Definition:
A Functional Narrative, also called a Functional Description (and perhaps other things), is a detailed written explanation of how a process, system, or Safety Instrumented Function (SIF) operates under different conditions. It can be one of the primary design inputs to the programming effort.
The functional narrative, main interlock list (MIL), and the logic diagrams together comprise the primary design inputs to the programming effort.
Key Points:
- Describes normal operation, shutdown sequences, alarms, interlocks, and emergency conditions.
- Bridges the gap between process design and control system programming.
- Relates to the MIL, logic diagrams, and application programming.
Example:
A functional narrative details how a high-high level in a separator vessel triggers an alarm, initiates shutdown, and closes inlet valves in sequence.
See Also: MIL, logic diagrams
Cited Source:
- ISA-84.00.01:2004 – Implementation Guidelines.
- Excellent article on LinkedIn – Cornerstone of Successful Automation