Logic diagrams and equivalent cause and effect or event diagrams, should be produced for all applications where instrument equipment performs logic functions. Logic diagrams should be separated from P&IDs.
Logic diagrams should show the interlocking and sequencing of switching systems for the start-up, operation, and shutdown of equipment and processes.
Logic diagrams should be drawn using the symbols shown in International Standard of Automation (ISA 5.2).
Logic diagrams show the flow of information and do not imply the type of equipment to be used to implement them. Implementation may be by programmable logic controller, relay logic, computer, or a combination of any of these.