Results Of The Assessment - turck IM1-12-R Handbuch

Sicherheitshandbuch – Trennschaltverstärker

5 Results of the assessment

exida.com did the FMEDAs together with Werner Turck GmbH & Co. KG.
For the calculation of the Safe Failure Fraction (SFF) the following has to be noted:
λ
consists of the sum of all component failure rates. This means:
total
λ = λ + λ
total safe dangerous
SFF = 1 – λ / λ
du
For the FMEDAs failure modes and distributions were used based on information gained from
[N3] to [N5].
For the calculation of the PFD
after a complete proof test all states are going back to the OK state no proof test rate is shown
in the Markov models but included in the calculation.
The proof test time was changed using the Microsoft® Excel 2000 based FMEDA tool of
exida.com as a simulation tool. The results are documented in the following sections.
λ
d
d
Figure 3: Markov model for a 1oo1 structure
© exida.com GmbH
Stephan Aschenbrenner
30
+ λ
.
no effect
total
the following Markov model for 1oo1 system was used. As
AVG
ok
τ
Repair
λ
s
s
Abbreviations:
d The system has failed dangerous
s The system has failed safe
λ
Failure rate of dangerous failures
d
λ
Failure rate of safe failures
s
T Repair time
Repair
τ
Repair rate (1 / T
Repair
TURCK 04-07-14 R002 V3R0.doc; February 21, 2014
Hans Turck GmbH & Co. KG • Tel. +49 208/4952-0 • Fax +49 208/4952-264
)
Repair
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