Changing Trends: PLCs, PACs, PC-based controls, FPGAs or even DCS?

Control choices can vary, sometimes by application or sometimes by engineers’ preferences or expertise.

By Mike Bacidore, Chief Editor

Jim Barry, Michael Batchelor, TJ McDermott and Rick Rice—these are individuals you need to know. Four of the most expansive thinkers in the machine-building technology space, these engineering veterans comprise the Control Design Editorial Advisory Board.

As an introduction, they shared their thoughts on a variety of topics, from motion control and wireless sensing to control platforms and cybersecurity. Here is their take on engineers’ preferences from PLCs, PACs, PC-based controls and more. 


 

CD: Control choices can vary, sometimes by application or sometimes by engineers’ preferences or expertise. How much needle movement are you seeing overall regarding the use of PLCs, PACs, PC-based controls, FPGAs or even DCS?

Michael Batchelor: We are seeing much greater use of PACs in the field, although I suspect many of them are underutilizing their capabilities. The modern PAC’s ability to interface with information systems —another example of the coming merger—give it substantial power on the plant floor that is just beginning to be tapped. I fully expect in the future that a PAC interface that exposes methods and values for remote call will become normal, and this will closely resemble the object-oriented paradigm in many modern programming languages. This will increasingly blur the lines between PACs, PC-based systems and DCS.

TJ McDermott: I still think the distinction between a PLC and a PAC is artificial and driven only by marketing departments. PLCs and PACs still rule for machine or system logic. PCs collect data from those controllers but don’t cause system downtime when PCs invariably need reboot.

Rick Rice: I have been in this industry for more than 30 years. I learned to program with GW-BASIC, C, C+, Prolog, C++, Visual C and on and on, in college and beyond. Coming out of college, I grew up, so to speak, on PLCs. When PACs came out, I was one of the first to jump in with both feet. I was fortunate to be a part of the team that implemented the first large-scale rollout of the then-new Allen-Bradley ControlLogix platform with ControlNet and DeviceNet right down to the individual sensors on the machines for a large mining concern here in North America. I ran into PC-based controls for the first time in 2001. While I am not as familiar with FPGAs or DCS, I can definitely follow the progression of the think tank into these technologies.

I can do some very creative things with a PLC, and this carries over into the PAC world with the added feature of structured programming, function blocks and such.

– Rick Rice
At a high-level view it can really come down to the experience or preference of the programmer. I think, generally, that older programmers like me will prefer PLCs or PACs because they still adhere to the relay logic approach to program development. I can do some very creative things with a PLC, and this carries over into the PAC world with the added feature of structured programming, function blocks and such. Younger folks that came through high school or college with some experience with PC-based controls might argue that they can build a better mousetrap, but I would argue that my programs and algorithms can be diagnosed and followed by a much larger audience than their computer-based applications.

I can’t honestly see a migration away from PLC-based systems. While the programmers definitely tend to come from institutions of higher education, the people operating and maintaining the equipment will continue to come from the same sources. They are our neighbors and friends, and they are the backbone of our workforce. This trend will not change. I think that automation providers who put more firepower into the PLCs and PACs will continue to lead the pack in automation. A good PLC programmer with some good hardware can create a system as powerful as the PC-based systems.

Here is a good analogy. When the printer in the office messes up, we call the specialist in to make it work again. When my case packer messes up, I’ve got two or three people available in-house, already on my payroll, who can take a peek inside and tell me what is going on. This is how it is with PC-based systems. They can do some pretty fantastic things, but, if I need a company representative to get my line up and running again, then it is of little use to me. If the line has to be down for a day or two while a specialist comes to town, then I’m not producing, and, if I’m not producing, then I’m not making money.

A printer is a commodity. If it truly fails, then I toss it out and buy a new one. A packaging machine is an investment. I expect to get 15-20 years out of it. I’m not convinced that a PC-based system will give me that kind of return on my investment.

Click here to meet the Control Design Editorial Advisory Board. 


 

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 Main Image courtesy of Danilo Rizzuti at FreeDigitalPhotos.net

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