1 April 2006

Field device complications

By John Rezabek

The automation industry's ability to confuse its users remains sharp.

Don't let anyone tell you field device tools (FDT) offer distinct advantages over electronic device description language (EDDL). Neither one is developed enough (in commercial offerings) to make any clear judgment, as far as I've seen.

I have not seen EDDL in the flesh, but it will certainly do as much as the current DDL, which does, in fact, include as many diagnostics as the vendor cares to display.

The problem is there is no standard way for your DCS to display them. If the DCS people make a beautiful interface for one valve, it won't necessarily work for other vendor's valves, or even later revisions of the same vendor's valves.

I see it even now, if I pull in (via OPC) device diagnostics or secondary variables.

As soon as that device changes, many times the link ceases to function, and the variable (case temperature, for example) has to remap.

This gave the few vendors, with leadership in both DCS and field devices, the ability to offer features their competitors couldn't. And (surprise!) they used it to leverage sales both ways.

That is, "if you like our valves, you should use our DCS," or "if you like our DCS, you should use our valves."

If you were a competitor, you were put in a difficult circumstance. In the West, we call this beating your competition, and we generally think it is an OK thing. It is less OK if you are the one getting beat.

So, some (or one, you could argue) of the dominant players were seeking market differentiation by offering super-deluxe diagnostics (for example, valve signatures). But you had to buy their valve and their DCS.

Few other suppliers had competitive offerings in both areas (valves and control systems), so they had difficulty doing anything amazing on their DCS.

Or, when brand-X valve was seen on the winning DCS, it looked pale by comparison to the green ones.

FDT was born, in my opinion, to combat this single-source incentive/advantage.

For it to work, the device vendor has to supply the diagnostic applet (something to calibrate a valve or instrument), and the DCS vendor has to provide the platform to run it.

EDDL will work the same way, and most of the people trumpeting the virtues of FDT said they would support EDDL as well.

The distinction of EDDL is it comes from the Fieldbus, Profibus, and HART Foundations, so it has the promise of being more standardized across all vendors.

FDT is a loose association of vendors from all parts of the industry and some users. Why we need two such organizations is perhaps the same reason we need eight different fieldbus standards.

About the author

John Rezabek is an ISA senior member. He is the process control specialist for ISP Lima LLC, Ohio BDO plant, formerly a BP facility. He has a BS in systems engineering and has worked in refineries and chemical plants for 25 years. Rezabek was the site implementation manager for the first application of Foundations fieldbus HSE and Flexible Function Blocks in an operating chemical plant.


There is some controversy in the territory of the language used to communicate with devices.

Though electronic device description language (EDDL) is enjoying some acceptance, the recent emergence of field device tool (FDT), which uses Microsoft Windows, has chagrined those who believe it complicates the device language field.

In addition, of course, there are those who, on principal, don't want to answer to or depend on Windows.

Others, however, see FDT as a handy tool to manage diagnostics at the host level.