EDDL and FDT Both Claim Gains

Two fieldbus communications technologies—Electronic Device Description Language (EDDL) and Field Device Tool/Device Type Managers (FDT/DTMs)—claim increased supplier adoption and user benefits at the recent ISA Expo.

“Enhanced” Electronic Device Description Language (EDDL) appears to be gaining momentum in the process control community, with the unveiling of a multi-vendor demonstration of EDDL enhancements at last month’s ISA Expo, held in Chicago. Located in the Fieldbus Foundation’s booth, the EDDL demonstration showed how automation suppliers, including Emerson Process Management, Endress+Hauser, Siemens and Smar, are implementing enhanced Electronic Device Description (EDD) features in their host systems and field devices.

Also at ISA Expo, the FDT Group made several key announcements, including its coalescence from the FDT Joint Interest Group, founded in early 2003, into a formal organization—The FDT Group AISBL—and the creation of a board of directors of executives from ABB, Endress+Hauser, Invensys, Metso Automation, Omron, Rockwell Automation, Schneider Electric and Yokogawa. Included in the initial 39 automation supplier and end-user member companies are Honeywell Process Solutions, Saudi Aramco and Shell Global Solutions.

Wide support

EDDL is a programming language that uses Device Descriptions (DDs) to describe attributes of field devices, such as data types, function blocks, default values and permitted ranges. The Device Description Language (DDL) is deployed in 15 million to 20 million field devices globally, and is supported by fieldbus networks including Hart, Foundation Fieldbus and Profibus. The EDDL specification was adopted by the International Electrotechnical Commission as IEC 61804-2 and is endorsed by the three leading process fieldbus organizations, including Fieldbus Foundation (FF), Hart Communication Foundation (HCF) and the Profibus Nutzerorganisation (PNO).

Enhancements to the EDDL specification have been approved by the three process fieldbus organizations and will be included in a new Part 3 revision to the IEC 61804 specification. The enhancements standardize the presentation of intelligent device information—such as waveforms, valve signatures and historic data—and improve data visualization and display capabilities for the automation system user.

The Field Device Tool specification—now known simply as FDT—was originally conceived by a group of European companies, led by automation conglomerate ABB, in the late 1990s as a way to standardize the interface between intelligent field devices and host systems, regardless of device vendor or fieldbus protocol. Device manufacturers include an FDT-compliant piece of software in their devices, called a Device Type Manager (DTM). This is used by an FDT-compliant frame application in the host to communicate with devices across different protocols.

Says Scott Bump, member of the FDT Group executive committee and director of fieldbus technology at Invensys Process Systems, “The great majority of large, global automation companies now belong to the FDT Group and we now have the critical mass to bring this important interoperability standard into the mainstream.”

Competitive or complementary?

The FDT Group is making a strong case for the complementary relationship between the FDT and enhanced EDDL technologies. According to a recent white paper from the group, “FDT simply defines the interfaces in an open, standardized way. DD files are still necessary to describe the devices to the system for system configuration. If the application is simple and can be accomplished with EDDL, this is a reasonable choice…If more advanced features…are needed, a language supporting those features must be selected.”

In late October, ABB released a positioning statement that states, “ABB understands [customer-owners’] high expectations for interoperability and integration of automation systems and intelligent field devices. While progress has been made, their expectations have not been met by any of the current fieldbus standards…ABB uses EDDL technologies together with these technologies (Hart, Profibus, Foundation Fieldbus) in its systems to integrate intelligent field devices. ABB uses FDT/DTM technology to integrate more sophisticated device applications,” citing examples that include valve diagnostics, radar level measurement and multivariable transmitters.

Expressing a different view is Rich Timoney, president and chief executive officer of the Fieldbus Foundation. “It’s true in the early days, DDL did not support graphic files and some other advanced functions. The new enhancements to EDDL include the graphic visualization in a protocol-independent device language.” Referencing the fact that DTMs are built on Microsoft Windows COM/DCOM (for component object model/distributed COM) technology, Timoney notes, “Introducing plug-in variables based on specific operating systems does not lead you to interoperability.”


It is the position of Emerson Process Management, as expressed by its president, John Berra, at the recent Emerson Global Users Exchange, that the enhanced EDDL standard satisfies requirements for intelligent device to host interface, and that the FDT/DTM technology is superfluous. Berra stated that the introduction of fieldbus products with EDDL enhancements “will end all the FDT/DTM nonsense that is out there.”

The enhanced EDDL specification is endorsed and supported by the OPC Foundation for use with the new OPC Unified Architecture specification. Says Timoney, “Why do I need Active X protocols that are language and version specific? EDDL with OPC UA provides a common architecture and interoperable environment.”

The automation industry will ultimately decide whether the FDT and EDDL technologies are competitive or complementary, as suppliers cast their votes with product introductions and end-users vote with their purchase orders. Certainly, there will be many more interesting developments, as evidenced by the announcement at the ISA Expo that Invensys will use the Hart Smart Device Configurator (SDC-625) technology to enable its process automation systems for enhanced EDDL. Invensys’ Bump calls this a “major alignment of FDT/DTM with EDDL, which will allow Hart devices to be fully integrated with the FDT/DTM architecture.”

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