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now have 1,2,3 8
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Robin P. Clark 2013-09-11 16:33:22 +01:00
parent a476926969
commit d7dee62f42
1 changed files with 8 additions and 6 deletions
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submission_thesis/CH8_Conclusion/copy.tex
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@ -258,8 +258,8 @@ resistor{\lambda}_p = {\lambda}_{b}{\pi}_Q{\pi}_E
Thus thermistor, bead type, `non~military~spec' is given a FIT of 315.0. Thus thermistor, bead type, `non~military~spec' is given a FIT of 315.0.
% %
\frategloss \frategloss
Using the RIAC finding the following table (table \ref{tab:stat_single}) can be created, Using the RIAC finding the following (table~\ref{tab:stat_single}) can be created which
showing the FIT values for all single failure modes. presents the FIT values for all single failure modes.
%\glossary{name={FIT}, description={Failure in Time (FIT). The number of times a particular failure is expected to occur in a $10^{9}$ hour time period.}} %\glossary{name={FIT}, description={Failure in Time (FIT). The number of times a particular failure is expected to occur in a $10^{9}$ hour time period.}}
\fmmdglossFIT \fmmdglossFIT
% %
@ -331,7 +331,7 @@ failure rate statistics to double failures can also be determined.
%% %%
% %
Considering the failure modes to be statistically independent Considering the failure modes to be statistically independent
the FIT values for all the combinations the FIT values for all the combinations of
failures in the electronic examples from chapter~\ref{sec:chap5} in table~\ref{tab:ptfmea2} can be calculated. failures in the electronic examples from chapter~\ref{sec:chap5} in table~\ref{tab:ptfmea2} can be calculated.
% %
The failure mode of most concern, the undetectable {\textbf{FLOATING}} condition, The failure mode of most concern, the undetectable {\textbf{FLOATING}} condition,
@ -339,8 +339,9 @@ requires that resistors $R_1$ and $R_2$ both fail.
% %
Multiplying the MTTF probabilities for these types of resistor failing gives the MTTF for both failing. Multiplying the MTTF probabilities for these types of resistor failing gives the MTTF for both failing.
% %
The FIT value of 12.42 corresponds to The FIT value of 12.42 corresponds to $12.42 \times {10}^{-9}$ failures per hour.
$12.42 \times {10}^{-9}$ failures per hour. Squaring this gives $ 154.3 \times {10}^{-18} $. %
Squaring this gives $ 154.3 \times {10}^{-18} $.
% %
This is an astronomically small MTTF, and so small that it would This is an astronomically small MTTF, and so small that it would
probably fall below a threshold to sensibly consider. probably fall below a threshold to sensibly consider.
@ -359,7 +360,8 @@ In a large FMMD model, system/top level failures can be traced
down to {\bc} {\fms}. down to {\bc} {\fms}.
% %
To determine the MTTF probability To determine the MTTF probability
for a system level failure, the MTTF statistics are added for all its possible causes. for a system level failure,
the MTTF statistics are added for all its possible causes.
% %
Thus even for large FMMD models accurate Thus even for large FMMD models accurate
statistics for electronic sourced failures can be calculated. statistics for electronic sourced failures can be calculated.