From c4b274f70fb3c4f003bf5686ecab3b5492500e27 Mon Sep 17 00:00:00 2001 From: Robin Clark Date: Tue, 8 Nov 2011 20:28:24 +0000 Subject: [PATCH] Jane Davies proof read/comments --- presentations/fmea/fmea_pres.tex | 142 ++++++++++++++++++++----------- 1 file changed, 90 insertions(+), 52 deletions(-) diff --git a/presentations/fmea/fmea_pres.tex b/presentations/fmea/fmea_pres.tex index a562a15..516fbdc 100644 --- a/presentations/fmea/fmea_pres.tex +++ b/presentations/fmea/fmea_pres.tex @@ -111,11 +111,11 @@ For the sake of example let us choose resistor R1 in the OP-AMP gain circuitry. \begin{frame} Note here that we have had to look at the failure~mode -in relation to the entire circuit. +in relation to the entire circuit. \pause We have used intuition to determine the probable -effect of this failure mode. +effect of this failure mode. \pause We have not examined this failure mode -against every other component in the system. +against every other component in the system. \pause Perhaps we should.... this would be a more rigorous and complete approach in looking for system failures. @@ -162,14 +162,14 @@ $100*99*3=29,700$. \frametitle{Rigorous Double Failure FMEA} For looking at potential double failure scenarios (two components failing within a given time frame) and the order becomes -$N^3$. +$N^3$. \pause \begin{equation} \label{eqn:fmea_double} N.(N-1).(N-2).f % \\ %(N^2 - N).f \end{equation} - + \pause $100*99*98*3=2,910,600$. \pause @@ -198,14 +198,14 @@ double failure scenarios (for burner lock-out scenarios). \begin{frame} \frametitle{PFMEA} Production FMEA (or PFMEA), is FMEA used to prioritise, in terms of -cost, problems to be addressed in product production. +cost, problems to be addressed in product production.\pause It focuses on known problems, determines the -frequency they occur and their cost to fix. +frequency they occur and their cost to fix.\pause This is multiplied together and called an RPN -number. +number.\pause Fixing problems with the highest RPN number -will return most cost benefit. +will return most cost benefit.\pause \end{frame} @@ -326,8 +326,8 @@ Applies some Bayesian statistics (probabilities of component failures and those \begin{frame} \frametitle{ FMECA - Failure Modes Effects and Criticality Analysis} Very similar to PFMEA, but instead of cost, a criticality or -seriousness factor is ascribed to putative top level incidents. -FMECA has three probability factors for component failures. +seriousness factor is ascribed to putative top level incidents.\pause +FMECA has three probability factors for component failures.\pause \textbf{FMECA ${\lambda}_{p}$ value.} This is the overall failure rate of a base component. @@ -347,11 +347,11 @@ a particular failure~mode occurring within a component. \pause reference FMD-91. \frametitle{ FMECA - Failure Modes Effects and Criticality Analysis} \textbf{FMECA $\beta$ value.} The second probability factor $\beta$, is the probability that the failure mode -will cause a given system failure. +will cause a given system failure.\pause This corresponds to `Bayesian' probability, given a particular component failure mode, the probability of a given system level failure. \pause -\textbf{FMECA `t' Value} +\textbf{FMECA `t' Value}\pause The time that a system will be operating for, or the working life time of the product is represented by the variable $t$. %for probability of failure on demand studies, @@ -360,7 +360,7 @@ represented by the variable $t$. \textbf{Severity `s' value} A weighting factor to indicate the seriousness of the putative system level error. %Typical classifications are as follows:~\cite{fmd91} - +\pause \begin{equation} C_m = {\beta} . {\alpha} . {{\lambda}_p} . {t} . {s} \end{equation} @@ -386,34 +386,59 @@ for a project manager. \end{frame} + + + + \begin{frame} + \frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} -FMEDA is the methodology behind statistical (safety integrity level) -type standards (EN61508/IOC5108). \pause -It provides a statistical overall level of safety -and allows diagnostic mitigation for self checking etc. \pause -It provides guidelines for the design and architecture -of computer/software systems for the four levels of -safety Integrity. -%For Hardware -\pause -FMEDA does force the user to consider all components in a system -by requiring that a MTTF value is assigned for each failure~mode; \pause -the MTTF may be statistically mitigated (improved) -if it can be shown that self-checking will detect failure modes. + +\begin{itemize} + \pause \item \textbf{Statistical Safety} \pause Safety Integrity Level (SIL) standards (EN61508/IOC5108). + \pause \item \textbf{Diagnostics} \pause Diagnostic or self checking elements modelled + \pause \item \textbf{Complete Failure Mode Coverage} \pause All failure modes of all components must be in the model + \pause \item \textbf{Guidelines} \pause To system architectures and development processes +\end{itemize} + +% FMEDA is the methodology behind statistical (safety integrity level) +% type standards (EN61508/IOC5108). \pause +% It provides a statistical overall level of safety +% and allows diagnostic mitigation for self checking etc. \pause +% It provides guidelines for the design and architecture +% of computer/software systems for the four levels of +% safety Integrity. +% %For Hardware +% \pause +% FMEDA does force the user to consider all components in a system +% by requiring that a MTTF value is assigned for each failure~mode; \pause +% the MTTF may be statistically mitigated (improved) +% if it can be shown that self-checking will detect failure modes. + \end{frame} + + + + \begin{frame} \frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} -Failure modes are classified as Safe or Dangerous according -to the putative system level failure they will cause. \pause -The Failure modes are also classified as Detected or -Undetected. -This gives us four level failure mode classifications: -Safe-Detected (SD), Safe-Undetected (SU), Dangerous-Detected (DD) or Dangerous-Undetected (DU), -and the probabilistic failure rate of each classification -is represented by lambda variables -(i.e. $\lambda_{SD}$, $\lambda_{SU}$, $\lambda_{DD}$, $\lambda_{DU}$). + \begin{itemize} + \pause \item \textbf{Safe or Dangerous} \pause Failure modes are classified SAFE or DANGEROUS + \pause \item \textbf{Detectable failure modes} \pause Failure modes are given the attribute DETECTABLE or UNDETECTABLE + \pause \item \textbf{Four attributes to Failure Modes} \pause All failure modes may thus be Safe Detected(SD), Safe Undetected(SU), Dangerous Detected(DD), Dangerous Undetected(DU) + \pause \item \textbf{Four statistical properties of a system} \pause $\lambda_{SD}$, $\lambda_{SU}$, $\lambda_{DD}$, $\lambda_{DU}$ +\end{itemize} + +% Failure modes are classified as Safe or Dangerous according +% to the putative system level failure they will cause. \pause +% The Failure modes are also classified as Detected or +% Undetected. +% This gives us four level failure mode classifications: +% Safe-Detected (SD), Safe-Undetected (SU), Dangerous-Detected (DD) or Dangerous-Undetected (DU), +% and the probabilistic failure rate of each classification +% is represented by lambda variables +% (i.e. $\lambda_{SD}$, $\lambda_{SU}$, $\lambda_{DD}$, $\lambda_{DU}$). \end{frame} \begin{frame} \frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} @@ -557,7 +582,7 @@ judged to be in critical sections of the product. \end{frame} -\subsection{FMEA - Better Metodology - Wish List} +\subsection{FMEA - Better Methodology - Wish List} \begin{frame} \frametitle{FMEA - Better Metodology - Wish List} @@ -596,14 +621,23 @@ judged to be in critical sections of the product. % %(N^2 - N).f % \end{equation} +\begin{itemize} + + \pause \item Analysis occurs in small stages, within {\fgs} + \pause \item Each {\fg} is analysed until we have a set of its symptoms of failure. + \pause \item A {\dc} is created with its failure modes being the symptoms from the {\fg} + \pause \item We can now use {\dcs} as higher level components + \pause \item We can build a failure model hierarchy in this way + %\pause \item +\end{itemize} -The FMMD methodology breaks the analysis down into small stages, -by making the analyst choose {\fgs} of components, to which FMEA is applied. -When analysed, a set of symptoms of failure for the {\fg} is used to create a derived~component. \pause -The derived components failure modes, are the symptoms of the {\fg} -from which it was derived. \pause -We can use derived components to form `higher~level' {\fgs}. -This creates an analysis hierarchy. +% The FMMD methodology breaks the analysis down into small stages, +% by making the analyst choose {\fgs} of components, to which FMEA is applied. +% When analysed, a set of symptoms of failure for the {\fg} is used to create a derived~component. \pause +% The derived components failure modes, are the symptoms of the {\fg} +% from which it was derived. \pause +% We can use derived components to form `higher~level' {\fgs}. +% This creates an analysis hierarchy. \end{frame} @@ -617,8 +651,8 @@ This creates an analysis hierarchy. \pause \item Collect Symptoms. \pause \item Create a '{\dc}', where its failure modes are the symptoms of the {\fg} from which it was derived. \pause \item The {\dc} is now available to be used in higher level {\fgs}. - \pause \item We can represent this process as a function which converts a {\fg} into a {\dc} and use the symbol $ \bowtie $ to represet it. - \pause i.e. $ \bowtie ( FunctionalGroup ) \rightarrow {DerivedComponent} $ + %\pause \item We can represent this process as a function which converts a {\fg} into a {\dc} and use the symbol $ \bowtie $ to represet it. + \pause $ \bowtie ( FunctionalGroup ) \rightarrow {DerivedComponent} $ %\item could use AMALG instead here $ \amalg $ \end{itemize} \end{frame} @@ -634,7 +668,7 @@ This creates an analysis hierarchy. % mvampcircuit.png: 243x143 pixel, 72dpi, 8.57x5.04 cm, bb=0 0 243 143 \end{figure} -We can return to the milli-volt amplifier as an example to analyse. +We return to the milli-volt amplifier as an example to analyse. \pause We can begin by looking for functional groups.\pause The resistors perform a fairly common function in electronics, that of the potential divider. @@ -786,10 +820,11 @@ in a higher level design. \begin{frame} \frametitle{FMMD - Failure Mode Modular De-Composition} -We can view the functional groups in FMMD as forming a hierarchy. -If for the sake of example we consider each functional group to -be three components, the figure below shows -how the levels work and converge to a top or system level. +%We can view the functional groups in FMMD as forming a hierarchy. +%If +% For the sake of example we consider each functional group to +% be three components, the figure below shows +% how the levels work and converge to a top or system level. \begin{figure} \centering \includegraphics[width=300pt]{./three_tree.png} @@ -797,7 +832,10 @@ how the levels work and converge to a top or system level. \caption{Functional Group Tree example} \label{fig:three_tree} \end{figure} - +\pause +For the sake of example we consider each functional group to +be three components, the figure below shows +how the levels work and converge to a top or system level. \end{frame} \begin{frame}