Announcing: Patterns of Ladder Logic Programming

You may have noticed I recently added a new section to this site: Patterns of Ladder Logic Programming. My goal, as usual, is to try to help new ladder logic programmers come up to speed faster and without all the trial and error I had to go through.

The new Patterns section is an attempt to distill ladder logic programs into their component parts. I assume the reader already knows the basic elements of ladder logic programming, such as contacts, coils, timers, counters, and one-shots. The patterns describe ways of combining these elements into larger patterns that you’re likely to see when you look through real programs. In my experience, you can program 80% of the machines out there by combining these patterns in applicable ways.

The Patterns section isn’t complete yet, but I will be adding to it slowly over time. If you think of a pattern that’s blatantly missing, please send me a note so I can include it.

2 thoughts on “Announcing: Patterns of Ladder Logic Programming

  1. Andy Janish

    I wish I had found your site before we upgraded our plant control system from a legacy Honeywell DCS to Rockwell PlantPAx with a ControlLogix PLC. I was learning everything on the fly and would have benefited greatly from the standardized patterns of code and file structure on your site. I’m redoing a lot of work now to get everything better organized and rewritten.

    That being said, do you have any suggestions for additional resources on PLC design methodologies and/or best practices? I’m trying to put together a set of guidelines for our plant and so far most of it is based off of your website.

  2. Scott Whitlock Post author

    @AndyJanish – actually most of what I’ve written is just stuff I’ve picked up from other PLC programmers over the years, and stuff I’ve figured out myself through trial and error. I don’t have any formal training in ladder logic or PLC programming. I haven’t read any books on the subject. I did read an introductory tutorial once (I think at and it’s good, but it focuses on how a PLC works, but not so much on programming patterns and best practices. If you do find other similar information online, I would appreciate it if you’d send it to me or post it. I would like to include links to other similar information.


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