7
Failure Rates in Accordance to IEC 61508
The following table summarizes the failure rates of the modules, which were calculated from Failure Mode and
Diagnostic Effects in accordance to standard IEC 61508. The information can be used in calculating probability
of dangerous failures using Reliability Block Modeling or Markov Modeling. Such modeling should consider
redundant node processors in a 1oo2, 2oo3 or 3oo4 configuration.
Model
3200T
3201
Safety Integrity Level
2
2
Safe Failure Fraction:
99.86%
99.86%
Diagnostic Coverage:
99.82%
99.83%
Failure Rates In Common Circuitry:
Safe Detected
4.1013-07
4.1013-07
Safe Undetected
8.9104E-09
8.9104E-09
Dangerous Detected
1.3305E-06
1.3305E-06
Dangerous Undetected
2.6214E-09
2.6214E-09
Don't Care
1.1026E-06
1.1026E-06
Failure Rates In Per Channel Circuitry:
Safe Detected
9.3060E-09
9.3060E-09
Safe Undetected
9.4000E-11
9.4000E-11
Dangerous Detected
2.5477E-07
2.5477E-07
Dangerous Undetected
2.3440E-10
2.3440E-10
Don't Care
6.3200E-08
6.3200E-08
Average Frequency of a Dangerous Failure per Hour
(1oo1D):
2.8558E-09
3.0902E-09
Average Frequency of a Dangerous Failure per Hour
(1oo2D):
3.5037E-10
4.0446E-10
Average Frequency of a Dangerous Failure per Hour
(2oo3D):
3.8586E-11
4.3134E-11
Mean Time to Restoration for 1oo2D (SIL-3)
configurations:
≤ 9 days
≤ 9 days
Mean Time to Restoration for all other configurations:
No restriction
No restriction
In dual redundant configurations, the users must exchange the card withi
n Mean Time to Restore (MTTR ≤ 9
days) in order to remain within SIL 3 requirements. Otherwise the card will continue to operate in degraded SIL
2 mode.
