Is FDT good for fieldbus and device networks?

Gareth Johnston, fieldbus communications specialist at ABB Ltd., states, “The value of FDT is that FDT provides full access to intelligent device features such as set-up (especially for multi-variable devices) and diagnostic information (signature analysis—clear language maintenance description). The DTM can use these to execute automatic commands to simplify device set-up. It also provides a flexible communication path that allows users to select the communication device (remote I/O with HART Passthrough, USB HART/ProfiBus modem, etc.) regardless of the vendor.”

For devices that don’t have a DTM yet, there also are FDT applications on the market that interpret EDDL applications on the fly. This makes it possible for end users buying equipment without FDT support to generate a basic FDT for use in their asset management or host system.

Because FDT/DTM is an open standard, it enables non-DCS device vendors with a level playing field for all device manufacturers. This helps them compete more strongly, using their enhanced diagnostics capabilities, and providing full access to these capabilities in any environment. Unless the snap-ons and related “add-in” pieces of software used to communicate with the asset management system are made available as an open standard, as was done with DD technology and is being proffered by FDT Group, the owner of the software for which the add-in is developed will remain in control of the way data is presented and made available.

The recently released FDT Style Guide will provide a more consistent “look and feel” for future DTMs, while also satisfying the recommendations of the NAMUR working group on the features/requirements of an effective asset management system. As a result, it’s likely that most DTMs will provide a similar “look-and-feel” device interface that is very similar to the vendors’ existing maintenance and configuration software tools.

What’s in the Future?
Most control system and device vendors are looking at FDT/DTM to see if or how it fits into their future. It looks like it may be an even better fit after OPC UA is available, though most of the vendors will likely continue to use EDDL for configuration.

Yet another anonymous major oil company engineer is concerned that, “Users will have to maintain a steady push to assure that diagnostics data and alarms are integrated with DCS operator subsystems for effective graphical user interface and alarm management. Vendors have a distressing tendency to segregate these applications into separate systems that don’t share information with operators.”

In addition, after the Swiss National Standardization recently made a new work proposal to the International Electrotechnical Commission (IEC), FDT was unanimously approved as a “publicly available specification” under the auspices of new standard working group IEC SC65C WG14 “FDT.” Following an initial meeting in January 2006, the hope of the committee is that the standard will be completed by October 2007.

Similarly, Profibus Nutzerorganisation e.V. (PNO) and FDT Group have agreed to develop a PLC programming tool, Tool Calling Interface (TCI), as an open tool to integrate the factory automation and process automation environments with one interface. The TCI specification will contain a bidirectional communication channel from the tool to the field device via the PLC programming system. Hopefully, this tool will also be compatible with the IEC 61508 on which all PLC programming software and documentation is based.

Also, FDT-JIG has indicated that FDT is a complementary rather than competitive technology to EDDL. They also acknowledge that FDT has some limitations including:

• FDT is a Microsoft Windows-based technology. As such, it is subject to the inevitable upgrades and operating system version changes with which we have all become familiar. As with all software tools on all operating systems, FDT platforms and device applications will need to be updated occasionally.
• FDT only defines interfaces between system components. As such, FDT components cannot replace DD files, which continue to be an integral part of major fieldbus systems.

There is hope that the FDT/DTM versus EDDL battle soon may be declared a ceasefire, since a member of the Fieldbus Foundation’s board of directors says, “Most of the members of foundation are also members of FDT Group, so the Fieldbus Foundation board needs to make a clear statement on the EDDL/FDT relationship.” Hopefully this can happen at the FF’s general assembly at the end of February 2005.

Using FDT
Achim Laubenstein, ABB’s manager of fieldbus development, says, “FDT is the opportunity for device vendors to provide the application software that best fits their device. One and the same DTM can be used in many hosts without extra effort. This saves costs for the host and on the device side. One can imagine that device vendors especially have a high level of interest in such interface technology.

“When implementing FDT, rather than starting from scratch, we recommend using existing components available on the market. A user should check whether the products he wants to use are certified by FDT Group.”

End-users just want a simple, intuitive way to access, interpret, and understand what’s happening in their process and to their devices. Fortunately, it sounds like the manufacturers also are getting the same message, even though it looks like some are fighting a rear-guard action to protect proprietary technologies from the open systems movement. Hopefully, OPC UA will be the common technology that will enable them to come together in a smooth, unified way.