Control Engineering

Peter Welander

Control in the field: Still an issue?
April 3, 2008

There is an interesting response to our article, Fieldbus: Growing Globally. (You'll see the responses if you scroll all the way down to the bottom of the article.) Dick Caro makes the point that Foundation Fieldbus has the capability to do control in the field because end users wanted to "remove control strategy from the proprietary DCS suppliers." The result was that instrumentation suppliers built this capability into the devices because customers demanded it, whether they wanted to or not. Moving this capability to the devices made the DCS less expensive.

An valid point certainly, and one that users have exercised in many applications. Others have taken the contrary position that including control capability only makes the individual devices more costly because that overhead has to be built into every device, whether it's needed or not. Any savings on the DCS is simply shifted elsewhere. Moreover, I suspect some DCS providers think they can do a better job of optimizing loop performance if it is centralized.

It reminds me of a discussion I overheard in a very nice restaurant some years ago. This particular place had a well known chef. A patron at a nearby table was asking the waiter if a particular entrée would be cooked at table side. I imagine he was hoping for some drama and flaming to impress his date. The waiter replied that the chef wanted to do the cooking in the kitchen and leave the tables to the waiters and waitresses. Controlling loops, like having Steak Diane, seems to be a matter of taste.

Posted by Peter Welander on April 3, 2008 | Comments (0)