Emerson works with standards groups expand DDL technology

Austin, TX— Emerson Process Management is collaborating with global standards groups to enhance Device Description Language (DDL) technology. Emerson reports that, after carefully considering user needs, it believes enhanced DDL offers a better solution than a proposed alterna-tive called Field Device Tool/Device Type Manager (FDT/DTM).

Emerson adds that efficiency in ownership of process automation requires that users be able to cost-effectively add, upgrade, and integrate instruments, equipment and systems of choice. Open, interoperable, standards-based DDL is a proven global technology that meets these needs in thou-sands of installations.

DDL provides underlying technology used by host suppliers to design robust 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.

The FDT Joint Interest Group (FDT JIG) is performing FDT/DTM’s development as an alternative with goals described as similar to the DDL collaboration. Emerson says, while the goals are unarguable, its review of the FDT/DTM concept prompted concerns about important short-comings for users based on technical issues. In Emerson’s judgment, DDL technology surpasses the FDT/DTM technology in meeting end-users’ needs, including freedom of choice of instruments, equipment and systems; clarity and ease of use of HMI design and displays; streamlined integration of field devices; and efficient system upgrades.

Emerson adds that DDL technology is proven because it’s used in the millions of HART, Profibus DP and FOUNDATION fieldbus devices installed by users. DDL provides underlying technology for effective HMI interface to this large and rapidly growing installed base. FDT/DTM is missing provisions for these users. As a result, Emerson is focusing its resources on enhancing and standardizing DDL, and is collaborating with standards organization members to speed enhancement of the established technology toward the goal of an ever-strengthening HMI interface.

FDT’s abilities FDT JIG responds that Emerson’s statement that DDLs are able to address what end-users want in HMIs is true, but because DDLs are structured text files, they don’t lend themselves to the richness of capabilities that are required for complex measurement devices, such as valves, positioners and radar level transmitters, which require a greater engineering commissioning effort.

“The good news is FDT welcomes what Emerson and the DDL’s enhancement group are do-ing to improve DDL technology because it becomes seed stock for converting DDLs into DTMs. This is because DDLs can’t address more complex field devices, and so FDT is needed to pick up where DDLs leave off,” says Nick Zucchero, Invensys Process Systems’ systems technology director and an FDT JIG steering committee member. “Emerson shouldn’t sell FDT short because we really can help extend the benefits provided by DDLs and extend that technology for complex equipment.”

Enhancing DDL Emerson is supporting members of the HART Communication Foundation, Fieldbus Foundation, and Profibus International in their efforts to expand visualization tools within DDL technology. Being developed within the context of the existing IEC 61804-2 DDL draft international standard, enhancements to DDL streamline the ability of host suppliers to deliver one engineering interface capable of configuring, operating, and maintaining any smart field device, independent of vendor and communications protocol. IEC 61804-2 has been approved and will be circulated in January 2004 for a two-month ballot as an international standard.

Emerson presently offers HMIs as one interface that supports HART, Modbus, DeviceNet, FOUNDATION fieldbus, Profibus DP, Profibus PA and ASi Bus, as well as a wide variety of legacy communications. To participate in collaborative DDL efforts, Emerson reports that it’s continuing its dedication to standards, and is strengthening FOUNDATION fieldbus, while enhancing single-interface availability across the industry.

FDT/DTM alternative to DDL Emerson adds that FDT JIG has shaped a technology with an FDT that is a “software receptacle” into which a DTM is “inserted.” The FDT provides interfaces to the software architecture of the host system, and so that FDT it becomes an integral part of the host system. The FDT provides access to underlying services, such as display, keyboard, database, and other generic host features. It also provides access to any digital communication interfaces the host system might possess.

The FDT specification requires implementation to be accomplished with a Microsoft Windows Operating System (OS), and is built on Microsoft’s Component Object Model (COM) and Distributed Component Object Model (DCOM) technology. Because COM/DCOM doesn’t support real-time data exchange, these technologies have been extended to accommodate this requirement.

FDT is intended to provide interface to the HART, FOUNDATION fieldbus and/or Profibus communication drivers, if they are present in the host system. Emerson says that FDT JIG only supports HART and Profibus at present.

Emerson explains that a DTM is software supplied by the field device manufacturer. It is installed as a component of the software architecture. A DTM is “plugged into” the FDT, and uses Microsoft Active X to access services provided by the FDT. By using available FDT ser-vices, the DTM provides all access to the field device.

Likewise, all of the information that a device manufacturer wants to make available is programmed into the DTM. This includes all real-time data, alarms, events, configuration information, screen displays, multilingual help screens, device specific documentation, parameter validity check, generation of dependent variables, diagnostic functions and the device calibration sequence. One DTM can support more than one field device, but this increases its programming complexity.

HMI with FDT/DTM In the proposed FDT/DTM technology, software for implementing HMI visualization is the responsibility of the field device suppliers, according to Emerson. HMI screen images served up with data from the devices have a different look and feel from each field device supplier. DDL insures a consistent look and feel on a given host system because the host implements a single interpretation for all device description files, independent of vendor. FDT JIG reports that it has a style guide, and that it will test for common look and feel, without sacrificing ability.

Upgrade management, revision control While DDL is designed for interoperability, FDT/DTM requires custom drivers, i.e. its DTMs), which tightly integrate the field device software with a host operating system. This executable software must be maintained by the field device manufacturer, and integrated by the host system supplier.

FDT/DTM technology’s operating system dependence and its tight integration of software lead to more challenging upgrades. For example, there are significant differences between Microsoft Win 95, 98, Me, NT, 2000, and XP. More significant changes are coming in the Microsoft Longhorn release that has significant graphical user interface (GUI) changes.

Emerson says it’s unlikely that the DTMs of all vendors’ field devices would work correctly when upgraded with host system software, and that DTMs of all the vendors’ field devices would work correctly in the new Windows OS. Emerson says an existing DTM must be integrated in the host when new features or functionality are added, or when the OS is upgraded. It’s not clear who is responsible for ensuring continued compatibility between the DTM and the host system FDT. It will likely be a combination of the device manufacturer, the host system supplier, and the end-user. Their roles are interdependent and will require expensive, often time-consuming negotiation. A similar integration process for a new proprietary software driver must occur when a field device is revised or upgraded.

Emerson concludes that it’s unlikely that installed DTMs can keep pace with enhancements, and even more unlikely that they can survive an upgrade. This will likely force host system suppliers to restrict the number of different vendors’ field devices. Otherwise, revision control would become unmanageable.

Control Engineering Daily News DeskJim Montague, news editorjmontague@reedbusiness.com

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