JUMO 14597 safetyM STB/STW Ex - Safety Temperature Limiter and Safety Temperature Monitor Operating Manual - Manual (Page 48)

6 Safety Manual
2013-04-01 42
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 measuring system of the JUMO safetyM STB/STW Ex can be found in the table
in the "Safety-related parameters" 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 61508. The "low demand mode" is consid-
ered, i.e. the demand rate for the safety-related system averages once a year.
Table: High demand table PFH
Table 6: High demand table 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