The Importance of a Project Specification Document

Posted by Control Engineering Team on June 26, 2012 @ 10:41 am

Leaving Project Specifications Blank or TBA is a Recipe for Project Trouble

Much has been written on the subject of creating legal contracts, often including statements like, “Good contracts make for good clients,” and “Good contracts lead to good customer relationships.” Contracts are important. In addition to stating legal and financial requirements, contracts define what is to be done for the client. Just as important as contracts, proper specifications are needed to identify clearly how the contract requirements are to be satisfied. We have written this to remind our peers about the importance of specifications to any engineering project, and to explain to any prospective clients that we know how to deliver what is expected. When we say, “We get it,” the functional specification is where “it” is defined.Continue Reading

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Why Aren’t More People Getting on the Fieldbus Bus?

Posted by Bruce Brandt on June 19, 2012 @ 8:55 am

After being involved in a number of migration projects, I’m surprised at how few of these considered taking advantage of the extra capabilities of fieldbus-based instruments, drives and positioners. This is not a new phenomenon, but it was more understandable in the early years of the technologies. To some degree the fault lies with the manufacturers. Fieldbus communication was marketed as being a way to reduce the number of wires required and the size of the cabinets required. To a great degree the real benefits of its ability to support smart instruments was a marketing afterthought, “Look at all the room you can save and, oh by the way, you get this extra information.” As a result, the typical migration project team says, “We already have all these HART instruments that give us the extra data and we’re not pulling any new wire, so why should we change?” Continue Reading

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Doing Your Homework – Part 1

Posted by John Clemons on June 13, 2012 @ 7:50 am

You’ve probably heard me talk before about the idea of operational excellence. In additional to operational excellence, I’ve probably called it manufacturing performance, predictable manufacturing, or even reliable manufacturing. It’s the basic idea that in manufacturing there’s just some things that you have to do right. Like attack the waste streams and control variability and ensure consistency. You need to adhere to your schedules, achieve regulatory compliance, and work on ways to optimize performance. I could talk about it all day, but I’d like to do something different. I’d simply like to take these ideas and turn them back around to you.  I’d like to ask you to go do some homework. I’ve got some questions here that I’d like to ask you to think about. Or even go out and investigate a little bit. I bet there’s some of these questions that you don’t h... Continue Reading

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Intersections of Manufacturing and Process Control

Posted by Sergei Kuznetsov on June 12, 2012 @ 9:06 am

Have you ever thought about how many average families have been changed by having GPS devices in our cars? Just think back to the (not so) good ol’ pre-GPS days when you pretended you knew where you were going, only to find out you didn’t, and you never heard the end of it. When those wonderful gadgets came along, they put a stop to all the arguments about directions. Yet the change snuck up on us so quietly, it went mostly unnoticed. I see the same thing happening in our industry with variable speed drives (VSDs), including variable frequency drives (VFDs) and inverters. Yes, we all know you can reduce energy consumption while improving efficiency and process control by using VSDs to drive pumps and blowers instead of using flow restriction devices. But that’s not what I want to talk about. What I want to focus on is how much the cost of modern VSDs has dropped in recent years.... Continue Reading

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From the Trenches: Distillation Columns – Internal Reflux Control

Posted by Jim Ford on June 6, 2012 @ 8:31 am

Distillation columns are one of the most often used unit operations for separation and purification in the process industries.  They can also be some of the most complex to operate and control, because they involve two-phase, multi-stage, counter-current mass and heat transfer (each tray or segment of packing is a theoretical equilibrium stage).  The greater the number of trays, the longer the time constants related to composition changes. For a two-product distillation column (top and bottom product), there are typically five degrees of control freedom (control valves):

  • Reflux flow
  • Top product flow
  • Reboiler heat input flow
  • Bottom product flow
  • Pressure control valve (the specific location depends upon how the pressure is controlled).
Three of these valves are needed for inventory control (reflux drum, column bottom... Continue Reading

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