There are several pieces of software that are used by engineers writing Requirements Specifications, including:
Office software for words and spreadsheets
Visio and AutoCad are often used for P&ID's and loop diagrams and even logic diagrams.
Visio is able to produce pretty pictures but is too general purpose, has no idea about control, apart from a few graphic libraries, and does little on the data side without a huge effort.
Document management systems help keep control of versions
Spec-Soft PFS Suite is intended to facilitate the engineering activities involved in automation software by leveraging the P&ID.
You may think UML Modeling tools are relevant - but they do not help with process automation in our opinion.
SFCEdit (now embedded in ControlDraw) is a tool for drawing Sequential Function Charts, also known as Grafcet
Wouldn't it be great if there was some software that could do all the various documents you need to produce, handle versions properly and kept it all together?
There is, it is called ControlDraw
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