AUMA FQM 05.1 - Page 31

ESD safety function with PVST
Table 6: Safety instrumented figures and failure rates according to IEC 61508-2:
2010
Key performance indicators
1)
Fault category
0λ
SD
273 FITλ
SU
784 FITλ
DD
513 FITλ
DU
67 %SFF
2)
60 %DC
95 %PTC
SIL2 (HFT = 0), SIL3 (HFT = 1)SIL AC
3)
3.92E-03PFD(T
Proof
) = 1 year
8.19E-03PFD(T
Proof
) = 3 years
1.25E-02PFD(T
Proof
) = 5 years
The analysis was performed assuming that PVST faults can be detected by monitoring the end
position switch via a safety PLC.
1)
To determine the overall SFF (safe failure fraction), the overall final sub-system must be evaluated.
The indicated figure is for reference only.
2)
SIL AC (architectural restrictions) means, that the calculated values are within the range for hardware
architecture restrictions of the respective SIL.
3)
Safe end position with PVST safety function
The safety figures in the tables below refer to an end position feedback (i.e. either
end position OPEN or end position CLOSED). If the end position feedback of both
end positions OPEN and CLOSED are to be considered, the indicated safety figures
must be considered once for each of the two end positions.
Table 7: Safety figures and failure rates according to IEC 61508-2:2010 for feedback
of one end position (OPEN or CLOSED) with PVST
Key performance indicators
1)
Fault category
0λ
SD
0λ
SU
103 FITλ
DD
42 FITλ
DU
71 %SFF
2)
71 %DC
95 %PTC
SIL2SIL AC
3.52E-04PFD(T
Proof
) = 1 year
7.01E-04PFD(T
Proof
) = 3 years
1.05E-03PFD(T
Proof
) = 5 years
The analysis was performed assuming that PVST faults can be detected by monitoring the end
position switch via a safety PLC.
1)
To determine the overall SFF (safe failure fraction), the overall final sub-system must be evaluated.
The indicated figure is for reference only.
2)
31
with non safety-related actuators Safety-related figures