At an OEM I used to work for, my mechanical counterpart would always write a "Process Description" for our systems that were used in the bid proposal stage and once contract was awarded they became part of the O & M manual. I devleoped my controls schemes and wrote my PLC code using this document. It would include the follwing:
Overview of the equipment, including normal operating parameters, modes and explanation of system components.
Detailed description of each subsystem (i.e. Feed/Storage Tank, Reject, Permeate, Clean-In-Place, etc.). This would include all system components such as pumps, control valves, instrumentation, etc.
Description of operating modes and discussion of controls used for operation, setpoints, etc.
Operating procedures for all modes of operation.
All alarms, alarm setpoints, effect of each alarm on machine operation, corrective action for each.
Peppered throughout the document, any reference to a control or instrument called it by name, followed by its ISA loop number in parenthesis. Example: Feed Pump (PP-1) HMI Start Pushbutton (PB-5001AA).
List of all process instruments and their calibrated ranges.
Drawing list.
Hope this helps!
