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A control system by any other name

Sept. 11, 2017
Is there really a difference between a DCS, a PAC, a PC and a PLC?

I recently took the DCS/PAC/PC/PLC survey and thought this was one of the dumbest surveys I have seen (“PLCs and PACs,” August 2017, Market Intelligence Report). Sorry for the bluntness.

I have been doing control engineering for more than 30 years. I have watched the snobbish discussions whether DCS is better than PLC is better than PC for years, and now we are trying to separate PLC from PC from PAC. There are lots of leading questions that you will try to make decisions with.

They are control systems—nothing more, nothing less. Do you primarily use PLC/PAC/PC for analog, digital HMI? We use it for all of them; it’s not a choice. What is your primary job function? All of them—again, no choice. What is your view of what a PAC is? Again, it is a 2017 controller that incorporates the advancement/evolution of DCS and PLC and PC control . Just as I started as an industrial instrument technician, working on pneumatic controls, and then went to an electronic controller, which then went into a distributed control system (DCS), which then was converted from a Unix mainframe to a Windows PC, which is now a hybrid combination of those items.

My job has not changed any more than my note cards, which went into a PDA, which went to a iPad and went to an iPhone. Yet, I still have my to-do list, calendar and phone calls with that one tool. It’s just a tool.

I love people who get hung up on how distributed control systems are better than programmable logic controllers, which are better than programmable automation controllers, which are better than PCs. They are all just tools that do what they’ve always done.

Yes, I am now a network Microsoft Certified Systems Engineer (MCSE) engineer. I do virtualization. I write code in 10 different languages. I draw CAD on a computer vs. a drafting table. I send email instead of snail mail. I order from Amazon instead of going to the store. Is that a technological breakthrough of epic proportions? No, I just buy stuff.

This all reminds me of the lawyer’s leading question: Do you still beat your wife? Yes or no, the lawyer will get the answer that he/she wants with that question. You got no valuable information from that survey from me, and, if you got none from me, my guess is you got none from anyone.

I am a lifelong learner who started as a craftsman and am now an engineer responsible for multimillion-dollar controls projects. I have had to adapt and learn as my craft has changed over 30 years. In the end, I do things differently; yet I do the same thing that I did 30 years ago. I have won controls programming contests sponsored by Microsoft, Rockwell Automation and others. I’ve been featured in magazines and presented at national conferences. But, again, as I look over my career, I have heard mainframe guys say PCs will never happen, I’ve heard DCS guys say PLCs are just toys, and, now that they have morphed into the middle, we are trying to say one is different from the other to segregate them into levels of importance.

Sorry for the rant, but for some reason this survey annoyed me and hit me the wrong way as being impossible to answer.

It reminds me of my city sending out a questionnaire asking us if we were for wind-generated power to be supplied by the city as a renewable resource offering. They didn't ask if we were interested and willing to pay extra for it, which would yield a much different questionnaire result. How can you possibly be against renewable energy?

Data is only data until you turn it into information. Information is only information until you turn it into knowledge. Knowledge is only knowledge until you turn it into wisdom. This survey will result in no usable information.

About the author

Dave Ferguson is control systems engineer at Blandin Paper, UPM-Kymmenem in Grand Rapids, Minnesota.

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