The One Network

Our Intrepid ‘On the Bus’ Columnist Joins the Search for the Single Network Standard for Digitally Integrated Transmitters

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By John Rezabek

Our sister publication, Chemical Processing, sent me an alert the other day about a new feature for Micro Motion Coriolis transmitters from Emerson Process Management. Its latest offering now natively supports DeviceNet and Profibus DP, and already had supported HART 4-20 mA, Modbus and wireless.

If the mythical Tower of Babel had implemented an industrial network, I think 21st-century controls professionals could have provided the design and troubleshooting. That’s because it appears that our supplier community is gearing up for a diverse spectrum of interconnection options, instead of the global standard once envisioned for IEC 61158.

In the late 1980s and early 1990s, end users were eager to connect dissimilar systems—DEC Vax-based historians, tank-gauging systems, analyzer networks or minicomputers running model predictive controls—to their DCSs. Anyone remember the ISA show with the dinosaurs wearing CRT glasses? Microprocessor-based instruments, or “smart” transmitters and valve positioners, were introduced at the same time. Modbus was the de facto standard, as well as the path by which DCS vendors proclaimed their systems to be “open.” We were already imagining what could be gained by connecting the microprocessors in field devices directly to the DCS, when Honeywell delivered DE. End users and Honeywell’s competitors agreed that a proprietary solution for a digital field network was not in anyone’s best interest, and work on a digital replacement for 4-20 mA began.

Twenty-five years after the first digitally integrated transmitters were introduced, there’s still debate as to whether any clear standard ever emerged. The Fieldbus Foundation (FF) says it has “the” standard. Meanwhile, the Profibus Trade Organization (PTO, us.profibus.com) says it won the “Fieldbus Wars,” citing staggering numbers of installed nodes. And some say the smart money is on Ethernet because its ubiquity may overtake all the rest.

Laggards, Late Adopters and Installed-Base Inertia

“WirelessHART and ISA100.11a appear to continue their non-interoperable ‘competition’ for the wireless standard. It appears the vendors haven’t learned this lesson from their previous wars and need to learn it again,” says Bill Hodson of Hodson Consulting LLC in Philadelphia, who is working on a Foundation fieldbus high-speed ethernet (HSE) gateway for Wireless HART. User enthusiasm for fieldbus in the 1990s was similar to what we’re experiencing with wireless today. And like today, deep divisions, split loyalties and competitors refusing to concede any ground to one another, delayed any standard for years.

Ten years after the first pioneers installed early incarnations of fieldbus on the North Slope of Alaska and elsewhere, the main players—Foundation fieldbus, Profibus and HART (implemented as a device digital integration strategy)—are still in the minority. How is it that a technology that was so pined for in the 1990s isn’t a no-brainer today?

We Don’t Need No Stinkin’ Diagnostics

Fortunately, while the Fieldbus Wars were raging, users didn’t hold still. A significant number continued with DCS and field instrument upgrades when the capital was available, using the technology of the day—4-20 mA and proprietary protocols like Honeywell’s DE. Unfortunately, the systems installed weren’t well-equipped for integrating the upcoming fieldbus options, including HART.

In many sophisticated plants, the value of control systems had visibility well into the executive ranks. These plants staffed up and maintained organizations needed to keep the plant running optimally. Advanced control and optimization strategies rely on measurements being timely and valid, and control valves going to the requested position.

When management understands the value of its control system, resources tend to flow as needed. The other day at our International Specialty Products’ plant, we had a chromatograph service tech whose friend just landed a great-paying job in a Gulf Coast refinery. The plant manager there had decreed, “Analyzers will have 98% or better reliability,” and they hired the people they needed to get it done with the kit they had on the ground. Once in place, an experienced staff will excel with what it has—and for many sophisticated users it isn’t fieldbus.

Before any of us had a digitally integrated smart valve, we had some great diagnostics generated by the organization itself. Experienced board operators possess lot of good diagnostics embodied in the phrase, “I don’t believe this transmitter.” And, in less-dysfunctional organizations, they communicate as much to the instrument department. When you add to this a staff of advanced control and optimization professionals whose duties include daily scrutiny of the effectiveness of their applications, your ability to detect and even predict deficiencies in the measurement and control infrastructure becomes fairly comprehensive.

We’ve also had at our disposal diagnostic tools in the form of tuners and historian analysis tools. ExperTune’s Plant Triage and ControlSoft's Intune+ can analyze standard analog 4-20 mA signals from old-school DCSs and identify many issues with measurements, positioners and controller tuning. Gensym-based expert systems like Nexus Solutions can offer even more standardized and customized diagnostics based entirely on “olde-tyme” analog signals. Rudimentary rules such as, “If this pump is running FT-101, should show no flow,” or “If the valve is 30% open, the flow should be <blank>” can be implemented without enormous effort.

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