I was working on a large automation retrofit project of a chemical plant that had numerous thermocouples scattered throughout the structures. A vendor suggested a particular thermocouple card that I had never used, and I was about to proceed with that card when I decided to quickly scan the specs on the card. There was an odd footnote about channel-to-channel isolation that caught my eye, and as I dug deeper into the details, I realized that channels 1 through 4 and channels 5 through 8 shared a common ground on the card.
Now, this plant was older and had a mix of grounded and ungrounded thermocouples. If I happened to get thermocouples from two different columns on the same group of channels, the resulting ground loops would have sent the readings all over the place. Luckily, I noticed this and was able to pursue a different path early in the design process.
Details matter—take the time to chase them.
Concept: If you are not a detail person, either pursue a different career or LEARN to be a detail person. The field of automation demands extreme attention to detail. Wire size, materials of construction, flange size, flange rating, min/max flows, temperature, pressure, etc.—the list goes on and on. Failure to evaluate even one item can have serious or even catastrophic consequences. Check and recheck everything— “good enough” can shut down a plant or even get people killed.
Details: Engineering is by definition a detail-oriented profession, but the field of automation requires almost fanatical attention to detail. Everything matters, which is why instrument spec sheets have so many lines on them. Engineers who just copy/paste spec sheets from a similar transmitter or use a control panel design without understanding it will not last long in this field. Automation is particularly challenging because the engineering skill set is so diverse. In the normal course of a job, automation engineers might find themselves doing mechanical design, electrical design, and chemical process design, and each of those has a long list of details to consider. Obviously, a comprehensive list of the necessary details in the field of automation would take multiple books to cover and cannot be provided here. However, here is a list of examples that will help you learn to chase the details:
• You should never copy or modify a design that you do not understand. A panel hardware design may involve a hundred design decisions—wires and I/O racks are sized for current and future needs, space is left for thermal dissipation, wireway is sized for current and future field wiring, locations for conduit penetrations are allocated, the cabinet is sized to fit in the room and even sized to fit through a particular doorway. If you copy that design and modify it without understanding what went into the original design decisions, you may quickly find yourself in trouble. The panel equipment may start overheating because a larger power supply was specified, or the main breaker may blow on start-up because the inrush currents are higher, etc.
• Read the specifications and understand them. Failing to consider the pressure/temperature limitations on instrumentation can have catastrophic consequences. Failingto look at the electrical details of I/O cards (grounding, leakage currents, voltage limitations, etc.) can turn a start-up into a nightmare. Looking at spec sheets might be the very definition of boredom, but FAILING to look at spec sheets may generate much more excitement than an engineer wants to encounter.
• Learn to color. Young engineers are notorious for working fast but missing details. One of the best ways to address this problem is to pick up a highlighter and learn how to color the lines as you work. If you are checking drawings, then highlight each section as it is completed. If you are doing an instrument takeoff, then color each instrument on the P&ID as it is added to the list. In short, find a document that covers everything that needs to be done, and color it as each item is completed. Checklists (such as those found at the end of this book) can also be an invaluable way to make sure everything has been considered and evaluated.
• Trust, but verify. After an engineering team leader has worked with a team for any length of time, he or she gets to know the strengths and weaknesses of each team member and knows where and to what degree back checking is required. New engineers should probably be 100% checked initially but can be backed off to spot checking once their skills are proven. However, even work done by seasoned engineers should be reviewed to some extent because everyone makes mistakes.
Watch-Outs: Always cross check vendor sizing calculations for instrumentation. Vendors often plug information into sizing software and generate impressive specifications and calculations, but they do not know the process, and they make errors. It is always worth running a rough cross check on their sizing and then reading through the entire specification to make sure the materials of construction are as required for the application.
Insight: Many large engineering firms send a spec sheet with a smattering of process information to the vendors and let them generate the instrument specifications. This practice invites disaster. The vendor cannot possibly know the process details or the abnormal conditions that the instrument might encounter.
Rule of Thumb: Successful automation engineers HAVE to be detail-oriented. If this is not a natural tendency, then learn to color, cross check, or do whatever is required to be detail oriented.
Hunter Vegas, P.E., holds a B.S.E.E. degree from Tulane University and an M.B.A. from Wake Forest University. His job titles have included instrument engineer, production engineer, instrumentation group leader, principal automation engineer, and unit production manager. In 2001, he joined Avid Solutions, Inc., as an engineering manager and lead project engineer, where he works today. Vegas has executed nearly 2,000 instrumentation and control projects over his career, with budgets ranging from a few thousand to millions of dollars. He is proficient in field instrumentation sizing and selection, safety interlock design, electrical design, advanced control strategy, and numerous control system hardware and software platforms.