From 94b40f096e0884589cd5d84420a91f21d8ca384c Mon Sep 17 00:00:00 2001 From: Robin Clark Date: Tue, 10 May 2011 18:41:33 +0100 Subject: [PATCH] Added FMEA section --- noninvopamp/noninvopamp.tex | 89 ++++++++++++++++++++++++++++++++++--- 1 file changed, 82 insertions(+), 7 deletions(-) diff --git a/noninvopamp/noninvopamp.tex b/noninvopamp/noninvopamp.tex index d54554a..0bc15da 100644 --- a/noninvopamp/noninvopamp.tex +++ b/noninvopamp/noninvopamp.tex @@ -280,8 +280,8 @@ We can now derive a `component' to represent this amplifier configuration (see f %failure mode contours). %\clearpage - -\section{Failure Mode as a Directed Acyclic Graph} +\clearpage +\section{Failure Modes from non inverting amplifier as a Directed Acyclic Graph (DAG)} We can now represent the FMMD analysis as a directed graph, see figure \ref{fig:noninvdag0}. With the information structured in this way, we can trace the high level failure mode symptoms @@ -411,7 +411,7 @@ back to their potential causes. -%\clearpage + \section{Extracting Fault Trees from the DAG} @@ -525,13 +525,88 @@ The FTA diagram directly derived from the FMMD DAG is shown in figure \ref{fig:n %\clearpage -show an example fault tree, showing the causes and logical (only OR's here) +%show an example fault tree, showing the causes and logical (only OR's here) -\section{Extracting FMEA Analysis from the DAG} +\subsection{Information missing in FTA} -Extract for each component failure mode the system level cause +to expand: Each FTA deals only with one symptom. + +\subsubsection{Further refinements} + +to expand: Cuts sets and minimal cut sets. + + +\clearpage +\section{Assisting FMEA reports from the DAG} + +A design FMEA, or potential failure mode and effects analysis +will typically require the designer to look at the possible effects +of all the component failure modes in the system under investigation. +\ifthenelse {\boolean{paper}} +{ +%FMEA - brief description for paper... +Design FMEA is methodology for assessing potential reliability/dangerous condition early +in the development cycle. +FMEA is used to identify potential failure modes, +determine their effect on the operation of the product, +and identify actions to mitigate the failures. +FMEA relies anticipating what {\em might} go wrong with a product. +While anticipating every failure mode is not possible, a development team should +collate as complete a list of potential failure modes as possible. +With an FMMD sourced failure mode to symptom mapping, this +list should be more complete. It will for instance include +not only an entry every component failure mode, but has a formal +reasoning process behind it, which leads to the symptom. +} +{ +See section \ref{pfmea} for an overview of FMEA. +FMEA relies anticipating what {\em might} go wrong with a product. +While anticipating every failure mode is not possible, a development team should +collate as complete a list of potential failure modes as possible. +With an FMMD sourced failure mode to symptom mapping, this +list should be more complete. It will for instance include +not only an entry every component failure mode, but has a formal +reasoning process behind it, which leads to the symptom. +} +We have from the DAG model, a direct path from each component failure +mode to potential symptoms. This allows us to partially fill in +the FMEA report. The detectability and severity of the symptom +are subjective. Given component failure rates, the probability +of the the potential cause occurring can be calculated, using the FMD-91~\cite{fmd91} and MIL1991~\cite{mil1991} +component failure mode statistical references. + +\begin{table}[ht] +\caption{Non Inverting Amplifier: Failure Mode Effects Analysis: Single Faults} % title of Table +\centering % used for centering table +\begin{tabular}{||l|l|c|l|c|c|c||} +\hline \hline + \textbf{Item} & \textbf{Potential Failure} & \textbf{ Sev } & \textbf{Potential} & \textbf{prob} & \textbf{det} & \textbf{RPN} \\ + \textbf{Function} & \textbf{mode} & \textbf{ /cost }& \textbf{Cause} & \textbf{/occ } & \textbf{} & \\\hline +\hline + Non Inverting & $AMP_{high}$ & & $R1_{short} $ & & & \\ + Amplifier & $AMP_{low}$ & & $R1_{open} $ & & & \\ + Circuit & $AMP_{low}$ & & $R2_{short} $ & & & \\ + & $AMP_{high}$ & & $R2_{open}$ & & & \\ + + & $AMP_{lowpass}$ & & $OPAMP_{lowslew}$ & & & \\ + & $AMP_{low}$ & & $OPAMP_{latchdown}$ & & & \\ + & $AMP_{high}$ & & $OPAMP_{latchup}$ & & & \\ + & $AMP_{low}$ & & $OPAMP_{noop} $ & & & \\ + + +\hline +\hline +\hline +\end{tabular} +\label{ampfmea} +\end{table} + +\subsection{Information missing in FMEA} + +to expand: Each FMEA looses the reasoning in the FMMD Hierarchy/DAG for linking +the symptoms to the potential causes. +FMEA can miss symptoms especially where a component failure mode may cause more than one top-level symptom. -\section{Extracting FMECA from the DAG} Work out the alpha and beta values !!!