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Robin Clark 2011-09-30 13:53:38 +01:00
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presentations/fmea/fmea_pres.tex
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@ -352,14 +352,53 @@ against all safe and dangerous failure probabilities.
Again this is usually expressed as a percentage. Again this is usually expressed as a percentage.
$$ SFF = \big( \Sigma\lambda_S + \Sigma\lambda_{DD} \big) / \big( \Sigma\lambda_S + \Sigma\lambda_D \big) $$ $$ SFF = \big( \Sigma\lambda_S + \Sigma\lambda_{DD} \big) / \big( \Sigma\lambda_S + \Sigma\lambda_D \big) $$
SFF determines how proportionately fail-safe a system is, not how reliable it is !
\end{frame} \end{frame}
\begin{frame} \begin{frame}
\frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} \frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis}
SIL Levels are how they are calculated To achieve SIL levels, diagnostic coverage and SFF levels are prescribed along with
hardware architectures and software techniques.
Over all the aim of SIL is classify the safety of a system,
by statistically determining how frequently it can fail dangerously.
\end{frame} \end{frame}
\begin{frame}
\frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis}
{
\begin{table}[ht]
\caption{FMEA Calculations} % title of Table
%\centering % used for centering table
\begin{tabular}{|| l | l | c | c | l ||} \hline
\textbf{SIL} & \textbf{Low Demand} & \textbf{Continuous Demand} \\
& Prob of failing on demand & Prob of failure per hour \\ \hline \hline
4 & $ 10^{-5}$ to $< 10^{-4}$ & $ 10^{-9}$ to $< 10^{-8}$ \\ \hline
3 & $ 10^{-4}$ to $< 10^{-3}$ & $ 10^{-8}$ to $< 10^{-7}$ \\ \hline
2 & $ 10^{-3}$ to $< 10^{-2}$ & $ 10^{-7}$ to $< 10^{-6}$ \\ \hline
1 & $ 10^{-2}$ to $< 10^{-1}$ & $ 10^{-6}$ to $< 10^{-5}$ \\ \hline
\hline
\end{tabular}
\end{table}
}
Table adapted from EN61508-1:2001 [7.6.2.9 p33]
\end{frame}
\begin{frame}
\frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis}
FMEDA is a modern extension of FMEA, in that it will allow for
self checking features, and provides detailed recommendations for computer/software architecture.
It also has a simple final result, a Safety Integrity Level (SIL) from 1 to 4 (where 4 is safest).
FMEA can be used as a term simple to mean Failure Mode Effects Analysis, and is
part of product approval for many regulated products in the EU and the USA...
\end{frame}
\section{FMEA used for Safety Critical Approvals} \section{FMEA used for Safety Critical Approvals}
@ -410,9 +449,7 @@ judged to be in critical sections of the product.
\pause \item FMEA type methodologies were designed for simple electro-mechanical systems of the 1940's to 1960's. \pause \item FMEA type methodologies were designed for simple electro-mechanical systems of the 1940's to 1960's.
\end{itemize} \end{itemize}
%FMEDA is a modern extension of FMEA, in that it will allow for %
%self checking features, and provides detailed recommendations for computer/software architecture,
%but
\end{frame} \end{frame}