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presentations/fmea/fmea_pres.tex
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@ -111,11 +111,11 @@ For the sake of example let us choose resistor R1 in the OP-AMP gain circuitry.
\begin{frame} \begin{frame}
Note here that we have had to look at the failure~mode 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 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 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 Perhaps we should.... this would be a more rigorous and complete
approach in looking for system failures. approach in looking for system failures.
@ -162,14 +162,14 @@ $100*99*3=29,700$.
\frametitle{Rigorous Double Failure FMEA} \frametitle{Rigorous Double Failure FMEA}
For looking at potential double failure scenarios (two components For looking at potential double failure scenarios (two components
failing within a given time frame) and the order becomes failing within a given time frame) and the order becomes
$N^3$. $N^3$. \pause
\begin{equation} \begin{equation}
\label{eqn:fmea_double} \label{eqn:fmea_double}
N.(N-1).(N-2).f % \\ N.(N-1).(N-2).f % \\
%(N^2 - N).f %(N^2 - N).f
\end{equation} \end{equation}
\pause
$100*99*98*3=2,910,600$. $100*99*98*3=2,910,600$.
\pause \pause
@ -198,14 +198,14 @@ double failure scenarios (for burner lock-out scenarios).
\begin{frame} \begin{frame}
\frametitle{PFMEA} \frametitle{PFMEA}
Production FMEA (or PFMEA), is FMEA used to prioritise, in terms of 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 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 This is multiplied together and called an RPN
number. number.\pause
Fixing problems with the highest RPN number Fixing problems with the highest RPN number
will return most cost benefit. will return most cost benefit.\pause
\end{frame} \end{frame}
@ -326,8 +326,8 @@ Applies some Bayesian statistics (probabilities of component failures and those
\begin{frame} \begin{frame}
\frametitle{ FMECA - Failure Modes Effects and Criticality Analysis} \frametitle{ FMECA - Failure Modes Effects and Criticality Analysis}
Very similar to PFMEA, but instead of cost, a criticality or Very similar to PFMEA, but instead of cost, a criticality or
seriousness factor is ascribed to putative top level incidents. seriousness factor is ascribed to putative top level incidents.\pause
FMECA has three probability factors for component failures. FMECA has three probability factors for component failures.\pause
\textbf{FMECA ${\lambda}_{p}$ value.} \textbf{FMECA ${\lambda}_{p}$ value.}
This is the overall failure rate of a base component. 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} \frametitle{ FMECA - Failure Modes Effects and Criticality Analysis}
\textbf{FMECA $\beta$ value.} \textbf{FMECA $\beta$ value.}
The second probability factor $\beta$, is the probability that the failure mode 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 This corresponds to `Bayesian' probability, given a particular
component failure mode, the probability of a given system level failure. component failure mode, the probability of a given system level failure.
\pause \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 The time that a system will be operating for, or the working life time of the product is
represented by the variable $t$. represented by the variable $t$.
%for probability of failure on demand studies, %for probability of failure on demand studies,
@ -360,7 +360,7 @@ represented by the variable $t$.
\textbf{Severity `s' value} \textbf{Severity `s' value}
A weighting factor to indicate the seriousness of the putative system level error. A weighting factor to indicate the seriousness of the putative system level error.
%Typical classifications are as follows:~\cite{fmd91} %Typical classifications are as follows:~\cite{fmd91}
\pause
\begin{equation} \begin{equation}
C_m = {\beta} . {\alpha} . {{\lambda}_p} . {t} . {s} C_m = {\beta} . {\alpha} . {{\lambda}_p} . {t} . {s}
\end{equation} \end{equation}
@ -386,34 +386,59 @@ for a project manager.
\end{frame} \end{frame}
\begin{frame} \begin{frame}
\frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} \frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis}
FMEDA is the methodology behind statistical (safety integrity level)
type standards (EN61508/IOC5108). \pause \begin{itemize}
It provides a statistical overall level of safety \pause \item \textbf{Statistical Safety} \pause Safety Integrity Level (SIL) standards (EN61508/IOC5108).
and allows diagnostic mitigation for self checking etc. \pause \pause \item \textbf{Diagnostics} \pause Diagnostic or self checking elements modelled
It provides guidelines for the design and architecture \pause \item \textbf{Complete Failure Mode Coverage} \pause All failure modes of all components must be in the model
of computer/software systems for the four levels of \pause \item \textbf{Guidelines} \pause To system architectures and development processes
safety Integrity. \end{itemize}
%For Hardware
\pause % FMEDA is the methodology behind statistical (safety integrity level)
FMEDA does force the user to consider all components in a system % type standards (EN61508/IOC5108). \pause
by requiring that a MTTF value is assigned for each failure~mode; \pause % It provides a statistical overall level of safety
the MTTF may be statistically mitigated (improved) % and allows diagnostic mitigation for self checking etc. \pause
if it can be shown that self-checking will detect failure modes. % 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} \end{frame}
\begin{frame} \begin{frame}
\frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} \frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis}
Failure modes are classified as Safe or Dangerous according \begin{itemize}
to the putative system level failure they will cause. \pause \pause \item \textbf{Safe or Dangerous} \pause Failure modes are classified SAFE or DANGEROUS
The Failure modes are also classified as Detected or \pause \item \textbf{Detectable failure modes} \pause Failure modes are given the attribute DETECTABLE or UNDETECTABLE
Undetected. \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)
This gives us four level failure mode classifications: \pause \item \textbf{Four statistical properties of a system} \pause $\lambda_{SD}$, $\lambda_{SU}$, $\lambda_{DD}$, $\lambda_{DU}$
Safe-Detected (SD), Safe-Undetected (SU), Dangerous-Detected (DD) or Dangerous-Undetected (DU), \end{itemize}
and the probabilistic failure rate of each classification
is represented by lambda variables % Failure modes are classified as Safe or Dangerous according
(i.e. $\lambda_{SD}$, $\lambda_{SU}$, $\lambda_{DD}$, $\lambda_{DU}$). % 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} \end{frame}
\begin{frame} \begin{frame}
\frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} \frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis}
@ -557,7 +582,7 @@ judged to be in critical sections of the product.
\end{frame} \end{frame}
\subsection{FMEA - Better Metodology - Wish List} \subsection{FMEA - Better Methodology - Wish List}
\begin{frame} \begin{frame}
\frametitle{FMEA - Better Metodology - Wish List} \frametitle{FMEA - Better Metodology - Wish List}
@ -596,14 +621,23 @@ judged to be in critical sections of the product.
% %(N^2 - N).f % %(N^2 - N).f
% \end{equation} % \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, % The FMMD methodology breaks the analysis down into small stages,
by making the analyst choose {\fgs} of components, to which FMEA is applied. % 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 % 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} % The derived components failure modes, are the symptoms of the {\fg}
from which it was derived. \pause % from which it was derived. \pause
We can use derived components to form `higher~level' {\fgs}. % We can use derived components to form `higher~level' {\fgs}.
This creates an analysis hierarchy. % This creates an analysis hierarchy.
\end{frame} \end{frame}
@ -617,8 +651,8 @@ This creates an analysis hierarchy.
\pause \item Collect Symptoms. \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 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 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 \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 $ \bowtie ( FunctionalGroup ) \rightarrow {DerivedComponent} $
%\item could use AMALG instead here $ \amalg $ %\item could use AMALG instead here $ \amalg $
\end{itemize} \end{itemize}
\end{frame} \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 % mvampcircuit.png: 243x143 pixel, 72dpi, 8.57x5.04 cm, bb=0 0 243 143
\end{figure} \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 \pause
We can begin by looking for functional groups.\pause We can begin by looking for functional groups.\pause
The resistors perform a fairly common function in electronics, that of the potential divider. 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} \begin{frame}
\frametitle{FMMD - Failure Mode Modular De-Composition} \frametitle{FMMD - Failure Mode Modular De-Composition}
We can view the functional groups in FMMD as forming a hierarchy. %We can view the functional groups in FMMD as forming a hierarchy.
If for the sake of example we consider each functional group to %If
be three components, the figure below shows % For the sake of example we consider each functional group to
how the levels work and converge to a top or system level. % be three components, the figure below shows
% how the levels work and converge to a top or system level.
\begin{figure} \begin{figure}
\centering \centering
\includegraphics[width=300pt]{./three_tree.png} \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} \caption{Functional Group Tree example}
\label{fig:three_tree} \label{fig:three_tree}
\end{figure} \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} \end{frame}
\begin{frame} \begin{frame}