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thats fucking it. Enough for today

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Robin Clark 2013-08-10 21:29:38 +01:00
parent 8f4861bfdf
commit 296ad42e60
2 changed files with 9 additions and 8 deletions
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11
submission_thesis/CH2_FMEA/copy.tex
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@ -1195,8 +1195,7 @@ and require re-design of some systems.
%
\begin{table}[ht]
\centering
\caption{Table adapted from EN61508-1:2001 [7.6.2.9 p33], showing statistical tolerance of `dangerous~failures' to
comply with a given SIL level} % title of Table
%\centering % used for centering table
\begin{tabular}{|| l | l | c | c | l ||} \hline
\textbf{SIL} & \textbf{Low Demand} & \textbf{Continuous Demand} \\
@ -1208,6 +1207,8 @@ comply with a given SIL level} % title of Table
\hline
\end{tabular}
\caption{Table adapted from EN61508-1:2001 [7.6.2.9 p33], showing statistical tolerance of `dangerous~failures' to
comply with a given SIL level} % title of Table
\label{tbl:sil_levels}
\end{table}
%
@ -1225,7 +1226,7 @@ self checking features on safety, and provides detailed recommendations for comp
FMEDA is the fundamental methodology of the statistical (safety integrity level)
type standards (EN61508/IOC5108).
The end result of an EN61508 analysis is an % provides a statistical
overall `level~of~safety' known as a Safety Integrity level (SIL), for an installed system.
overall `level~of~safety' known as a Safety Integrity level (SIL) assigned to an installed system.
%
It has a simple final result, a Safety Integrity Level (SIL) from 1 to 4 (where 4 is safest).
%
@ -1233,8 +1234,8 @@ These SIL levels are broadly linked to the concept of an
acceptance of given probabilities of dangerous
failures against time, as shown in table~\ref{tbl:sil_levels}.
%
The philosophy behind this is that is recognised that no system can have a perfect
safety integrity, but risk and criticality can be matched to acceptable,
The philosophy behind this is that it is recognised that no system can have a perfect
safety integrity, but that risk and criticality can be matched to acceptable,
or realistic levels of risk.
%There are currently four SIL `levels', one to four, with four being the highest level.
%

6
submission_thesis/CH3_FMEA_criticism/copy.tex
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@ -32,7 +32,7 @@ now software/hardware hybrids.
%
Even analogue electronics, with the advent of surface mount and miniature components,
means that a modern electronic circuits are typically far more complex and have
means that modern electronic circuits are typically far more complex and have
far higher component counts, than those
of the era when FMEA methodologies were invented.
%
@ -62,9 +62,9 @@ for an improved methodology.
\subsection{FMEA: {\bc} {\fm} to system level failure modelling}
FMEA traces it roots to the 1940s when it was used to identify the most costly
failures arising from car mass-production~\cite{bfmea}.
It was later modified slightly to include severity of the top level failure (FMECA~\cite{fmeca}).
It was later modified slightly to identify/compare severity levels of the system level failures (FMECA~\cite{fmeca}).
In the 1980s FMEA was extended again (FMEDA~\cite{fmeda}) to provide statistics
for predicting failure rates.
for predicting safety~levels/failure~rates.
%
However a typical entry in each of the above methodologies, starts with a
particular component failure mode and associates it with a system---or top level---failure symptom.