Growing recent graduates into controls engineers

Posted by Bruce Brandt on June 5, 2014 @ 1:19 pm

Too many recent engineering graduates have never set foot inside a process plant before, or they have very little experience with process control systems.

An old friend of mine tells a story about his first project meeting after joining an engineering company fresh out of school. The lead engineer kept saying that it was a “grassroots project,” so my friend finally asked “How do you make paper out of grass roots?” We’ve all been there in one way or another, but what we do isn’t brain surgery. It isn’t even rocket science—though it’s closer. So how do we teach our new graduates to be controls engineers? Many newly minted engineers have never set foot in a process plant or if they have my experience is they got very little exposure to the process control system. The many control theory classes, from my experience, don’t seem to be very tied to the real world but focuses on the math associated with things like Laplace transforms, feedback circuits and the proportional-integral-derivative (PID) equations with little connection to what happens when the output of that equation hits the real world of valves, dampers, and variable speed drives.

What I find when I teach a new graduate about the day-to-day world of process control is that I have to teach them the basics of process control devices first. Again, depending on the university they attended and their degree they may or may not have heard a certain term, like “normally open contact” or what that means in the context of a process switch. These days even electrical engineers may or may not have a good grasp of physical contacts as opposed to solid state switches. I’m teaching a class right now with a new chemical engineer and was using the very simple example of starting and stopping a pump using two pressure switches and the motor run contact from the starter in a failsafe design. Like this programmable logic controller (PLC) ladder logic diagram:


Source: Maverick Technologies

The training problem was to create a configuration that would accomplish this very simple task, but first I had to explain what the symbols meant, then I had to explain what was meant by “normally open” or “normally closed,” and then I had to explain where the contact labeled with “M” came from. As part of explaining the normally open/closed concept, I had to explain what the difference is between shelf state and normal operation state for a physical switch. Not as simple as you might think because for my logic to work both the low pressure and high pressure switches’ shelf states are normally closed, opening when the pressure goes above 10 psi for the PSL and above 60 psi for the PSH, but in normal operation the PSL will always be open potentially creating confusion about what’s normal.

If I’d drawn it using relay logic conventions it would have appeared that the circuit would always be energized. And therein lies a problem, there are still plenty of plants that use relay logic for things like burner management systems. I’ve just been working on a boiler project where that’s the case. If I give my newbies a copy of the relay logic drawing for programming they’ll likely not realize that the normally closed symbol on the drawing equates to the “examine if closed” function in the PLC, creating a mess. Again, depending on curriculum and institution a new graduate may or may not have ever seen a relay style logic drawing, or—for that matter—a motor elementary diagram.

Other rather basic concepts that need to be taught include: fail open vs. fail closed valves and how that might change their programming; direct vs. reverse acting loops which are handled differently depending on the control system being programmed; fail safe logic implementation; the impact of impedance on solid state switches; the differences in measurement technologies; what happens when a valve is oversized or sticks; and a thousand other things that for those of us who have been in the business for a long time don’t even have to think about.

So what things do you have to teach your new grads and what have you found most successful in making them process controls engineers?

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