Bill Wheeler

I'm a new member and have been in the same boat. I recommend that you brush up a bit by reading through ISA standard 5.1 through 5.4. These documents can be found without too much problem. In any case a P&ID can never by itself give much detail as to the control logic. It can only define the ins and outs of a process. What I have found that works for me is to document the logic in the simplest form, a flow chart. I then create a document link name to the specific logic segment flow chart (i.e. L3.1 - Logic diagram 3, segment 1) and include that name in a diamond symbol on the P&ID. ISA 5.3 (I think) does a good job in defining binary control logic diagrams, but fails to provide a method for documenting more complex integer variable process controls where as a flow chart can be used very easy. Once in flow chart form, the logic can be created very easilyis very easy Standards are a good way to start, but todays controllers far exceed those available at the times the standards were written.