Over the past few years the HART Communication Foundation and other organizations have worked in cooperation with automation system and device suppliers to produce enhancements to the Electronic Device Description Language (EDDL, IEC 61804-2). Phase One of the update process is now complete, specifications for the new enhanced EDDL have been submitted to the IEC for approval, and manufacturers have begun to implement the new EDDL.
So, the question from users is: “Why should I care?” What does all this mean? What are EDDL, DDs or EDDs anyway?”
The IEC Electronic Device Description Language specification refers to an all-encompassing specification with subsets dedicated to the specific protocols using the specification (HART, FF and PROFIBUS). Not all of the specification is implemented by each protocol, only the appropriate subset.
Using Electronic Device Description Language, a DD or EDD is written and tokenized (similar to a compiling process) into a protocol specified binary encoded file, not an XML file. This encoded binary file is used by a host application to learn what features reside in a device. Because the DD is not an executable file it is unaffected by an operating system and will work on handhelds, PC-based programs, or asset management applications. “One DD to work everywhere.”
The new enhancements correct a trend where DD-enabled host systems were getting away from the original intent of the language--to use one file per device to describe the resident features. Host system suppliers began to require device manufacturers to produce additional files or host specific DDs and to require additional testing of devices in order to use their DD.
This meant that a device manufacturer might not support the host a user was implementing, keeping users guessing as to what was the correct DD for the device/host combination being used.
The new enhanced EDDL specification promises to reduce the complexity and streamline the process for everyone involved. Host suppliers have agreed that no additional files or host specific DDs will be required which will improve quality assurance and interoperability of a device manufacturer’s DD across all host systems.
Users will need only one DD for the version of the device they have installed and can be assured that if they get the DD from the HCF DD Library it is going work with their host.
This is exciting news, but even more so is that EDDL provides new interface options. HART users will continue to see the original tree menu structure they have become accustomed to while allowing device manufacturers to describe new graphic “Windows like” menu structures making the setup of a device easier to understand. See Image 1.
Image 1 - Menu Comparison
In addition, the enhancements allow a device developer to describe not only the device features, but also soft-tools that will allow the user and host to better analyze the digital information coming from the device. The tools include new calculation capabilities, support for images, the presentation of tabular data, real-time data logging and the storing and display of historical information on each device.
And, real-time data logging of information (signal strength versus level, temperature and flow variations over time), is just the beginning. See Image 2.
The EDDL enhancements also allow device manufacturers to present historical data against current readings. This allows users to track things like valve wear using valve signatures or to resolve echo curves for radar level gauges. The host stores historical data in a file defined by the DD, , and then the data is presented to the user on an x-y graph allowing a comparison of the original data to the new data. With this information users can decide when to do preventive maintenance on a device based on actual data versus cycle time or event.
Enhancements to the technology allow HART users to bridge the gap between traditional analog devices and smart digital devices using intelligent field communications. This bridging provides a continuous forward migration path with no user investment loss. This migration path is vital to cost-conscious companies that work with continuous processes.
Because HART devices support two simultaneous communication channels on the same wire (4-20mA “current loop” analog and HART digital), HART Communication is the logical migration path for the millions of legacy systems still in use. All HART-enabled instruments produce or accept a 4-20mA analog control signal compatible with systems produced over the past 30 years. No loss of investment occurs when upgrading using the HART / EDDL path.
The expected growth rate for HART Communication coupled with the recent enhancements to the Electronic Device Description Language assures users that they will continue to maximize their investment in HART technology for many years to come.
Finding a place to begin integration of HART data is the key to future improvements in process performance. When control systems use only the 4-20mA analog communication channel, an “information gap” exists. Continuous real-time HART communication closes that information gap by providing a two-way exchange of process information.
Integrating HART Communication with plant systems is easy and cost-effective. Get started today. Close the information gap and “See What You Can Do” when you use the “Power of HART”.
Want to know more about how to use HART technology? Join the HART Users Group! And watch for upcoming HART Connection articles that will provide information on applying HART technology, application notes to help you implement new HART strategies and what to expect from a HART-enabled device or host system. For more information, contact the HART Communication Foundation or go to http://www.hartcomm.org.