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Slide 19
InstMC FS2016 V1.3
Nicol Instrument Engineering Limited
Hardware Fault tolerance (HFT)
Edition 2.0 simplifies the basic HFT requirements, but
still allows choosing from more complicated
paths……. Table 6 is based on IEC 61508-2 route 2H.
HFT is a separate design requirement in addition to
PFD/PFH, and applies to each SIF.
Can be evaluated at SIS sub-system.
DC for FVL or LVL programmable devices not < 60%.
SIL
Minimum HFT
1 (Any mode)
0
2 (Low demand mode)
0
2 (High or continuous demand mode)
1
3 (Any mode)
1
4 (Any mode)
2