Analysis: PLCs in the classroom and in the field

While visiting a plant recently, Thomas R. Kurfess, Ph.D., P.E., sat in on a discussion related to the future of programmable logic controllers (PLCs).
By Control Engineering Staff December 13, 2007

While visiting a plant recently, Thomas R. Kurfess, Ph.D., P.E., sat in on a discussion related to the future of programmable logic controllers (PLCs). The plant was upgrading, and trying to decide if it would replace its aging PLCs with newer versions, or upgrade completely to programmable automation controllers (PACs). The argument for the PLCs was quite good, Kurfess says.
“Basically, replacing the old PLCs with new ones permits the code (written in ladder logic) to be easily ported. The plant personnel are quite familiar with the PLCs and the ladder logic. Also, the PLC is a robust and well proven technology.”
The big problem with the PLC,” Kurfess continues, is that “it is fairly expensive, and ladder logic can get fairly complicated and messy when trying to do some advanced programming. In fact, ladder logic is not a particularly popular topic in the classroom.” Kurfess is BMW Chair of Manufacturing at Clemson University’s International Center for Automotive Research, and a columnist with Control Engineering magazine
In general, says Kurfess, “ladder logic is difficult to teach and difficult to learn. Many newer graphically oriented products are now available that are much more user friendly and intuitive, making them preferred buy both instructors and students alike. Fortunately, many of these are compilers that generate ladder logic from user input, which allows them to be used with PLC hardware.”
So, will the PAC replace the PLC and the factory hardened computer, we asked? “I like to think about the PAC taking the same path that the PC has in our homes and offices. Like the PC, the PAC has the potential to replace a number of systems. The PC, for example, has replaced any specialized word processing hardware with a few exceptions. I still do see a few typewriters around, but they typically cost more than a PC. The PC also could replace CD players, DVD players and telephones. The same can be said for the PACs. They will grab some of the PLC market share, but not all of it.”
Find more on this and related topics by searching “Kurfess” atop www.controleng.com.

–Renee Robbins, Control Engineering News Desk, renee.robbins@reedbusiness.com