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The Many Faces of PACs

Dec. 6, 2013
How PACs Are Defined Isn't As Important As What Each Version Can Do
About the Author

Jim Montague is the executive editor for Control, Control Design and Industrial Networking. Email him at [email protected] or check out his Google+ profile.

The precise nature of programmable automation controllers (PACs) appears to be in the proverbial eye of the beholder. Some developers say they're souped-up PLCs with more processing power, while others say they're a genuinely different, more software-based animal. However, everyone agrees that how PACs are defined isn't as important as what each version can do.

"PAC is a term coined to differentiate from PLCs that traditionally had more rigid functions and lacked data connectivity," says Graham Harris, president of Beckhoff Automation. "So PACs are typically controllers that can allow logic and motion processing to happen in the same space. We say a PAC is a PLC-plus that comes in different shapes. We used to talk about data flowing though companies from sensors to the boardroom. Well, the Internet of Things (IoT) or Industry 4.0 is here now. The real revolution is in making more of these connections and further linking devices and facilities to overall operations. That's the true value of PACs."

SEE ALSO: What Exactly Is a PAC?

To nurture these connections with multi-core processing, Beckhoff is running four core chips in the CX 2000 embedded PC it released last year. This device looks like a PLC or PAC, but Harris says it's closer to four controllers in one and can run high-speed sequential control, high-speed motion, HMI, vision, data connectivity and other applications on separate cores. "Running multiple cores and devices on a common database means better coordination and faster control because the devices can quickly reach in and grab whatever they need, and this is a big IoT enabler," he adds. "It's just like all the handheld PCs, phones, beepers, cameras and video recorders that used to be separate, but are now on the same smart phone. As a result, plant managers are using these PLC-pluses to check energy consumption, reduce waste and find other new things to control." 

Benson Hougland, vice president of marketing and product development at Opto 22, reports that, while PLCs are usually programmed in Ladder Logic and operate by scanning I/O and sequentially solving their logic, PACs employ 32- or 64-bit processors and can use multithreaded execution to carry out several programs asynchronously.

"The power really comes out in the software," Hougland says. "PLC software is limited at the point its hardware no longer supports it, but PACs can take advantage of more capabilities, such as multithreading functions for logic, motion, PID tuning, drives, process control and discrete control."

Hougland adds that PACs aren't always better than PLCs because a PLC is still more suitable and less costly for fast, discrete machines that don't need to share data via Ethernet, while a PAC is better at controlling a platform, running sophisticated applications and transmitting data, but is generally more expensive. "We also see the line blurring between PACs and PLCs, and there's also less price disparity between them," he says. "But if you want to link to a drive, operate a servo system and run an HMI or a bar-code scanner, then you can connect to all of them with a PAC. It can act like a traffic cop, but it's the software that allows them to come together."

Paul Whitney, commercial program manager for Integrated Architecture at Rockwell Automation, stresses that many applications still need the speed and simplicity of a dedicated operating system for reliable control. "Some machine builders that need to streamline their modular machine designs for maintenance and troubleshooting struggle with complex, PC-based controls and code, so they switch to our dedicated, scaled-down PAC," Whitney says. "It can handle two, eight or 16 axes of motion and 100 I/O, which means a small machine can get the same performance as a larger, more complex machine."

Brett Burger, senior marketing manager for embedded systems at National Instruments, adds that, "When users in the past faced complex relay problems, PLCs came along and simplified them. Now users face even more complex problems, so PACs are blending PLC and PC capabilities to solve them too. The next step is to use PACs for advanced control, synchronization and communications, and our response was to add field-programmable gate arrays (FPGAs) to our CompactRIO PACs, which gives them the openness, power and web access of a PC and the ruggedness of a PLC. This past August, we released our latest PAC, which runs a Linux real-time operating system (RTOS) and lets users save on development time by leveraging open-source code."

About the Author

Jim Montague | Executive Editor, Control

Jim Montague is executive editor of Control. He can be contacted at [email protected].

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