This article was printed in CONTROL's October 2009 edition.
By Jim Montague, Executive Editor
Don't get too comfy. Sure, most digital fieldbus protocols are well beyond their awkward childhood and teenage years, and they're maturing into responsible young adults who are able to cooperate and interact with each other. Their many parents must be justifiably relieved and proud.
However, some new and ominous challenges remain, and our grown-up fieldbuses already are beginning to take on some challenging and unusual roles and tasks, such as safety instrumented functions (SIFs) that will allow them to serve in safety instrumented systems (SISs) or anyone of several wireless networking methods.
For instance, Ethernet-based protocols, wireless and even Internet-based networking are continuing their march down from the enterprise and larger consumer realms, and onto the plant floor and out into the field. Several observers say this push will force fieldbuses into sub-networks for production operations and process applications, while Ethernet flavors run above to reach higher-level asset management systems.
Others speculate that the dual progression from point-to-point hardwiring to twisted-pair to wireless and from highly centralized control to powerful distributed intelligence will make traditional control rooms obsolete. If all the smarts are in a super-smart network gateway in the field, why go back to a control room? This evolution may be logical, if not inevitable, but it also raises a question—will some of the useful potential of fieldbuses be wasted if they just serve as segregated commodities?
However, the good news is that most of the fieldbuses have been coordinating their efforts around electronic device description language (EDDL) for several years. The original partners included the Fieldbus Foundation (www.fieldbus.org), Profibus Nutzerorganisation (PNO, www.profibus.com) and HART Communication Foundation (www.hartcomm.org) with assistance from the OPC Foundation (www.opcfoundation.org), and they formed the EDDL Cooperation Team (ECT, www.eddlcoopteam.org). More recently, ECT has been working to welcome in new capabilities provided by the field device tool/device type manager (FDT/DTM) protocol and its FDT Group (www.fdtgroup.org), again with matchmaking from OPC and its OPC-UA technology method. This latest effort is known as the Field Device Integration (FDI) group, and its team members are drafting specifications now.
So, while complete plug-and-play interoperability may not have arrived yet, many persistent and crippling protocol translation problems have gone away or are vanishing, often with added help from improved linking devices. In general, fieldbuses have been getting a lot easier to use.
Steady 'Overnight' Success
Despite their recent gains and cooperation, digital fieldbuses have traveled a long and winding 10 to 15 year path to acceptance and adoption. Their developers and advocates have demonstrated plenty of patience in slowly chipping away at reluctant end users to get them to improve or replace old networking technologies. Fortunately, they've also had help from some enlightened end users hungry to gain the labor and material savings, otherwise-unobtainable signals and data, and operating efficiencies that fieldbuses can deliver. And, after struggling for a decade or two, some fieldbuses are breaking through to some long-awaited "overnight" successes in many major process applications.
"We've been using digital protocols for ‘smart devices' for many years. The earliest installations used vendor proprietary protocols, such as Honeywell's DE and Foxboro's Foxcom, which were installed in the early 1990s," says John Kinsley, of Saudi Aramco's (www.saudiaramco.com) Process and Controls Systems department. "We started piloting Foundation fieldbus (FF) technology in 2000. The initial field trials were limited to monitoring only segments typically in utilities areas or non-critical processes. Our first plant-wide installation was commissioned in 2004. Based on this experience and other pilot plants, we standardized on FF for process control applications and all new facilities in 2005."
Kinsley reports that, while FF's basic architecture hasn't changed much in the past four years, its adoption and use are growing rapidly. "Our installation base and experience level with FF technology has grown considerably. Since 2005, we've installed FF at seven grass-roots facilities with over 35,000 FF devices. The percentage of FF devices versus total I/O continues to increase as more devices are introduced to the market. On some of our earlier projects, the percentage of FF I/O versus conventional was approximately 25%. This number is closer to 40% on more recent projects. We've also increased the number of devices per segment as our confidence in the technology has grown."
Of course, FF isn't Saudi Aramco's only network. Kinsley adds that his company uses proprietary fieldbuses for MOV networks, gas chromatographs and tank gauging. "We're also at the early stages of adopting the IEC 61850 standard for substation automation," he says. "We have pilot installations in operation, but are still evaluating the technology. One of the critical components in the adoption of a new technology is to ensure there are sufficient numbers of suppliers for the end devices. We're in the process now of reviewing supplier capabilities before moving towards a wider adoption of IEC 61850. Also, we typically don't have a mixture of different fieldbuses in one facility. However, where we do, the data are interfaced to a central DCS that provides communication between the busses."