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Competence in Functional Safety
Functional safety of globe valves, rotary plug valves, ball valves and butterfly valves
Abbreviation Designation Description
MooN Voting “M out of N“ (e. g. 2oo3) Classification and description of the safety-related system regarding redun-
dancy and the selection procedure used.
• “N“ indicates how often the safety function is carried out (redundancy).
• “M“ determines how many channels must work properly.
Example: Pressure measurement in 1oo2 architecture
A safety-instrumented system decides that a specified pressure limit has
been exceeded if one of two pressure sensors reaches this limit. In a 1oo1
architecture, there is only one pressure sensor.
MooND Voting “M out of N“ with diagnostics
Relevant standards
Norm Designation
IEC 61508
Parts 1 to 7
Functional safety of electrical/electronic/pro-
grammable electronic safety-related systems
IEC 61511
Parts 1 to 3
Functional safety – Safety instrumented systems
for the process industry sector
VDI 2180
Parts 1 to 5
Safeguarding of industrial process plants by
means of process control engineering
Terms and definitions
Term Definition
Dangerous failure Failure with the potential to set the safety-related system to a dangerous or inoperative state.
Safety-related system A safety-related system carries out the safety functions needed to establish or maintain a safe state,
e.g. in a plant.
Example: Pressure measuring instrument, logic unit (e.g. limit switch) and valve form a safety-related system.
Safety function A defined function carried out by a safety-related system in order to establish or maintain a safe state of
the plant, under consideration of a specified dangerous incident.
Example: Pressure limit monitoring
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