9 determining the safety integrity level (sil), Determining the safety integrity level (sil), 6 safety manual – JUMO 701150 14597 safetyM STB/STW - Safety Temperature Limiter and Safety Temperature Monitor Operating Manual User Manual
Page 43
6 Safety Manual
43
6.9
Determining the Safety Integrity Level (SIL)
The achievable Safety Integrity Level is determined by the following safety-related parameters:
-
Average probability of dangerous failures of a safety function on demand (PFD
avg
),
-
Hardware Fault Tolerance (HFT) and
-
Safe Failure Fraction (SFF).
The specific safety-related parameters for the 701150 measuring system may be found in the table of the "Safety-related pa-
rameters" chapter.
The following table shows how the "Safety Integrity Level" (SIL) depends on the "average probability of dangerous failures of a
safety function of the entire safety-related system" (PFD
avg
) according to DIN EN 61 508. The "low demand mode" is consid-
ered, i. e. the demand rate for the safety-related system averages once a year.
Table High Demand PFH
Safety Integrity Level
(SIL)
Operating mode with high demand rate
PFH (high demand mode)
4
≥
10
-9
to <10
-8
3
≥
10
-8
to <10
-7
2
≥
10
-7
to <10
-6
1
≥
10
-6
to <10
-5