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.”
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.”
In a growing number of cases, plants are using a combination of EDDL and FDT. “Many plants are using FDT in conjunction with EDDL,” says Achim Laubenstein, manager of fieldbus standardization at vendor ABB Inc., in Norwalk, Conn. He notes that there are two cases for this. First, the basic integration is done with EDDL, but additional advanced diagnosis functionality is provided by the device vendor at FDT/DTM, which runs in a FDT frame application. In the second case, several device vendors do not provide DTMs for their simple to medium-complex devices. In this instance, those EDDs are run in an EDD interpreter DTM.
“In both of these cases, FDT and EDDL complement each other,” says Laubenstein. He also notes that they work very well together. “An FDT-based system can always integrate EDDs through so-called ‘interpreter DTMs,’ ” Laubenstein observes. “By this, the tremendous installed base of Hart devices and their DDs can be covered in a very efficient way.”
Blend the technologies
Because both EDDL and FDT have their adherents, and both are clearly here for the long run, the industry has started an initiative to integrate the two technologies. “Many end-users say they are not comfortable with these two technologies in tandem,” says Flavio Tolfo, managing director of the FDT Group, in Belgium. “You can use EDDL-based device description, and use some interfaces or interpreters and make them compatible with DTM.” Tolfo describes that informal integration as “field device integration light.” It’s not full integration, and yet the two technologies are working together.
As part of an industry effort to integrate EDDL and FDT, a number of groups created FDI, the field device integration initiative. “There is a project among all the major suppliers to bring together EDDL and FDT technology into a single technology that will be compatible with both technologies,” says Tolfo. “That’s field device integration, or FDI.”
The FDI initiative began in 2003. “FDI is made up of five organizations. Initially it was the three fieldbus organizations, Fieldbus Foundation, Hart Communication Foundation and Profibus,” says Shannon Foos, segment manager for process network connectivity and asset management at supplier Rockwell Automation Inc., in Milwaukee. Foos is also the North American marketing director at FDT Group. “Part of the charter for the FDI is the need for a unified method to traverse the software layer of the control system, so they invited the OPC Foundation to aid them in supporting the integration. The FDT Group was also invited to join.”
One piece of glue that may be a factor in integrating EDDL and FDT is OPC. “I’ve been to briefings of the FDI effort. They’re trying to come up with a more cohesive spec that encompasses the two technologies,” says Yingst, of Honeywell. He notes that technology from the OPC Foundation may be a key element in integrating EDDL and FDT. “OPC UA (Unified Architecture) is a way to put some standards around the process of getting data from devices,” says Yingst. “We have a nice OPC engine in our system, and it provides a nifty way of getting data out of fieldbus devices.”
Going forward, the industry may find the battle over EDDL and FDT simmers down to a vendor-wide adoption of both technologies, perhaps in an integrated form. “No one has a magic crystal ball, but a few things are known about the future of these technologies. First, DD technology is definitely here to stay,” says Yingst. “The installed base for Hart and FF devices alone is insurmountable, and despite a glitch here and there, the technology is rock solid.” He also notes that FDT/DTM is here to stay. “FDT/DTM is definitely gaining in popularity. It is quickly becoming the open standard of choice for advanced diagnostics, especially among valve actuator vendors.”
As a way of dealing with two standards that are likely to continue with strength, Yingst has hopes for FDI. “The FDI project is a way to help deal with what seems like too many standards,” says Yingst. “The goal of FDI is a common device integration technology compatible with both standards. It’s also targeted to include OPC UA to address the issue of a common standard for data access to field devices.”
With both EDDL and FDT/DTM well-established in their installed bases, the future for both technologies seems sound. For end-users, the future may be a matter of learning how to use the technologies side-by-side. Most end-users are not particular. They want the solution to work. FDI may be the answer to bringing these two different technologies into a seamless integration.
Related Sidebar - What is EDDL?
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Related Sidebar - What if FDT?
To read the article accompanying this story, go to www.automationworld.com/feature-5376.