576 / 1143
7
©ABBGroup
October23,2016|Slide13
Hardware Fault Tolerance using BS EN 61511-1 Ed 1
BS EN 61511-1 Ed 1 Table 6
SIL 2 Logic
Solver
SOV Trip Valve
Level
SIL
Minimum hardware fault tolerance for sensors, non-
programmable logic solvers and final elements
1
0
2
1
3
2
4
Special requirements apply (see BS EN 61508)
Hardware Fault Tolerance using BS EN 61511-1 Ed 1
§
This shows for target SIL 2, a HFT of 1 is required
§
This means two sensors are required
§
This is the traditional method of dealing with high levels
of risk reduction
©ABBGroup
October23,2016|Slide14
SIL 2 Logic
Solver
SOV Trip Valve
SOV Trip Valve
Level
Level
OR
OR