Over the past five years, the battle over networking protocols for plant automation systems has settled down. The days of highly proprietary protocols are gone. Major open standard networking protocols have emerged. DeviceNet, Foundation Fieldbus, Hart and Profibus protocols can handle a mix of device vendors, and all of these protocols have substantial user groups sharing information and contributing to the technology.
One controversy has heated up recently, however, in the territory of the language used to communicate with devices. Though EDDL (electronic device description language) is enjoying increasing acceptance, the recent emergence of FDT (field device tool)—which uses Microsoft Windows—has set off alarms among those who believe it complicates the device language field, as well as those who don’t want to be a slave to Windows. Others, however, see FDT as a handy tool to manage diagnostics at the host level.
Battle lines
Both EDDL and FDT are relatively new configuration languages, though EDDL is a second generation of DDL, the data definition language originally developed for the Hart protocol. FDT was introduced five years ago by ABB and has been accepted by a few vendor organizations. In general, ABB, Invensys/Foxboro and Rockwell Automation are pro-FDT, while Siemens and Emerson favor EDDL.
One of the big objections to FDT is its connection to Windows. “The FDT is a device type manager or DTM,” says Dave Glanzer, director of technology development at of the Fieldbus Foundation, of Austin, Texas, the organization that manages Foundation Fieldbus in North America. “It’s really doing the same thing as EDDL, but it’s a Window-based program, while EDDL is an open platform. So when Windows changes, you have to change everything.”
Glanzer notes that many of the network protocol groups have adopted EDDL as the standard configuration language. “We use EDDL. It’s what we use to describe a device,” says Glanzer. “EDDL is used by Hart, Profibus and the Foundation Fieldbus.”
Network expert Dick Caro, chief executive officer of CMC Associates, a networking consultant company based in Acton, Mass., agrees with Glanzer that EDDL is gaining quick acceptance because it has the blessing of the major network protocol groups. “EDDL came from an international standards group that created Foundation Fieldbus,” says Caro. “Over the next couple of years, it will migrate to the International Electrotechnical Commission (IEC), and most industrial automation standards are IEC standards.” Caro notes that vendors have already picked up on EDDL’s acceptance by the network protocol groups. “The instrumentation vendors support the network protocols, so they’re moving to EDDL.” He predicts that as EDDL reaches greater acceptance, FDT will fade away. “When EDDL is adopted across the board by all of the bus organizations, the need for FDT goes away.”
On the FDT side, Charlie Piper, product manager of the Fieldbus Program for Foxboro, Mass.-based Foxboro Automation, a division of Invensys, notes that FDT is particularly effective at managing device data inside the host computer. “FDT is a standard for application program interfacing inside the host computer so a program from a device vendor can interact with a program the host provider has on the same personal computer,” says Piper. “We don’t think of EDDL and FDT as rivals. Rather, we think the device description [DD] technology is vital in terms of describing the device to the host computer, but the DD languages alone are not sufficient. They don’t provide a complete interface specification that can fully define the interface between the device vendor and the program the host computer uses for the engineering and maintenance environment.”
Glanzer, of Fieldbus Foundation, agrees that the natural space FDT will likely settle is on the host rather than at the device level. “We think users will end up reading EDDL from the device to the host; then they’ll put the FDT into the host cloud so they don’t have to worry about it,” says Glanzer.
Pragmatic
Brian Oulton, product marketing manager for Logix/Netlinx at Rockwell Automation, has a very pragmatic take on the pros and cons of FDT and EDDL. “Users need to use the same criteria for choosing configuration languages as they do for choosing a network,” says Oulton. “You find the devices you prefer, and you use the standards and formats that those devices adhere to.”
There are certainly mixed messages about the value and usefulness of FDT, especially given its tie to Windows. But aside from the battle over configuration language, the territory of networking protocol is relatively calm. The widely used protocols—DeviceNet, Foundation Fieldbus, Hart and Profibus—are open, well regarded and focused on specific market segments. Each has specialized uses and all have strong industry support groups.
See sidebar to this article: Networking Protocols
See sidebar to this article: The EDDL and FDT advantages & disadvantages
See sidebar to this article: Running third-party devices through the network
