Voting (MooN) annotation
ISA 5.1-2009/2022 (general instrument and function symbols) / IEC 61511
Drawn as
Text such as 1oo2, 2oo2 or 2oo3 written beside the signal lines where two or more measurements join into one alarm, trip or SIS function.
Meaning
M-out-of-N voting: 1oo2 trips when either of two sensors trips (safe, more spurious trips); 2oo2 needs both; 2oo3 needs any two of three. It tells you how many field sensors exist: model N of them. Logic only, nothing physical beyond the sensors.
Variants
- Some legends put the voting inside the logic box (e.g. UZ 2oo3)
- F&G uses the same notation for detector voting (2ooN confirmed gas or fire)
Not physical hardware. Read it, then skip it in the 3D model.