FDI: More than another acronym

The FDI (field device integration) Project will have a big impact on the future look and feel of digital field sensors, especially after the recent announcement that host suppliers ABB, Emerson, Endress+Hauser, Honeywell, Invensys, Siemens and Yokogawa have joined the FDT Group, Fieldbus Foundation, HART Communications Foundation, OPC Foundation and PROFIBUS in pushing not only the development of this new standard but also incorporating it in their products.

So what is FDI? In simple terms, when complete, it will replace all EDDL (IEC 61804-3)-based languages: HART, Foundation Fieldbus and PROFIBUS-PA. Obviously, this is a significant portion of the process automation market.

While EDDL is a common text-based description of a device, the text description is normally converted to a "binary DD" through a tokenizer before being shipped with the device. Unfortunately, the format of the binary DD is different for each process Fieldbus even though they originate from the common EDDL language. The above manufacturing company members of FDI have made it a high priority to harmonize the binary DD through secondary standards and tools so the result will be a single binary format file regardless of the protocol of the device.

The EDDL file for each protocol will be processed through a tokenizer, much like it is done today; this also ensures backward compatibility, as we would not want to have to replace all our existing devices as a result of this change. Because each protocol is not exactly the same, but rather closer to 90-percent similar, it will be necessary to create an FDI Developer environment for each of the three EDDL-based protocols to assist them in defining how to "map" the various parameters of each protocol to the appropriate FDI parameters.

The resulting binary file from the tokenizer is then passed to a "packager," where it will be converted to an FDI file. Note that, at their discretion, the device manufacturer will be able to define a user-interface plug-in that is integrated into the FDI file by the "packager" to create the single common file. Foundation Fieldbus device manufacturers have this discretion today as well by creating "extended" function blocks that contain information beyond what has been fully defined by the Fieldbus Foundation.

What is important to end users will be the interoperability of these devices, and that will be insured through the appropriately coloured green "test tool" box, which will provide the necessary check mark from the appropriate organization that the devices are not only compliant with FDI but also backward compatible. This is important when a new device needs to be added to an existing network and everything will have to continue to work together seamlessly.

Lastly, when the device is connected and communicating on the network, the process needs to be "reversed," with the DCS/host converting the FDI information into a format useable by the internal system databases. This is not different than is done today, where each system needs to "interpret" the information from the field to the appropriate database register within the host.

Note that the user-interface plug-in, which will be used to provide improved access to the maintenance, diagnostic and related parameters in the field devices, will use the knowledge gained from the use of FDT technology and combine that with the open interoperable communications capabilities of OPC UA to provide a platform independent solution to the rich data set contained in a modern digital field device.

The working groups hope to have the standards developed by the third quarter of 2010, which means products should start being available in 2011. Do not let this change your plans for using any of these protocols because backward compatibly will be a key to acceptance and a must for the developers/testers.

The good news and incentive for this work with all the device and host manufacturers is that they will now only have to develop and support one, rather than three, device description standard, which reduces development and support costs. For end users, this means reduced system complexity and better access to richer data features for all devices on the network. _

Ian Verhappen, P.Eng., is an ISA Fellow, ISA Certified Automation Professional and a recognized authority on Foundation Fieldbus and industrial communications technologies. Feedback is always welcome at iverhappen@gmail.com.