Anybody who's worked in technology for longer than about a week begins to understand, if only dimly at first, the problem of competing technologies and its implications for one's technical life. Mac or PC? iOS or Android? Wired or wireless? Foundation Fieldbus, Profibus or HART?
Deciding which way you want to download your music files or use your cell phone is one thing. When you're talking about connecting hundreds or even thousands of field devices to your PLCs or DCS, the decision is a bit more fraught. Once you've committed to one method, you've committed to a particular way of doing things and sometimes a particular set of vendors. If, like most operations, yours uses technology from multiple vendors, you now have the problem of getting multiple systems and architectures to work smoothly together, and making sure the legacy systems work with the new ones, all of which inevitably adds time and money to any project, not to mention frustration and more gray hair.
The Past Is Prologue
Device management, the business of organizing and connecting the myriad of field devices in your operation and then making best use of the information gathered from them, is no different—which brings us to the alphabet soup that surrounds any discussion of device communication technology.
The first two technologies and acronyms you need to learn are Field Device Tool/Device Type Manager (FDT/DTM) and Electronic Device Description Language (EDDL). These are the two major technologies that, under the covers in your devices, make their connectivity possible.
The two technologies are at the same time complementary and competitive. So, in the early days at least, their history sounds a bit like the notorious fieldbus wars. Even now, the true believers in both camps carry on arguments not unlike those heard in coffee houses about Macs and PCs. There are details and nuances about each that only a true techno-geek—or a medieval theologian—could love.
For the rest of us, here are the distinctions. EDDL is used by major suppliers in the process industries to describe the information accessible in smart field devices. It supports device diagnostics and calibration, and it can be used in any device from a handheld terminal to a process control system.
FDT is the IEC 62453 standard. Its roots are in discrete manufacturing, and since the early 1990s, it's been supported by vendors with interests there, such as ABB, Endress+Hauser, Invensys, Metso and Siemens. But, it's also used in the process industries. It supports more than 16 protocols used in the process industries and factory automation, including Foundation fieldbus, HART, Profibus/Profinet, DeviceNet, Interbus and AS-Interface. It has some advanced functions that EDDL does not, such as graphical representation of information. It also works well with complex devices, such as radar level gauges. The notable virtue of FDT is its independence from a particular communications protocol and from the software environment of the host system. Any FDT-enabled device is accessible from any compliant FDT host using any field communications protocol.
FDT is also more complicated than EDDL. It has two parts: the frame application, FDT Frame, and the Device Type Managers (DTMs), which are available for field devices and communication equipment. Think of the two as the equivalent of the print manager in your Microsoft Office program and the print drivers. The strong suit of FDT/DTM is its ability to interface with multiple devices and process a high level of diagnostic information.
Larry O'Brien, global marketing manager for the Fieldbus Foundation, explains, "EDDL is like XML for intelligent devices. FDT is more sophisticated software for handling diagnostics. It's more of a runtime environment. It's really good if you're managing information from complex devices, and it has more power than EDDL. EDDL is very simple. FDT has more complexity and the same issues as any Microsoft environment in terms of updates and patches."
It's easy to see how choosing one or the other could be a complicated and frustrating decision, and one that end users might seek to postpone as long as possible, even if it meant doing without the advantages offered by intelligent devices.