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. Thats 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 systemsDEC Vax-based historians, tank-gauging systems, analyzer networks or minicomputers running model predictive controlsto 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 Honeywells competitors agreed that a proprietary solution for a digital field network was not in anyones best interest, and work on a digital replacement for 4-20 mA began.
Twenty-five years after the first digitally integrated transmitters were introduced, theres 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 havent 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 were 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 playersFoundation 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 isnt a no-brainer today?
We Dont Need No Stinkin Diagnostics
Fortunately, while the Fieldbus Wars were raging, users didnt hold still. A significant number continued with DCS and field instrument upgrades when the capital was available, using the technology of the day4-20 mA and proprietary protocols like Honeywells DE. Unfortunately, the systems installed werent 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 hasand for many sophisticated users it isnt 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 dont 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.
Weve also had at our disposal diagnostic tools in the form of tuners and historian analysis tools. ExperTunes 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.