DCS Disasters

This Month We Join an End User Who’d Like Her Off-Hours to Be Less Subject to Distress Messages from Her Place of Employment. Dang! Cletus Been in My DCS!

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This article was printed in CONTROL's May 2009 edition.

John RezabekBy John Rezabek, Contributing Editor

It’s like this, you come home to find muddy footprints leading through the family room and learn that the kids let the cable guy in. He exchanged your hardware, lost all your favorites and all those Tivo’d “Dancing with the Stars” episodes you hadn’t watched yet. This leaves you with that sense of violation, of having an inconsiderate chucklehead trudge through your treasures and louse a few things up along the way. This is what it’s like when Cletus the Instrument Tech has his way with your DCS at 3 a.m. on a Saturday.

Now, Cletus is an experienced tech with several levels of CCST credentials to his name and cares about doing a good job. But fieldbus has thrust him―maybe unwillingly―into the once-forbidden world of DCS engineering consoles. While fairly decent with the mouse, Cletus’s fingers are less delicate than those of your typical DCS priest, having been shoved in tight places, around sharp objects, doing steam tracing, and occasionally soaked with some less-than-friendly hydrocarbon substance. He’s good and experienced, but when it comes to seeking out fieldbus diagnostics, methods and function blocks on the DCS console in the middle of the night, this is new territory for him.

Last month I spoke with a process control engineer who works at a big petrochemical complex near the Gulf Coast. Their fieldbus installation is a few years old, but the DCS types still feel as if it was “railroaded” in by their field device people. She described a situation in which middle-of-the-night instrument maintenance caused various degrees of mayhem, for example, when her local Cletus put the wrong function block in “out of service” mode. Selecting the wrong block can mean the operator no longer has manual control of an important valve while the maintenance fix is being performed. Operators tend to find this unacceptable! 

“I’m tired of getting calls in the middle of the night,” she said. “Even if we don’t get a call at 3 a.m., finding the ‘tracks’ of the uninitiated in what we thought were our elegantly crafted control strategies is a lousy way to start the day.”

If you’ve begun implementing fieldbus, I hope you’ve prepared for the demise of the barriers between field instruments and the forbidden city inside the DCS rack room. They’re coming down. If you didn’t prepare, I think you’ll need to schedule a “group hug” ASAP. There may be some rough seas ahead.

True, digital integration of field devices means the line where the system stops and the field begins –disappears forever. I’ve been around long enough to have worked before this barrier came to be, when the same discipline and the same engineers did everything from orifice plates and thermowells to field devices to controllers. We sort of cordoned off the DCS back in the 1980s and created the “system engineer” role. While that division may have served its purpose―saving us from having to train every instrument tech in the shop on the very reliable DCS―fieldbus may take you back to a possibly less comfortable paradigm.

Even our counterparts on the supplier side of process control have issues with this paradigm shift, as field device champions sometimes aren’t even in the same time zone as their host-system brothers and sisters. I’ve been asking my favorite suppliers to get their divisions to play nicer with each other for years. There are improvements, but, as in our own organizations, fiefdoms of the old paradigm still linger on.

Before hydrocarbons are coursing through your fieldbus-capable flowmeters and control valves, users will benefit from gathering all the stakeholders from operations, instrument maintenance and control systems and walking through scenarios for troubleshooting and maintenance. Clear procedures, thorough training and a good test bed for practice will help avoid the stress some users experience when they’ve relied too much on OJT (on the job training) or DOE! (do-oops-educate!) If your contract and work practices allow it, involve operations in the commissioning of fieldbus systems―there’s nothing like operators to look out for their best interests―and their comfort and familiarity with the fieldbus infrastructure will pay dividends when “midnight Cletus” answers the call-out.

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