with the fieldbus. “It makes your life easier,” says Merat Zarreii, F&T Division manager at the DeKalb County Department of Watershed Management in Stone Mountain, Ga. “With fieldbus, I can interrogate the device from my office and get a flag if it needs maintenance or replacement.”

At the retrofitted plants, DeKalb already had Siemens control technology, which made the network communications simpler. “It wasn’t difficult to change over from analog,” says Zarreii. “Our technicians really took to the new technology and were comfortable with the change.” One of the biggest changes was the ability to change devices only when they show a problem. “We were changing out devices on a schedule before,” says Zarreii. “Now we can pinpoint what needs to be done, so we spend much less.”

Part of the ease in shifting to fieldbus was the training that DeKalb’s technicians received. “We got training from Profibus Trade Organization (PTO),” says Zarreii. “I have eight certified technicians at the plant. We even trained those technicians who have two-year degrees.”

Surprisingly, the most difficult part of the switch to fieldbus was convincing the engineering company overseeing the project to take on the digital network. “Most of the engineering companies we talked with didn’t have a lot of experience designing and installing fieldbus,” says Zarreii. “They were very limited in the design of fieldbus systems.” Zarreii persisted with pressure. “I had to twist their arms. We told them, ‘Either you do what we want or we’ll find somebody else.’ ”
Most plants implementing fieldbus technology first look to the installation savings as a justification for the switch. In recent years, however, process plants are looking for the deeper benefits of asset management. In many cases, the asset management gains come later. Often, the plant installs fieldbus to save on wiring and configuration but doesn’t get around to monitoring devices for health until much later. Recently, plant managers started to adopt fieldbus specifically for asset management and predictive maintenance. They want the big savings—fewer plant shutdowns.

Installation Savings

Even if installation savings are not the most significant benefit of fieldbus, they still matter. Those savings are often the impetus to adopt, because those savings can convince the bean counters that the project is worthwhile. “One of the biggest benefits I’ve seen is the ability to configure devices while sitting in the control room,” says Moin Shaikh, distributed control system (DCS) consultant at vendor Siemens Energy and Automation Inc., in Alpharetta, Ga. “In the old days—and still in many places—people go to the device with a handheld tool to configure it.”

Installation savings is one of the big reasons JV Industrial Companies pushes fieldbus. JV Industrial, of Laporte, Texas, is a contractor for industrial power plants. At first, company managers found their customers were skeptical of fieldbus networks. They were won over by the installation benefits. “They were leery of fieldbus at first, but they saw some benefits on the cost of wires and installation time,” says James Goodman,