But that’s where the similarity ends. Each technology comes with its own history, its own place in the world of standards and its own manner of reading and displaying device intelligence. Although they are different in their approach to device intelligence, the two technologies do not compete the way Beta and VHS competed for the videotape standard. They are more like 45s and 33s in the world of vinyl recordings—they are different approaches that often live side-by-side within the same system.

EDDL and FDT grew in slightly different automation worlds. “EDDL and FDT have traditionally served in different markets with respect to device configuration, diagnostics and runtime operation,” says Thomas Burke, executive director, at the OPC Foundation, in Scottsdale, Ariz., which oversees the OPC open communication standard. “EDDL was really targeted toward the process industry, and FDT was targeted toward discrete.”

Both technologies attempt the same function—communication with field devices. Yet they are fundamentally different. According to a study by ARC Advisory Group Inc., in Dedham, Mass., EDDL and FDT are different technologies aimed at providing easy plug-and-play access to information in smart field devices. EDDL is a text-based language used to describe the communication attributes of a smart field device. It has been in use for more than a decade, and is governed by the International Electrotechnical Commission’s IEC 61804-3 standard. FDT is a Windows component object model (COM)-based technology. It is a universal field device communication interface that allows access to data for higher-level applications, and can be used in many industries beyond process control. FDT approvals for standards are still pending.

Complement or compete?

For the past few years, many have seen EDDL and FDT as competing technologies. Yet a growing number of vendors have declared neutrality on the matter of whether they prefer EDDL or FDT. Automation vendors are beginning to view the two technologies as complementary.

“Do the two technologies work well together? If you study the specs and study how systems are designed, there is potential for conflict,” says John Yingst, product manager at vendor Honeywell Process Solutions, in Phoenix. “For example, if the FF (Foundation Fieldbus) Link Active Schedule (LAS) is created using DD or EDDL information, the control system configuration tool knows all this information and should be the only means to change it. A DTM running via a co-resident FDT tool could inadvertently change some of that information without the system’s knowledge.”

Yingst notes that problems could be averted by designing in safeguards such as filtering to insure the integrity of the system-configured LAS information. “In practice, vendors have successfully allowed both technologies to coexist,” says Yingst.

Some vendors believe the use of both technologies will eventually become widespread. “In a year of two, all of the vendors will support both EDDL and FDT,” says Scott Bump, director of fieldbus development at Plano, Texas-based vendor Invensys Process Systems. Bump is also on the executive committees for both the Fieldbus Foundation and FDT. “These technologies complement each other extremely well with little overlap.”

Yet other vendors believe the two technologies will not blend. “I’m not seeing them used together. They’re totally different,” says Moin Shaikh, marketing manager for networking technology at vendor Siemens Energy & Automation Inc., in Alpharetta, Ga. “The tools they are based on are completely different. So end-users usually stick with one. There is a clear dividing line between those who use EDDL and those who use FDT.”

Capitulation

More and more vendors have decided to step out of the controversy and simply support the technology preferred by their clients. “We support both technologies and they are complementary,” says Amit Ajmeri, consultant for fieldbus technology and asset management solutions at automation supplier Yokogawa Corp. of America, in Newnan, Ga. “The basic difference between EDDL and FDT is the way the information is presented to the end-user. Some end-users prefer EDDL, some prefer FDT, so we support both technologies.”

The trend among control vendors is to adopt both EDDL and FDT. “As for using both, it depends on the host system. In the process automation world, the end-users select the control system first, then the field devices. If it’s a straightforward EDDL, we don’t encounter any issues,” says Marty Zielinski, director of Hart and fieldbus technology at Emerson Process Management, an Austin, Texas-based automation supplier. “If the host system emphasizes FDT/DTM, we encounter issues. The biggest problem is when the customer has a host system and upgrades it, and all of the sudden, the end-users discover FDT technology. That’s problematic.” ...