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Dueling Standards for Defining Devices On Fieldbus Networks

Apparently firing another round in the “fieldbus wars,” Emerson Process Management (www.emersonprocess.com) announced an initiative to enhance Device Description Language (DDL) technology to counter the rival Field Device Tool (FDT) specification.

According to Emerson, efficiency in ownership of process automation requires that users be able to cost-effectively add, upgrade and integrate instruments, equipment and systems of choice. Further, since DDL has been proven in current use, Emerson sees no need for another device specification. Rather an enhancement to the language is all that is needed, the company says.

DDL provides underlying technology for use by host suppliers to design human-machine interface (HMI) and automation interfaces, and enhancements being developed will add to this functionality. DDL-based field devices from all suppliers will interface identically to the various hosts. When host operating system changes are needed, the host suppliers have complete ability to make all upgrades; field device descriptions are unaffected.

FDT/DTM technology development has recently been undertaken by the FDT Joint Interest Group (FDT JIG) as an alternative, with goals that are similar to those stated by Emerson. (See Automation World, Jan. 2004, Net World, p. 46.) While the goals are unarguable, Emerson’s review of the FDT/DTM concept prompted concerns about important shortcomings for users based on technical issues.

Since DDL has been used for several years and employed in millions of HART, Profibus DP and Foundation Fieldbus devices, Emerson has decided to focus its resources on enhancement and standardization of DDL. To this end, it is collaborating with members of the HART Communication Foundation, the Fieldbus Foundation and Profibus International to speed this enhancement.

DDL is a text-based language for describing the characteristics of field devices used in device networks. Developed by the Fieldbus Foundation, it can be used on devices also based on HART and Profibus specifications. Based on Microsoft’s common object model (COM) and distributed common object model (DCOM), the announced goal of FDT was to be a universal device description language that is not tied to a specific fieldbus network.

Gary Mintchell

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