[Kelbit]

True to a point.

The difficulty arises when trying to implement something in ladder that is too complex for simple Boolean operations, and would probably be much clearer if written in a few dozen lines of Structured Text (assuming an IEC 61131-3 PLC). Unfortunately, company policies (especially in North America) mean that engineers are often forced to use ladder, resulting in a ladder logic program which is inscrutable for both the electrician and the engineer.

What would be sensible is using the right tool for the job: ladder for simple Boolean operations, and ST for more complicated stuff. Tech schools should also teach electricians and technologists the basics of how to read structured text - they do this in Europe, but I don't think it's common in North America yet.

[snowwindwaves]

I use ladder only on Allen Bradley PLCs and then only for primarily boolean logic. the AB ladder editor is much better than their function block editor.

Generally I prefer function block, especially in Schneider's Unity, since I find it is easy to watch a process operate the way function block diagrams are animated. The function block also promotes code re-use by creating your own blocks.

I use structured text only when the problem can't be well represented in function block, or more like I haven't figured out how to well represent it in function block yet. It is much harder to observe the operation of ST as the tag values aren't animated. Of course you can't use breakpoints on a process without stopping it, which usually you don't want to.

[karmicthreat]

The company I work for is at the inscrutable ladder logic point. If our PLC engineer dropped dead, nobody would be able to pickup and go. I would be at least a month or two of software archeology for someone to come in and take over.