During plant development the process engineers specify the process through the development of the P&IDs (Piping & Instrument Diagram). Throughout this effort, the process engineers depict the total plant behavior. However, the P&IDs provide limited facilities for documentation of the overall functionality and operational aspects of the plant.
It’s the control system engineer’s task to design the control system to fulfill the process functionality required to achieve product specifications as well as the requirements imposed by the overall operating & control philosophy and manning levels. The operator’s understanding of the operational efficiency of the plant is a difficult task without proper documentation of the overall control and monitoring functions available.
Often, operational problems within the different systems cannot be identified until the system is in operation, leading to major modifications in late project phases. In order to get a common understanding of control system functionality between all involved parties at an early project stage, System Control Diagrams have been introduced.