John Rezabek is a process control specialist for ISP Corp., Lima, Ohio. Email him at [email protected]There goes Al.
Like many sites, we’re watching many years of knowledge and experience walk out the door. But Al was one of those board operators who made our instrument maintenance jobs more interesting. When he was on the DCS console, he’d have some obscure measurement he wanted us to check — points no one else seemed to care about. So our instrument tech might get a little cranky when Al was on day shift, and he had to climb around to verify or validate a reading that concerned only Al. Why did he worry about these measurements to which no one else paid much attention?
As measurement and control specialists, we might neglect to ask our "end user” why a particular measurement is useful or important. Did Al share his insights with any of his peers? And what happens when his much younger successor asks the old tech to climb a tower to verify a reading? Will he or she get the same respect, service and cooperation when they ask us to fix the funky troublesome measurement everyone else seems to tolerate or ignore?
For example, why don’t the two measurements on an intermediate storage tank agree? Our storage tanks have been fitted with redundant level transmitters in an effort to comply with overfill/spill protection concerns and process hazard analysis (PHA) recommendations. While secondary containment exists in the form of tank dikes and a closed sewer system, the consequences of a single erroneous measurement causing an incident justifies two transmitters on every tank. If you’re like us, you’re measuring the level with a couple differential pressure transmitters that have a quoted accuracy of some fraction of a percent. Why not expect the levels to agree consistently to the same tolerance? But so what if they’re off a few percent, so long as one or the other keeps us from exceeding the high-high level, or ensures the floating roof doesn’t rest on its stands when the level is low?
[pullquote]Many levels are among the most ubiquitous and perhaps some of the most uncertain measurements we make as I&C professionals. Many are expressed in percent, and the less jaded observer would justly ask us, "percent of what?” Sometimes we go to some pains to make the measured percent match a level gauge. Sometimes there isn’t a gauge glass or other independent indication of level. Our DP transmitter or radar/sonar/nuclear device is the only insight anyone has before some undesirable consequence ensues. If we’re not converting level to inventory (volume) for custody transfer, it can be one of the easiest measurements to write off as a "trend.”
The process plant workers who are headed for the golf course have been agents in the culture that determines what’s been tolerable or acceptable. Maybe your site has an "Al” whose sensibilities motivate him or her to be a gadfly for measurement certainty and validation. But too often, we’ve settled into a mutual comfort zone where smooth sailing through the shift is given priority over questions and forensics that might rock the boat. Will the same levels of compromise be passed on to our successors?
As providers of measurement and control, our customer focus is not just the investor who’s financing a project or the project manager beating the drum to meet cost and schedule. Whether you’re an engineer specifying a precision measuring device, a systems person devising HMI and control strategy or anyone in our discipline’s entire supply chain, your ultimate customer is Al and his crew mates. The CFO may be writing the checks, but plant managers lose sleep worrying about where their crews might take the plant. Shouldn’t our focus be to deliver the most truthful, precise and robust depiction of an otherwise inscrutable process?
If you’re still specifying and installing analog 4-20 mA control systems in the 21st century, do you think "future Al” will notice or care? Having interviewed and trained members of Gen X and Millennials to take the helm of highly hazardous processes, I’d say, "You bet!”
