Comment

September 2009

System Integration

FDT + EDDL = FDI

Upon standardizing interfaces, the guarantee is the consistency of data, documentation, and configuration

By Nicholas Sheble

Device integration allows each instrument’s data presentation to be familiar and informative to the operator. No doubts, no searching, and no confusion are part of the man-machine information exchange.

Regardless of the model, the vendor, the age of the device, the communication protocol at work, or the complexity of the measurement, the output display will be consistent graphically and in content when successful device integration is at work.

With the advent of and commercial adoption of digital fieldbuses in the 1990s, two techniques of device integration came to the fore and are popular still—FDT and EDDL.

Field Device Technology (FDT) is traditionally associated with users and vendors of the discrete persuasion like ABB, Endress+Hauser, Invensys, Metso, and Siemens. However, not solely so. FDT is not a factory-automation-only technology.

To be sure, FDT is platform independent granting the freedom to choose best-in-breed instruments and maintenance tools without constraints of communication or platform compatibility.

One needs not replace existing installed devices. FDT technology incorporates existing device models.

FDT supports HART, Profibus, Foundation Fieldbus, DeviceNet, Interbus, AS-Interface, and ProfiNet. Importantly, FDT is an international standard, IEC 62453.

The second technology is Electronic Device Description Language (EDDL), and it is associated with process industry organizations like the Fieldbus Foundation, Emerson Process Management, the HART Communication Foundation, Profibus International, and the OPC Foundation. It, too, is independent of communications protocol and can thus integrate data from HART, WirelessHART, Foundation fieldbus, and Profibus devices in the same tool.

EDDL is not software, and therefore has no tightly coupled procedure calls that could fail. If the EDDL declaration is faulty, the host will report this just like a web browser reports there is an error on an HTML page.

Moreover, since EDDL is not software, malicious code cannot latch on. It, too, is an international standard, IEC 61804-3.

Complements, redundancies

Over the years, protocols and processes have converged. The lines between discrete, factory, batch, and process control have blurred on the one hand and maintained some identity on the other.

The convergence of FDT and EDDL is not far off. FDT and EDDL aim to do the same thing at the plant, present real-time data in a consistent format that makes plants operate at peak performance, safely, and efficiently without confusion.

End users eventually became enamored of and partial to one or the other of the device managing tools. Soon both tools were in plants. Eventually vendors began to offer and support FDT and EDDL.

Out of all this mutual support came a new cooperating organization, FDI, or Field Device Integration, which aims to streamline device integration for users and suppliers. The Fieldbus Foundation reported on this organization’s development this past spring in the Fieldbus Report.

Major control equipment suppliers and user organizations are cooperating on the FDI framework that will support the growth of intelligent instrumentation technology around the world.

The basis for the FDI technology started out at the “itm” Institute of Munich’s Technical University and was first presented to the public at the NAMUR (International User Association of Automation Technology in Process Industries) 2006 Annual General Meeting under the name FDD UA.

The Steering Committee of the EDDL Cooperation Team (ECT) and the FDT Group, is seeking a common solution for FDI, with a number of development milestones already accomplished.

The FDI team has worked to identify use cases encompassing all facets of plant operations. The team has drafted an architecture concept that meets the needs of each technology as they migrate to a common standard.

The ECT/FDT agreement on FDI incorporates the best aspects of the EDDL and FDT solutions, and eliminates redundancies where they may exist. It does away with double efforts for customers and vendors, preserves backward compatibility, and operating system independence.

Ultimately, FDI will ensure compatibility Device Description Language Device Type Manager-based Device Descriptions. The solution will be applicable to any field-device-communication technology, as well as all hierarchical and heterogeneous network topologies.

Timeline of development

In 2003, the industry’s three leading field device foundations, Fieldbus Foundation, HART Communication Foundation, and Profibus Nutzerorganization, signed a cooperative agreement to develop a common specification for graphical visualization and persistent data storage enabled by EDDL.

In 2004, OPC joined the cooperation team. With EDDL an established IEC standard, it made sense for the OPC group to base its data structure on the same standard and to work with the other organizations to develop a standard interface to the Unified Architecture.

In April 2006, the FDT Group joined the ECT because of a technical agreement to jointly develop a new common standard for device integration. The Steering Committee is comprised of the presidents of each foundation, plus one representative from each organization’s membership.

The draft FDI architecture concept and the complete inventory of use case analyses are finished. Some of the key forces pushing the draft are ABB, Emerson, Invensys, Rockwell Automation, Siemens, and Yokogawa.

Current FDI efforts focus on completing two remaining documents. The first is a functional specification detailing how to combine the benefits of EDDL, FDT, and the OPC Unified Architecture to best effect. The second will be a comprehensive technical specification. Release of the final functional specification will be mid-2010.

EDDL software humanity

Beyond the timeline and logistics of FDI development lies a future of integration efficiency, ease of use, and lower costs to the user. The description of EDDL itself that plays on the organization’s web site is as apt as any of what we can expect to emerge in the final specification (www.isa.org/link/EDDL_wp).

When devices from multiple vendors began appearing together and using bus technologies, there were difficulties accessing and fully using all device features. Many plants were not able to use the device-management software part of their asset management solutions to full potential.

A new concept was necessary to achieve greater results with digital bus technologies. 

EDDL (IEC 61804-3), with enhancements, makes bus technologies come alive and easy to use in exactly the same way the World Wide Web made the old Internet come alive and so easy anyone could use it.

Systems using EDDL make maintaining intelligent devices much easier for technicians and enable digital bus technologies to derive greater results for the plant.

A consistent look and feel is possible despite the fact that each device manufacturer independently decides the display content in their way.

Plants often use a mix of Foundation fieldbus, Profibus, HART, and WirelessHART. Using different software for each protocol is impractical and difficult to learn.

Plants have many kinds of devices such as a variety of transmitters and analyzers, drives, positioners, and actuators.

Using different software for each model would also be impractical.

Driver programs for each

In the past, complex devices such as radar level transmitters and variable speed drives each had stand-alone software for setup and diagnostics. This was difficult to use because each application had a different look-and-feel, that is, screen appearance and navigation was different for each device.

Another solution used driver programs for each device type and executed them under a common title bar but did not solve the ease of use problem because driver programs are still fundamentally different software, by different programmers, with different ideas, with an individual look-and-feel.

If the technician has to stop to think and pay attention to the software, this momentary difficulty can derail the technician’s train of thought. It interferes with the task.

Unfortunately, flexible and innovative user interfaces have the drawback that technicians cannot apply what they learn for one device type to other device types throughout the rest of the system. For instance, in another device the buttons are not where the technician expected. The technician is more likely to make errors.

During normal plant conditions, inconsistencies in operation between different devices are merely a frustrating nuisance that reduces productivity. However, during abnormal plant conditions, these same inconsistencies between devices can actually be dangerous.

During critical situations, the technicians must be able to act quickly, often under pressure. However, when different devices operate do not operate in the same way, the technicians will not have learned to perform the right keystrokes automatically, and they will lose precious time searching for functions and may even make mistakes.

Therefore, it is important device management software and tools work consistently for all devices making use intuitive and reducing mistakes, particularly under stress.

Monotony of design useful

Repetition is the mother of learning. When all devices operate the same way, the technicians will not forget how to do their jobs.

EDDL makes sure devices display consistently regardless of the protocol being HART, Foundation fieldbus, Profibus, or WirelessHART, and regardless of manufacturer, and regardless of it being a radar level transmitter, valve positioner, variable speed drive, or pump health monitor, or other.

When using software, there is a learning phase when we seek to master it. If we use it repeatedly, use becomes automatic without thought or conscious effort. It is like riding a bicycle.
The key to interoperability is to create a user interface that allows the technician to quickly develop automatic behavior, to use the system without having to stop, think, and pay attention to it.

This makes it easier to learn and use, increases productivity, and is more fun. When the system is consistent, learning while working on one device makes the technician automatic on all, or at least greatly reduces the time it takes to learn the rest.

Thanks to repetition, usage becomes second nature. The technicians will have the clicks and key strokes at their fingertips. It is important to make the user interface consistent so technicians learn it and it becomes automatic.

To make a user interface that a human can operate automatically, constraints have to be on creativity in order for automatic habits to form. The user interface must be monotonous such that sequences of actions combine into gestures, which, once started proceed automatically.

The technician cannot routinely pay attention to which kind of device and the task at the same time. Therefore all devices should work the same way, for instance to apply an edited value, how to print, how to get help, and how to pan/zoom on the graphs and charts, and the like.

EDDL reduces inconsistencies between different device types by using the same common user interface elements across all devices and eliminating unnecessary creativity such as overly artistic display.

ABOUT THE AUTHOR

Nicholas Sheble (nsheble@isa.org), InTech senior technical editor, writes and edits System Integration feature stories.

Related Files