A wish list satisfied
Improvements and extensions to the Device Description Language

EDDL technology is used by millions of installed field instruments and is thus a de facto standard for ensuring that information about intelligent field devices is available to operators, engineers, and maintenance technicians. The best news is that the EDD source file created for instrument number one works right alongside the EDD source file for instrument number 5 million — never once requiring an upgrade, revision, or patch.

When IEC 61804-2 Electronic Device Description Language (EDDL) was approved as an international standard in March 2004, EDD source files created using EDDL were already deployed in millions of process industry field devices. EDDL is a text-based language for describing the digital communication characteristics of intelligent field instrumentation and equipment parameters—device status, diagnostic data, and configuration details—in a way that is independent of the operating system (OS) and human-machine interface (HMI). Device Descriptor Language (DDL) technology first appeared in 1990 and has become a significant technology in many industries. The Hart Communication Protocol (Hart) began using DDL technology in 1992. EDDL is now being enhanced to extend the concept of interoperability to the HMI and diagnostic data.

Today, EDDL technologies form the engineering and operating foundation on which digital fieldbus protocols like Foundation, Hart and Profibus construct parametric and device descriptions. And, because EDDL is an open technology with the status of an international standard, it can be easily and effectively applied to any device and any fieldbus protocol. EDDL technology enables a host system manufacturer to create a single engineering environment that can support any device, from any supplier, using any communications protocol, without the need for custom software drivers for each device type. Key elements of EDDL technology are:
Operating system independence
EDD files do not contain specific operating system commands or instructions, so they remain transportable and independent of the operating system.
Consistency and uniformity
EDDL technology’s architecture supports multiple protocols within the same host application, and requires no custom tools to maintain a common look and feel.
Single engineering environment
EDDL enables a host system manufacturer to create a single engineering environment that can support any device, from any supplier, using any communications protocol, without the need for custom software drivers for each device type.
Revision control
Device revision is used to identify the revision level of a device. This enables manufacturers to improve an existing device’s implementation, such as adding support for additional parameters or enhanced diagnostics.
Testing and registration
Testing includes validating the syntax, dependencies and other protocol and language rules using toolkits, and registering the EDD binary file with the appropriate fieldbus organization.
International standard support
EDDL technology is an international standard approved by the International Electrotechnical Commission (IEC) and is available as standard number 61804-2. It also makes use of ISO standards for language and country codes.
Normally, process industry users are cautious about buying “technology hype”. What they usually demand is:
-freedom of choice in plant-floor instrumentation and equipment—valves, transmitters, motor starters and remote I/O— independent of the host.
-consistency in how plant-floor instrumentation and equipment is engineered,
-flexibility and efficiency in how plant-floor data is shared throughout the enterprise,
-ease of maintenance, and
-quantified proof that manufacturers have long-term commitments to expand and improve the underlying technology.
EDDL extensions
In February 2003, representatives of FF, HCF, and PNO met in a collaborative project to extend the capabilities of the IEC 61804-2 standard.
The scope of the co-operative project is to add robust organization and graphical visualization of device data, plus support for persistent data storage features, to IEC 61804-2. Sophisticated devices with hundreds of configuration, calibration, and diagnostic parameters, such as control valves, radar level gauges, and variable frequency drives, will benefit from the new user interface enhancements. Once implemented, the new extensions will
further unify the HMI environment. Using familiar dialog boxes, text, dynamic variables, pictures, charts, and archived data are presented to users in a consistent and familiar format. Graphs, such as control valve signatures, may incorporate pan/zoom functions so that they can be inspected in detail. Additionally, EDDL extensions support user interaction with device content, such as allowing filter values to be adjusted. By providing a standard, platform-independent means for displaying graphical information, device suppliers using EDDL technology can focus resources on increasing product features to better meet user requirements, confident that the solutions they develop will be delivered consistently across a variety of platforms and operating systems.
One EDDL extension requested by end-users is support for persistent data storage. This new feature allows device manufacturers to instruct the host application to store device or local data. This implementation method relieves the intelligent device manufacturer of having to learn the nuances of different host applications’
file systems; how data is stored is left up to the host application.
Persistent data storage enables a variety of new applications using EDDL technology. For example, valve diagnostic software developed using EDDL technology can archive valve signatures for later review by support personnel.
The benefit of IEC 61804-2’s neutrality is again revealed with the addition of the new EDDL extensions.
For example, an intelligent field instrumentation manufacturer who previously developed products for use on the FF protocol isn’t required to begin using the new EDDL Tokenizer, Viewer, and Services tools until its products begin using the new EDDL extensions.
In fact, for simple devices, EDD file developers may continue writing EDDL files in the same way they do today, using
either their existing tool or a new one.
For more complex devices, developers can use an existing EDD file as the
starting point in creating the extended EDD file. EDDL is being enhanced,
but it is maintaining backward compatibility with the millions of devices that
have been installed over the past ten years.
Because an extended EDD file contains additional field device information, PAS host systems must be updated with a new EDDL Host Services module. This is available to all PAS suppliers from the various fieldbus protocol organizations. More importantly, the Host Service Module provides backward compatibility for plant floor devices using older EDD files.