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For most facilities, PCNs are available from a previous process control software upgrade or a project that expanded or built the process or facility. This provides a starting point for reviewing and updating the PCN for a new project that will change the process or software. If a PCN is not available, the process description or a document from a similar process or facility can be used as a basis for the PCN.

During a change in the software or process, the PCN will be updated in parallel to the P&IDs as the process is defined and new monitoring and control elements are introduced. During this process, flow charts, equipment operation tables, and control descriptions will undergo many iterations. Once these changes are complete, alarms, setpoints, and performance data should be finalized.

Following a change to the process or upgrade to the software, changes may be made to the operating parameters of the system. These changes to alarm limits, setpoints, and KPIs should be updated in PCNs to keep the document up to date as an operator reference, training tool, and base document for future upgrades.