By Mike Bacidore, Managing Editor
Over the past decade, PC-based controls and dedicated controllers have had their comparative advantages and disadvantages scrutinized by almost every controls engineer. 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—has 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 I wanted to ask real people what they thought. The responses were so overwhelming, that not all were include in the print version of this article, but here you'll find all of them. Scroll down and read the opinions of all the machine builders, system integrators and automation suppliers who responded.
Talon Manufacturing (www.talonmfg.com) in Spring Park, Minn., is a supplier of bagging systems for microwave popcorn and other snack food and last year undertook a controls upgrade from traditional rack-mount PLCs to PC-based controls.
“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.”
Hohn says the embedded PC’s direct connection to input/output terminals and the use of Windows XP providing helpful tools from the office for use on machines also contributed to the selection.
“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,” recalls John H. Lewis, PE, vice president of engineering and construction, Fulghum Industries, a Wadley, Ga., builder of woodyard systems. “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.”
PLCs will always have their place, says Kyle Knoff, R & D team leader—electronics at GEA WestfaliaSurge’s Farm Technologies Division in Galesville, Wis., 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,” he says. “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, says Knoff, 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,” he explains. “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.”
Rodney Price, senior electrical engineering specialist at Belvac Production Machinery, a beverage canmaker in Lynchburg, Va., has already made the change. “I am in the process of switching to PC-based controls right now,” he says. “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.”
“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.”