Reader Feedback: So Long Windows, Ladder Logic Too?

Feb. 12, 2014
Our Reader Discusses Why Ladder Can Do Discrete Logic Better Than Any Other Method of Visualization

Linux might make some inroads in the control world against Windows and good riddance (see our October 2013 issue cover story, "Old Skills, New Skills"). But the problem that stands in the way of extensive selection of Linux or any Linux-based hardware is one of control and version standardization.

Today, one can buy a Windows version or, I suppose, an iOS version, and be very confident that the behavior of that OS is (reasonably) well-documented and very predictable down to the level of fine details.

SEE ALSO: Control Your Programming Language

But Linux, on the other hand, even a specific Linux version, is not really one OS. It is a hundred OS versions that have been tinkered with and tweaked by numerous people and organizations with little or any documentation. Fine for the small operator who is building one-off products or systems, but anathema for any large system or one that has to be able to be redeployed again and again over several years.

And as far as ladder logic is concerned, it will be with us for a long time to come. There is simply no other method of depicting logic that is so intuitively easy to understand and so little subject to interpretation about the fine details of the function of each element. There are a lot more maintenance people who can follow a ladder diagram than there are those who can understand SL or FBD. In addition, it’s much easier to follow the signal flow when online monitoring a program in ladder logic than in SL or FBD. The other programming languages have gained popularity as more and more number crunching applications are being ported to PLCs and PACs, and as the programmers who write programming software discover that it’s easier to put a complex analog function into FBD or SL format than it is to turn that function into a ladder element. Bottom line: ladder can do discrete logic better than any other method of visualization and can support complex function blocks, while the other languages have problems with visualization. They may handle analog better than ladder (arguable), but they are much more troublesome for discrete logic.

Kim Ground,
Senior EE - Controls
Surface Finishing Technologies,