6 safety manual – JUMO 14597 safetyM STB/STW Ex - Safety Temperature Limiter and Safety Temperature Monitor Operating Manual User Manual
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6 Safety Manual
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6.8.2
Failure rates and SFF for type 701155/X-XX-025X-XXXX-25 (AC/DC 24 V)
Important information:
Variants 1 to 4 were evaluated with JUMO probes according to data sheets 901006 and 902006.
For variant 5 no sensor system was included (only the JUMO safety
M STB/STW Ex).
In this case, the plant operator selects the sensor system.
The PFH and PFD
avg
values were calculated with the assumption that the time to restore the system is 8 h (MTTR = 72 h). Fur-
thermore, the calculation was based on a lifetime of 10 years (T
1
= 10 y). The Common Cause Factor was determined accord-
ing to the tables of DIN EN 61508 for sensor systems and logic.
Table 5:
Variant
λ
s
[Fit]
λ
dd
[Fit]
λ
du
[Fit]
SFF
PFH (1/h)
PFD
avg
1
919.23
306.82
34.24
96 %
7.22 e
-9
3.19 e
-4
1a
919.23
306.82
34.24
96 %
3.71 e
-9
1.63 e
-4
2
886.19
303.86
34.24
96 %
3.71 e
-9
1.63 e
-4
3
947.18
325.86
37.89
96 %
3.75 e
-9
1.64 e
-4
4
953.24
350.21
40.59
96 %
3.85 e
-9
1.69 e
-4
5
938.89
323.57
36.89
96 %
3.68 e
-9
1.61 e
-4