Basically, the ISA guys have defined a standard for Engineering Logic Diagrams that is world widely used. PLC programmers and Automation engineers are familiar with this diagrams the most used tool for draw this is AUTOCAD.
There is not open source tool that support this drawings, I think dia could do the job. This a link to the standard. And I have may examples to send, I don't know is possible to post pdfs files on the list.
Hello, I would like to help develop DIA for supporting ISA Logical Diagrams. I'm not sure about the copy right of ISA's symbols. I'm not sure were I should start.