Definition:
Logic Diagrams graphically represent the logic implemented in a safety logic solver to perform specific safety actions. It uses a certain type of logic per IEEE, ISA, or IEC.
Key Points:
- Often use function blocks, ladder diagrams, or Boolean expressions.
- Used to document safety logic in SRS.
- Some simple facilities do not use logic diagrams and use a combination of a MIL and a Functional Narrative.
Example:
An FBD showing that two out of three pressure sensors must trip to close a shutdown valve.
See also: Functional Narrative, Main Interlock List (MIL)
Cited Source:
- IEC 61131-3.