Siemens SIPART PS2 Operating Instructions Manual page 141

Description
The following table shows the dependency of the SIL on the "average probability of dangerous
failures of a safety function of the entire safety-instrumented system" (PFD
with "Low demand mode", i.e. the safety function is required a maximum of once per year on
average.
Table 8-1
The "average probability of dangerous failures of the entire safety-instrumented system"
(PFD
Figure 8-2
The following table shows the achievable Safety Integrity Level (SIL) for the entire safety-
instrumented system for type A devices depending on the safe failure fraction (SFF) and the
hardware fault tolerance (HFT).
● Type A devices include analog transmitters and shut-off valves without complex
● The specific values for your device are listed in the manufacturer's declaration (SIL
SFF
< 60%
60 to 90 %
90 to 99 %
> 99%
SIPART PS2 with PROFIBUS PA
Operating Instructions, 02/2016, A5E00127926-AB
Safety Integrity Level
SIL Interval
4 10 ≤ PFD
-5
3 10 ≤ PFD
-4
2 10 ≤ PFD
-3
1 10 ≤ PFD
-2
) is normally split between the following three components:
AVG
PFD distribution
components, e.g. microprocessors (see also IEC 61508, Section 2).
Declaration of Conformity, Functional Safety according to IEC 61508 and IEC 61511):
Certificates (http://www.siemens.com/processinstrumentation/certificates).
HFT for type A devices
0
SIL 1
SIL 2
SIL 3
SIL 3
< 10
-4
AVG
< 10
-3
AVG
< 10
-2
AVG
< 10
-1
AVG
1
SIL 2
SIL 3
SIL 4
SIL 4
Functional safety
8.3 Safety Integrity Level (SIL)
). The table deals
AVG
2
SIL 3
SIL 4
SIL 4
SIL 4
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