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October23,2016|Slide17
Hardware Fault Tolerance using SFF in BS EN 61511
Ed 1
§
Applies to PE Logic Solvers
§
The ‘cleverer’ the PES, the less fault tolerance required for the
target SIL
SIL
Minimum Hardware Fault Tolerance
SFF < 60% SFF 60% to 90% SFF > 90%
1
1
0
0
2
2
1
0
3
3
2
1
4
Special requirements apply (see BS EN 61508)
BS EN 61511-1 Ed 1 Table 5
Using SFF for sensors refers you to BS EN 61508
§
61511-1 Ed 1 Clause 11.4 - Requirements for Hardware
Fault Tolerance
§
11.4.5 Alternative fault tolerance requirements may be
used providing an assessment is made in accordance
to the requirements of IEC 61508-2, Tables 2 and 3.
©ABBGroup
October23,2016|Slide18