Fieldbus Wars continue

Rossi, of Mead Johnson, reports that he’s used AS-interface and Profibus. “We've used AS-i, and as ‘easy’ as it is purported to be, we got bit by low-power dropouts on solenoids,” he says. “We’re using Profibus protocol to communicate with Mettler-Toledo scales, and have been happy with the results.”

Marcelo, of Nestle, doesn’t care which fieldbus he buys, as long as it works. “The feature that I want most is plug-and-play,” he laments. “When we first installed a fieldbus in our factory, the project engineer spent hours configuring and reconfiguring. Then, one day, a whole line of instruments stopped working. The engineer had to reenter the configurations one by one. The claim was that you'd only need to reload the configuration file, but that didn't work. Having experienced this, I'd want a system where I could get a pre-calibrated instrument, set its address, connect it to the fieldbus, and I'd be up and running. No need for setting up configurations or setting up communication parameters.”

Bradford, of Concept Systems, adds, “If the people designing instrumentation systems ever had to actually install and use them in a real plant, they might do things differently. People running plants aren’t interested in technology for technology’s sake. They view technology as nothing more than a tool, and need to know that the technology will help them achieve their goals without getting in the way of smooth, productive plant operation. In the absence of demonstrably better solutions, plant managers want to stick with what they know will work.

“Control system designers need to put themselves in their customers’ shoes, and analyze, from a plant’s perspective, whether a new piece of technology will add value. For example, if a fieldbus instrument designer was to follow the product from the factory to the customer’s plant and observe the calibration issues that the customer has, then the designer would do a better job of providing calibration support for future products. Factory calibration doesn’t always hold up, and things change at the installation site from when a system is initially specified. You need the capability of evaluating the instrument in the field and recalibrating it.”

Piper, of Invensys, says it really doesn’t matter which fieldbus you choose. “There are two essential functions of fieldbus,” he explains. “First, of course, is communication of measurement and actuator data for automatic, digital control of the plant, which provides significantly improved accuracy over conventional analog technologies. Second is the integration of digital instruments with the computer-based human interfaces that enable one-on-one interaction with these devices. The future of fieldbus isn’t so much in the physical media, or even the communication protocol, but in the functionality of new plant automation applications and their coupling to functionality within the field device. The physical layer is simply a means to that end.”

Based on what we’ve heard so far, it seems that HART, Profibus, Foundation fieldbus and DeviceNet are being used far and wide in the process industries with reasonably good success.

Not all instrumentation is fieldbus-compatible, however, and so vendors are feeling the pressure to convert their HART-based and other standard instrumentation to fieldbus. With many major, new projects going to fieldbus architectures, these vendors have to comply with fieldbus or lose the business. Moore Industries, for example, acquired a line of Foundation fieldbus and Profibus PA device couplers and power supplies from U.K.-based Hawke International, so it could expand its interface solutions for new and old projects alike. This allows Moore to offer fieldbus instrumentation along with fieldbus power supplies and device couplers for new Foundation fieldbus and Profibus projects.

Likewise, Softing recently announced a small Fieldbus Kit board that converts HART-based devices to Foundation fieldbus and Profibus PA. Fieldbus issues that remain unresolved are a universal, wireless, fielkdbus standard, the ongoing EDDL versus FDT debate, and fieldbus safety systems. As you might expect, the various standards committees are waffling, as major vendors try to force their particular technology into each standard. Still, progress is being made.

While they waffle, at least two 800-lb gorillas are lurking in the weeds, threatening to upset the fieldbus apple cart—Ethernet and wireless.

"Ethernet and Nothing Else"
That was the banner over a giant Automation IT booth at Hannover Fair, featuring exhibits from a host of companies, including Cisco, GE Fanuc, SAP, Pepperl+Fuchs, Harting, Sick, OSISoft, Fluke, and two dozen others, all linked together in an Ethernet network. Their premise was that Ethernet could link an entire enterprise, from IT to factory automation.

Although I didn’t see an example, booth literature claimed, “Line topologies such as the common fieldbus guarantee minimal effort and simple expandability.” That implies Automation IT is right outside the fieldbus door, and soon will be knocking to get in. Automation IT also claims it “provides direct, real-time access to all data in any application from any core process.” Knock, knock.

GE Fanuc, one of the Automation IT exhibitors, is a believer in Ethernet for fieldbus applications. “GE Fanuc sees DeviceNet fading and Profibus flattening out,” says Bill Black, GE Fanuc’s controllers product manager. “Ethernet has the highest potential for growth. We’re seeing more requirements to support multiple protocols such as Modbus TCP, EtherNet/IP and Profinet. The advantage of Ethernet is the relatively low cost of installation versus the high cost of specialty connectors and cables for Profibus and DeviceNet.”