The Fieldbus wars have plagued device manufacturers for years. Complying with HART, Profibus or Foundation Fieldbus meant writing various device descriptions, as each had its own slant on how it communicated the characteristics of an intelligent device back to the control system.
But about two years ago there was a truce. The HART Communication Foundation, the Fieldbus Foundation and the Profibus Nutzerorganisation banded together, each providing its own individual electronic device description language (EDDL) specification. Those various specs were to be unified within the International Electrotechnical Commission IEC 61804-2 standard. This collaboration was a huge moment in field device history, as it promised to remove from device makers the cumbersome task of writing multiple device drivers for each fieldbus protocol. For device developers, having a common language would lower engineering cost. For end users, it would mean a visually appealing interface that is uniform across different vendors' devices and digital control systems (DCS).
"It was a noble idea, and the miracle of all miracles is that they did it," says Dick Caro, CEO of CMC Associates (Acton, MA). IEC took device description attributes from HART, Foundation Fieldbus and Profibus, mixed and matched them and developed a single common language that is currently in draft form to become an international standard by the first quarter of 2006.
The three groups, along with the OPC Foundation, have agreed not only to comply with the standard, but to cooperate and contribute technology that allows the text-based file to be converted to easy-to-see graphics and charts that can be displayed on a screen by the process-oriented DCS. This aspect of the standard is referred to as "enhanced EDDL."
Major consortium-contributing DCS vendors including Emerson Process Management (St. Louis, MO), Siemens Energy & Automation Inc. (Alpharetta, GA) and Honeywell Process Solutions (Phoenix, AZ) are all planning to roll out enhanced EDDL-enabled asset management products over the next few months.
But does IEC 61804-2 signify peace and an end to the fieldbus wars? Not yet.
In the background looms another device description technology: Field Device Tools and Device Tool Management (FDT/DTM), introduced several years before the EDDL agreement. The idea -- which was spearheaded by ABB Ltd. (Zurich, Switzerland) -- was to develop a single set of attribute names that could be used independent of whatever communication bus was actually being employed, providing portability at the user layer. So, like EDDL, it offered device independence. And vendors like Rockwell Automation (Milwaukee, WI), Invensys Process Systems (Foxboro, MA) and Omron Corp. (Kyoto, Japan) lined up behind FDT/DTM, as did device manufacturers Endress+Hauser Group (Reinach, Switzerland), Pepperl+Fuchs GmbH (Mannheim, Germany) and SICK AG (Waldkirch, Germany).
Today, despite the fact that protocol-independent device interfaces exist, there are still two from which developers must choose. Big FDT/DTM backers, including ABB and Invensys, say the two technologies are complementary, but that doesn't negate the need for DCS and device vendors to choose to support one or the other or both.
So indeed, there's still a war, just not the fieldbus wars of past. Rather, it's a device description language battle that's brewing.
"It's the EDDL and FDT wars now," says Mike Bryant, executive director of the Profibus Trade Organization (PTO) in Scottsdale, AZ.
EDDL vs. FDT
In many ways, FDT overlaps what enhanced EDDL would do. FDT defines device-specific data, functions and business rules such as communication capabilities and human machine interface (HMI) structure. According to specification information, it can also work with HART, Profibus and Foundation Fieldbus and already has the graphical elements that enhanced EDDL promises. In fact, some industry observers say FDT offers a superior way of handling sophisticated field devices.
That's why some say the two technologies are complementary -- not competing. According to Scott Bump, director of fieldbus technology development at Invensys Process Systems, "EDDL is a description language that defines simple applications related to devices and is used largely to configure those devices. FDT is a Windows-based interface specification between device management software and asset management applications running in control systems." Invensys systems support EDDL-based fieldbus applications interfaced to the system using FDT, he notes.
However, therein lies the FDT drawback: It's operating system-dependent, tied very closely to Microsoft Corp.'s Windows-based technology. That means when a new version of Windows comes out everything has to be upgraded, says Ed Ladd, HART Communication Foundation's director of technology programs.
EDDL, on the other hand, is OS neutral. The way in which the EDDL specification is set up, 80% of the device descriptions are the same across HART, Profibus and Foundation Fieldbus, while the other 20% are technology-specific, say industry experts. Upgrading to enhanced EDDL, however, is very easy to do. "The device itself doesn't change," Ladd explains. "The manufacturer that builds a device can add as few as 20 to 30 lines of code [to support graphical views of enhanced EDDL] which is very little to incorporate the graphic functionality from a menu standpoint. So basically a user gets a new device description, but it doesn't stop them from using the old way."
Because FDT came on to the scene first, most of the device and control system vendors jumped on the bandwagon. Emerson -- which never committed to FDT -- is the only vendor that is 100 percent behind EDDL, primarily because "EDDL is a standard backed by the IEC," says John Berra, president of Emerson Process Management. FDT is not -- yet (see sidebar).
Emerson, a big supporter of HART and Foundation Fieldbus, this month will release a new version of its predictive maintenance software, AMS Suite Intelligent Device Manager, that includes support for enhanced EDDL. "It will have better visuals, more useful, colorful graphics and can be used with [more] devices," Berra says. "It's a logical step forward."
And in phase two, currently in the works, enhanced EDDL will be built into the OPC Unified Architecture (UA). OPC provides an interface at the system host level that bridges the gap between heterogeneous control devices, like programmable logic controllers (PLCs). Combining OPC and enhanced EDDL will provide a simpler way for users to access performance-based measurements and process data at the control and enterprise system level.
"EDDL will provide all of the descriptive data end users are saying they want," says Rich Timoney, CEO of the Fieldbus Foundation (Austin, TX). "Things like alarm management, client/server operations, HMIs...it will provide better access to a lot of the data end users use to operate the plant. They'll not only have the data but the visualizations like graphs and charts and historical trends that help fine-tune parameters in the process."
Playing Both Sides
Despite the constant wrangling between FDT and EDDL, most vendors like Invensys, Honeywell and Rockwell Automation are straddling both hemispheres.
For example, in October Honeywell announced it had joined the FDT Group, yet it also reaffirmed support for EDDL. According to a company spokesperson, "the company will support whatever its customers want." A source close to the company said an enhanced EDDL asset management product from Honeywell is almost ready for roll out.
Meanwhile, "FDT technology is complementary to DDL technology and holds promise in other areas, specifically around the support, configuration and diagnostics for more sophisticated subsystems, especially in the discrete and hybrid industries," says Paul Butler, Honeywell Process Solutions vice president of technology, in a statement, echoing statements made by Invensys officials. That means Honeywell, like Invensys, will have solutions that support both technologies.
Similarly, ABB released a statement in October to reinforce its support for both FDT and EDDL. "Recently, there have been negative public statements about FDT/DTM technology," said Mark Taft, ABB's senior vice president, systems marketing. "The authors of these statements want their audience to believe that FDT/DTM technology and EDD are competing, mutually exclusive technologies -- either you support EDD or you support FDT/DTM. This assertion is simply false," he stated.
The bottom line: While DCS vendors do have a choice of supporting FDT or enhanced EDDL (or both), device manufacturers don't. They must support both languages. "This puts a heavy burden on non-systems vendors like Endress+Hauser," says CMC Associates' Caro.
The good news for end users is that they'll feel no impact at all. "All of this is implementation detail," says Caro. Currently, there's a lot of vendor posturing. "But it's a behind-the-scenes war and end users don't really care...they just want the system to work."