PC-Based Controls or Dedicated Controller?

May 1, 2009
Over the past decade, PC-based controls and dedicated controllers have had their comparative advantages and disadvantages scrutinized. We recently surveyed our readers, asking who has switched control preferences of late, and contrary to what some might have expected, our report indicates that the biggest change - almost one-third - as been from PLC to PAC, defined by most of those same respondents as a hybrid controller with PLC and PC capabilities that integrates motion and data acquisition with control and monitoring. And yet a select few - almost 8% - admitted changing platforms to PC.

Over the past decade, PC-based controls and dedicated controllers have had their comparative advantages and disadvantages scrutinized. We recently surveyed our readers, asking who has switched control preferences of late, and contrary to what some might have expected, our report indicates that the biggest change - almost one-third - as been from PLC to PAC, defined by most of those same respondents as a hybrid controller with PLC and PC capabilities that integrates motion and data acquisition with control and monitoring. And yet a select few - almost 8% - admitted changing platforms to PC.

Survey data is nice, but here's what some actual engineers had to say.

“We selected an embedded PC largely due to its small-housing format,” says Dennis Hohn, Talon’s president. "Its design as a high-end industrial PC that fits on the DIN rail became a major space-saver for us when compared with the old PLCs.”
—Dennis Hohn, president, Talon Manufacturing, Spring Park, Minn.

“My first controller was a TRS-80 Model I with 16 kb total memory and a ribbon cable expansion box with transistor solid-state switching and Analog Devices’ A/D and D/A chipsets. This dedicated architecture has evolved into today’s PAC and PLC controllers. Today's PCs are fast and economical, but they lack the industrial strength and dedication of a PAC; the use of a PC in a controller application involves an emulation, which is another level to slow the process and allow glitches or failure. The mandate for the controller manufacturers is to keep up with PC processor speed and bandwidth to provide the most dependable and fastest dedicated equipment. Everything else is I/O or software.”
—John H. Lewis, PE, vice president of engineering and construction, Fulghum Industries (www.fulghum.com), Wadley, Ga.

“PLCs will always have their place, especially for short-run or low-volume projects. We design printed circuit boards (PCBs) for most of our large-volume control projects—more than 1,000 per year—and some low-volume—less than 100 per year. However, we find the PCB suppliers would like to drop the low volume, although recently with the economic downturn this trend has changed. The PLCs, PACs and CNCs all have the distinct advantage of being flexible due to programming ease. The PC control side is making a lot of headway into the PLC side of controls, but the real issue becomes support. In the early ’80s, we used PCs to control 8088s. After 10 years, it became impossible to make sure we had PCs that would run the old software correctly. As much as we would like to think old PCs are available, they have been a lot harder to support than old PCBs or PLCs. We have 25-year-old PCBs we can still manufacture consistently with minimum updates to components. Maybe it is our industry, but we receive phone calls daily on milk pumps and controls that were designed in the ’70s, and the dairymen expect replacement parts as if the product had been purchased yesterday. I know I have serviced 20+-year-old PLC installations with no problems locating parts. If you can find a PC controls supplier that gives you a 20-year service life, then PCs will win. Until then, PLCs and PCBs will continue going strong. Good luck to those that went to PC control. They will have a rough road ahead. I do believe the future could be different. As more PCs are adopted as a control platform, more industrialized PC hardware and software suppliers will surface.”
—Kyle Knoff, R & D team leader—electronics, GEA WestfaliaSurge’s Farm Technologies Division (www.westfaliasurge.com), Galesville, Wis.,

“I am in the process of switching to PC-based controls right now. I was using a PLC, but the scan time was too long to capture the inputs I needed, so I’m now replacing it with a Beckhoff PC that’s faster, better and cheaper.  To me, PLCs have been very important, but their day has come, and now the PC is stepping up to do the job.”
—Rodney Price, senior electrical engineering specialist, Belvac Production Machinery (www.belvac.com), Lynchburg, Va.

“I design custom controls, and what I see is the continuous erosion in the ability of our customers to handle technology. The simpler the better, and ladder logic and programming makes life pretty tough to the non-skilled. In a nutshell, PC-based controls can be quite easy to work with since you have such a media-rich programming environment. A high-resolution monitor beats a little LCD any day to help people understand their programming and controls task. The interesting thing is that PC-based boards from say National Instruments are powerful but come with a lot of background overhead with .exe files running. I see the future as a mix. PC-based, programmed and controlled controllers. If a single-board solution works, it’s easier for customers to do with the rich Windows OS. If it’s industrial, then it requires a hybrid of control/PC. If it’s simple and repetitive, then maybe the pure PLC. There is no black-and-white answer, but the full-size touchscreen monitor should be the purveyor in the end, as costs come down and touchscreens look like big screens.”
—Adam Suchko, chief engineer, Engineering Concepts (www.ecu-engine-controls.com), Fishers, Ind.

“While PC-based control is certainly an important part of automation systems, it was not designed to be a replacement for PLCs, PACs or CNCs. PC-based control is intended to bring very close integration between automation controllers and the openness of a PC platform mainly for applications that need this. The real trend is to improve the robustness of PC-based control by making it targetable for both PC or embedded platforms, combining the power and openness of PC functionality with the ruggedness of a PLC.”
—Eric Kaczor, product manager, discrete automation, Siemens Energy & Automation (www.usa.siemens.com)

“I work for an OEM and our customers remain committed to PLCs. I think eventually they will migrate, but PLCs are fairly robust, and the maintenance guys like them.”
—Joseph Heil, controls designer, Tann (www.tanncorporation.com), Kaukauna, Wis.

“While PCs will continue to be used in control applications, there are key reasons why they will not be able to replace PLCs or PACs. With the capability to provide high-speed processing, true CPU redundancy and multiple microprocessors for logic solving, math co-processing and communications, PLCs and PACs are dedicated to the applications they are implemented to control. Their operating systems and firmware can be optimized for specific performance without concern for the compromises imposed on PCs by the many other programs that may be installed on them. It is also much more cost-effective to implement distributed control by using multiple PLCs/PACs to each control a portion of an application. It is not cost-effective to implement distributed control using PCs.”
—Stephen L. Arnold, U.S. automation product marketing, PLC hardware, software and communications, Schneider Electric (https://www.se.com/us/en/)

“The line between PLCs, PACs. CNCs, DCSs and embedded computer controls will continue to blur, and features offered will continue to increase, but Windows-based PC controls will never replace any of the dedicated controllers for reliability, maintainability and cost reasons.”
—Cindy Hollenbeck, VP, SoftPLC (www.softplc.com)

“Since all of these control classifications are all really CPU-based systems, it’s hard to discriminate. However, the underlying difference is the operating system. PLCs, PACs and their ilk invariably operate on proprietary operating systems, whereas so-called PC-based control operates on Windows or some similar open-source platform. Some have been offered with a Linux OS. The issue, herein, then becomes which system can really run machines and processes in real-time. Proprietary systems tend to be slower, requiring additional hardware modules with specific firmware to operate in real-time, like a motion-control module. Some even go to the extent of distributing the motion and high speed I/O, depending on a fieldbus network of some sort to interface. The latter takes the burden off the central CPU running the proprietary OS. What is compelling about PC-based control is that many packages come with high determinism through a real-time extension or use CE 6.0—the latter being deterministic down to 1 ms. That allows one package—like a touchscreen packaged with a CPU motherboard that includes all the connectivity—to offer multiple-function platforms, all in software and user-configurable. These packages offer the entire machine-control functionality:
1. OIT through the TS
2. HMI through software
3. SCADA software
4. Real-time PID software
5. IEC-compliant PLC is software
6. Soft motion control
7. Networking through multiple ports—serial, Modbus/TCP, Ethernet.
All this in one package is far less expensive and far more functional than the brand PACs.”
—Loren Shaum, principal, COMTEC, Syracuse, Ind.

“I think the PLC has a long-standing solid track record. The PC is not going to take the place of the PLC anytime soon. PACs are too new; however, they could find their place in higher-end motion control or network applications.”
—Rick Simer, motion control product engineer, SEW-Eurodrive (www.seweurodrive.com)

"PACs give engineers the power and flexibility of PC-based control while still being as reliable as a PLC. While PLCs and CNCs will continue to have their place, engineers complement their systems with PACs and use PACs as a way to bring in PC-based control without sacrificing on the reliability."
—Arun Veeramani, product manager, LabView industrial software, at National Instruments (www.ni.com)

“There is a place for both, but we don't see PCs taking over as PLCs and high-end CNC controls continue to improve. The type of PLCs Sunnen uses fit the specific task at hand for the right price. Likewise, the power and expense is justified in the industrial PCs Sunnen uses on our more complex equipment. For our particular application, the alteration of software for sequencing motion, and the motion itself, necessitates the PC.”
—Russ Jacobsmeyer, chief technology officer, and Mike Nikrant, R&D engineer, engineered machines and custom systems group, Sunnen Products (www.sunnen.com), St. Louis

“Yes, PC-based control will continue to replace PLCs in some applications where data collection and PC-based integrated tools are important. But the PLC will never go away because of its rock-solid dedicated operating system and performance.”
—Greg Peterson, national sales manager, Exor (www.exor-rd.com)

“PC-based controllers will replace PLC and PAC systems because PC-based controls have several advantages, including a screen, expansion modules for stepper motor controllers and serial interfaces, lower cost and the opportunity to create your own software.”
—Maichel Gerges, electrical section manager, Santamora Egypt for Blankets, Cairo, Egypt

“Programmable automation controllers have greatly minimized the niche of PC control. Most PACs, like GE Fanuc's PACSystems, are based on the latest off-the-shelf technology that provides users the performance, flexibility and multi-discipline control they require for diverse applications. They provide all of the benefits of PC control but with the extra added benefits of real-time connectivity and integration that can greatly simplify production processes and pay major dividends for the business overall. PACs are the future of control technology.”
—Bill Black, controllers product manager, GE Fanuc Intelligent Platforms

“It’s common sense that anything that needs to be protected can’t be an open system. And who needs that power and flexibility for a system which has to be programmed to be doing the same thing for almost its whole life; it needs reliability. If the PC isn’t running on Windows, I wouldn’t mind using PC-based controllers. However, I would prefer dedicated controllers or PLCs.”
—Arunkumar Srinivasulu, project engineer, LogiCamms (http://www.logicamms.com.au/), Perth, Western Australia

“PC-based controls do not have operating systems designed and dedicated to providing uninterrupted real-time control. Further, they share their resources between applications and system activities. Some of these activities are under user control, and some are not. This affects the speed and repeatability of operation and is outside of the control of the user. Even the best-written soft control program is at the mercy of the operating system that the PC utilizes. PLCs are not only designed to run under normal conditions, they are also designed such that when they fail, the output states are predictable. When a PC freezes or experiences hard drive failure, there is often no telling what might happen to the I/O. PCs are not scalable the way PLCs are, to balance price vs. performance. Small PLCs will continue to be a better value for small stand-alone applications and for high-speed distributed control applications.”
—Mike Foley, product manager, programmable logic products, Eaton (www.eaton.com)

“I don’t think it will be for a long while because of PC boot time and operating system crashes. PLCs are more robust and less expensive.”
—Art Krallman, controls engineer, Lomar Machine & Tool (www.lomar.com), Horton, Mich.

“PC-based controls will replace some PLCs, PACs or CNCs. In fact they have done so already. The real decision point is the need to have an integrated HMI/controller that a PC-based system can provide. This has a very good following in the CNC world. In factory automation, it is a different story. Sometimes the low-cost PC or lower-cost PAC is preferred due the nature of the application need. In other words, you don't want to use a $3,000 PC-based controller when a $250 PLC will do the job. Lastly in motion control, a PAC can offer advantages in size and speed and in some cases cost over a PC-based controller.”
—Andy Urda, director, corporate marketing, Yaskawa Electric (www.yaskawa.com)

“PCs are not going to replace PLCs or PACs anytime soon. There are far too many applications that require a physically small and hardened solution in both hardware and software. My iPod can play music and videos. My computer can play music and videos, I am not going to replace either with either. They both have their places. One is not exclusive of the other. You cannot set up and program a PLC/PAC without the PC. The PC is the best way to view and examine data from the PLC/PAC. Despite the advances we have seen in the Netbook type computers, they are simply not small enough, robust enough or low-power enough to replace the PLC/PAC.”
—Ben Orchard, application engineer, Opto 22 (www.opto22.com)

“PCs will never completely replace PLCs. PCs carry around too much overhead just to be a PC, and boot times for a PC alone mean PLCs will always have an advantage.”
—TJ McDermott, senior project engineer, Formost Fuji (www.formostfuji.com), Woodinville, Wash.

"Due to the tools, comfort and knowledge programmers have with the PC environment, the ease and standardization of networking with Ethernet and the availability of low-cost remote-IO/PLCs and advanced easy-to-use motion controllers, there is no longer the need for expensive, dedicated PLCs and CNC controllers."
—Wayne Baron, president of Galil Motion Control (www.galilmc.com)

“PLCs, PACs and CNCs are dedicated to the job and are highly scalable and decentralized both functionally and geographically. PC-based control is centralized and nonscalable. If PC-based control is replacing them, then once again one has to make quantum changes in the PC architecture, and eventually it will become PLC.”
—Subhabrata Bose, control & instrumentation engineer, Hydrogen Power Abu Dhabi Project, Masdar, Abu Dhabi, United Arab Emirates

“Service life and support are key reasons PC-based controls will not replace PLCs, PACs or CNCs on industrial machinery. Compared to PC-based controls that constantly change due to processor upgrades every one or two years and frequent software version upgrades, the PLCs, PACs and CNCs are intended to have a long life—10 to 30 years—be available for purchase and support—15 to 20 years—and have software upgrades that retain familiar functionality. Future controllers will be small, modular and powerful; are programmed using all IEC 61131-3 languages; and offer wireless communications as a standard feature for programming, monitoring and non-critical I/O, process and motion applications.”
—Rich Jackson, senior product marketing manager, mid/large PLCs & temperature controllers, Omron Electronics (www.omron247.com)

“PCs generally are not industrially hardened units and are made to be ‘throw away,’ which doesn’t lend itself to industrial automation and controls. Most PLCs, PACs and CNCs are designed for long-term use, and some units will be in service for 10-15 years.
—David J. Woodson, instrumentation specialist, Alliance Engineering, a Wood Group company, Houston

“I think that PC-based controls or higher-level controllers will eventually replace PLCs and PACs, but not until they can prove their reliability like a PLC. I don't see this happening in the near future. At this point, PLCs and PACs are simpler, less expensive, more mainstream and more reliable.”
—Rob Stevenson, motion control product engineer, SEW-Eurodrive (www.seweurodrive.com)

“PC-based?  Why? I have to be able to manage many valves, phases and sequences and able to track information and history. And one main issue is that code can be very complicated.”
—Monika Hayward, process engineer, dipl. brewer, MillerCoors (www.millercoors.com), Elkton, Va.

About the Author

Mike Bacidore | Editor in Chief

Mike Bacidore is chief editor of Control Design and has been an integral part of the Endeavor Business Media editorial team since 2007. Previously, he was editorial director at Hughes Communications and a portfolio manager of the human resources and labor law areas at Wolters Kluwer. Bacidore holds a BA from the University of Illinois and an MBA from Lake Forest Graduate School of Management. He is an award-winning columnist, earning multiple regional and national awards from the American Society of Business Publication Editors. He may be reached at [email protected] 

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