PLC program logic or block diagram creation and standard symbol set

Is there an ISA or IEEE standard which details symbols that one would use to create a logic diagram representing the PLC program?


I only have a few diagrams that are mostly the same project to project; one detailing the SFC state machine, one detailing a governor so it is just a block diagram of the transfer function essentially, and another that is essentially a print out of a matlab simulink model so it is mostly squares with different labels on them and some summing junctions.

On a couple I've created diagrams illustrating a series ESELs or MUXes and min/max blocks with multiple inputs so people can see what input is going to end up at the output, and one with a series of AND and OR gates which was kind of a pain.



How often or for what percentage of the program does everyone create drawings that detail how the program works?



I haven't found any good examples or standard documents. Does anyone know of one?


Thanks

Are you looking for something like IEEE Std 91?

A lot depends on the audience for the documentation. If I'm writting for other EE's or PLC programers the code itself should suffice for a drawing just add accompanying text.

A wider audience requires more simplification. But even then I've had questions about what logic gates are and the like from ME's.

And if you are writing for a civilian (like a manager) just use a big box labeled 'dark magic occurs here'.

IEEE 91 doesn't seem to contain things like timers that are part of a PLC program. It's more about electric circuits.



ISA S5.1 seems to be more about the instruments and process than the contents of the program.