From 9faeab90da6123cff80cf825c3f3e39f0aa4e00b Mon Sep 17 00:00:00 2001 From: Your Name Date: Mon, 12 Mar 2012 20:08:02 +0000 Subject: [PATCH] OK think I got more of the componen failure mode stuff done... --- thesis_submission/CH5_Examples/copy.tex | 142 +++++++++++++++++++----- 1 file changed, 114 insertions(+), 28 deletions(-) diff --git a/thesis_submission/CH5_Examples/copy.tex b/thesis_submission/CH5_Examples/copy.tex index 775b6b4..c602702 100644 --- a/thesis_submission/CH5_Examples/copy.tex +++ b/thesis_submission/CH5_Examples/copy.tex @@ -12,6 +12,8 @@ \usepackage{lastpage} \newcommand{\fg}{\em functional~group} +\newcommand{\fm}{\em failure mode} +\newcommand{\fms}{\em failure modes} \newcommand{\fgs}{\em functional~groups} \newcommand{\dc}{\em derived~component} \newcommand{\dcs}{\em derived~components} @@ -93,6 +95,7 @@ allowing re-use of modules and reducing the number of by-hand analysis checks to \begin{itemize} \item {\bc} - is taken to mean a `part' as defined above~\cite{scse}[p.619]. We should be able to define a set of failure modes for every {\bc}. +\item {\fm} - failure mode - the ways in which a component can fail \item {\fg} - a collection of components chosen to perform a particular task \item {\em symptom} - a failure mode of a functional group caused by one or more of its component failure modes. \item {\dc} - a new component derived from an analysed {\fg} @@ -102,14 +105,53 @@ allowing re-use of modules and reducing the number of by-hand analysis checks to \subsection{A detailed look at failure symptoms of two components: the op-amp and the resistor} +In order to apply any form of Failure Mode Effects Analysis (FMEA) we need to know the ways in which the components we are using can fail. +How base components could fail internally, its not of interest to an FMEA investigation. +The FMEA investigator needs to know what failure behaviour a component may exhibit, or in other words, its +modes of failure. + +A large body of literature exists which gives guidance for for determining component {\fms}. +For this study FMD-91~\cite{fmd91} and the gas burner standard EN298~\cite{en298}. +%Some standards prescribe specific failure modes for generic component types. +In EN298 failure modes for generic component types are prescribed, or +determined by a procedure where failure scenarios of all pins OPEN and all adjacent pins shorted +are examined. +% + +FMD-91 is a reference document released into the public domain by the United States DOD +and describes {\fms} of common electronic components. +FMD-91 entries include descriptions of internal failures along with {\fms}. +FMD-91 entries need, in some cases, some interpretation to be mapped to a clear set of +component failure modes. + + +% One is from the US military document FMD-91, where internal failures +% of components are described (with stats). +% +% The other is EN298 where the failure modes for generic component types are prescribed, or +% determined by a procedure where failure scenarios of all pins OPEN and all adjacent pins shorted +% is applied. These techniques +% +% The FMD-91 entries need, in some cases, some interpretation to be mapped to +% component failure symptoms, but include failure modes that can be due to internal failures. +% The EN298 SHORT/OPEN procedure cannot determine failures due to internal causes but can be applied to any IC. +% +% Could I come in and see you Chris to quickly discuss these. +% +% I hope to have chapter 5 finished by the end of March, chapter 5 being the +% electronics examples for the FMMD methodology. + We look in detail at two common electrical components in this section and examine how two sources of information on failure modes view their failure mode behaviour. We look at the reasons why some known failure modes are omitted, or presented in specific but unintuitive ways. %We compare the US. military published failure mode specifications wi +We then compare and contrast the failure modes determined for these components +from the FMD-91 reference source and from the guidelines of the +European burner standard EN298. -- Failure modes. Prescribed failure modes EN298 - FMD91 +%- Failure modes. Prescribed failure modes EN298 - FMD91 \subsection{resistor} @@ -186,7 +228,11 @@ $$ fm(R) = \{ OPEN, SHORT \} . $$ \subsection{op-amp} - +The op-amp is a differential amplifier and is very widely used. +They are typically packaged in dual or quad configurations---meaning +that a chip will typically contain two or four amplifiers. +For the purpose of example, we look at +a typical op-amp designed for instrumentation and measurement, the dual packaged version of the LM358~\cite{lm358}. \subsubsection{FMD-91 Op-AMP Failure Modes} @@ -194,8 +240,7 @@ $$ fm(R) = \{ OPEN, SHORT \} . $$ For OP-AMP failures modes, FMD-91\cite{fmd91}{3-116] states, \begin{itemize} \item Degraded Output 50\% Low Slew rate - poor die attach - \item No Operation - overstress 31.3\% - \item Shorted $V_+$ to $V_-$, overstress, resistive short in amplifier\% + \item No Operation - overstress 31.3\% \item Shorted $V_+$ to $V_-$, overstress, resistive short in amplifier\% \item Opened $V_+$ open\% \end{itemize} @@ -213,7 +258,7 @@ a signal may be lost. We can map this failure cause to a failure symptom, and we can call it $LOW_{slew}$. \paragraph{No Operation - over stress} -Here the OP_AMP has been damaged, and the output may be held HIGH LOW, or may be effectively tri-stated +Here the OP\_AMP has been damaged, and the output may be held HIGH LOW, or may be effectively tri-stated , i.e. not able to drive circuitry in along the next stages of te signal path: we can call theis state NOOP (no Operation). We can map this failure cause to three symptoms, $LOW$, $HIGH$, $NOOP$. @@ -233,8 +278,8 @@ We can define an OP-AMP, under FMD-91 definitions to have the following failure $$fm(OP-AMP) = \{ HIGH, LOW, NOOP, LOW_{slew} \} $$ -EN298 does not specifically define OP\_AMPS failure modes; these can be determeined -by following a generic procedure for integrated circuits outlined in +EN298 does not specifically define OP\_AMPS failure modes; these can be determined +by following a procedure for `integrated~circuits' outlined in annex~A~\cite{en298}[A.1 note e]. This demands that all open connections, and shorts between adjacent pins be considered. We can examine these failure modes by taking a typical instrumentation op-amp, say the $LM358$ %\mu741$ @@ -245,7 +290,7 @@ these conditions. \centering \includegraphics[width=200pt]{./lm258pinout.jpg} % lm258pinout.jpg: 478x348 pixel, 96dpi, 12.65x9.21 cm, bb=0 0 359 261 - \caption{Pinout for an LM258 dual OP-AMP} + \caption{Pinout for an LM358 dual OP-AMP} \label{fig:lm258} \end{figure} @@ -260,32 +305,52 @@ these conditions. \begin{table}[h+] \caption{LM358: EN298 Single failure symptom extraction} \begin{tabular}{|| l | l | c | c | l ||} \hline - \textbf{Failure Scenario} & & \textbf{Pot Div Effect} & & \textbf{Symptom} \\ + \textbf{Failure Scenario} & & \textbf{Amplifier Effect} & & \textbf{Symptom(s)} \\ \hline - FS1: PIN 1 OPEN & & $LOW$ & & $PDLow$ \\ \hline - FS2: PIN 1 OPEN & & $LOW$ & & $PDLow$ \\ \hline - FS3: PIN 1 OPEN & & $LOW$ & & $PDLow$ \\ \hline - FS4: PIN 1 OPEN & & $LOW$ & & $PDLow$ \\ \hline - FS5: PIN 1 OPEN & & $LOW$ & & $PDLow$ \\ \hline - FS6: PIN 1 OPEN & & $LOW$ & & $PDLow$ \\ \hline + & & & & \\ \hline - FS7: PIN 1 OPEN & & $LOW$ & & $PDLow$ \\ \hline - FS8: PIN 1 OPEN & & $LOW$ & & $PDLow$ \\ \hline + FS1: PIN 1 OPEN & & A output open & & $NOOP_A$ \\ \hline + + FS2: PIN 2 OPEN & & A-input disconnected, & & \\ + & & infinite gain on A+input & & $LOW_A$ or $HIGH_A$ \\ \hline + + FS3: PIN 3 OPEN & & A+input disconnected, & & \\ + & & infinite gain on A-input & & $LOW_A$ or $HIGH_A$ \\ \hline + + FS4: PIN 4 OPEN & & power to chip (ground) disconnected & & $NOOP_A$ and $NOOP_B$ \\ \hline - FS2: R1 OPEN & & $HIGH$ & & $PDHigh$ \\ \hline + FS5: PIN 5 OPEN & & B+input disconnected, & & \\ + & & infinite gain on B-input & & $LOW_B$ or $HIGH_B$ \\ \hline + + FS6: PIN 6 OPEN & & B-input disconnected, & & \\ + FS6: PIN 6 OPEN & & infinite gain on B+input & & $LOW_B$ or $HIGH_B$ \\ \hline + FS7: PIN 7 OPEN & & B output open & & $NOOP_B$ \\ \hline + FS8: PIN 8 OPEN & & power to chip & & \\ + FS8: PIN 8 OPEN & & (Vcc) disconnected & & $NOOP_A$ and $NOOP_B$ \\ \hline + & & & & \\ + & & & & \\ + & & & & \\ \hline + FS9: PIN 1 $\stackrel{short}{\longrightarrow}$ PIN 2 & & A -ve 100\% Feed back, low gain & & $LOW_A$ \\ \hline - FS3: R2 SHORT & & $HIGH$ & & $PDHigh$ \\ - FS4: R2 OPEN & & $LOW$ & & $PDLow$ \\ \hline + FS10: PIN 2 $\stackrel{short}{\longrightarrow}$ PIN 3 & & A inputs shorted, & & \\ + & & output controlled by internal offset & & $LOW_A$ or $HIGH_A$ \\ \hline + FS11: PIN 3 $\stackrel{short}{\longrightarrow}$ PIN 4 & & A + input held to ground & & $LOW_A$ \\ \hline + FS12: PIN 5 $\stackrel{short}{\longrightarrow}$ PIN 6 & & B inputs shorted, & & \\ + & & output controlled by internal offset & & $LOW_B$ or $HIGH_B$ \\ \hline + FS13: PIN 6 $\stackrel{short}{\longrightarrow}$ PIN 7 & & B -ve 100\% Feed back, low gain & & $LOW_B$ \\ \hline + + FS14: PIN 7 $\stackrel{short}{\longrightarrow}$ PIN 8 & & B output held high & & $HIGH_B$ \\ \hline + \hline \end{tabular} @@ -293,19 +358,40 @@ these conditions. \end{table} +\clearpage + + + +\subsection{Comparing the component failure mode sources} + +EN298 pinouts failure mode technique. +For our OP-AMP example could have come up with different symptoms for both sides. Cannot predict the effect of internal errors, for instance ($LOW_{slew}$) +is missing from the EN298 failure modes set. + +% FMD-91 +% +% I have been working on two examples of determining failure modes of components. +% One is from the US military document FMD-91, where internal failures +% of components are described (with stats). +% +% The other is EN298 where the failure modes for generic component types are prescribed, or +% determined by a procedure where failure scenarios of all pins OPEN and all adjacent pins shorted +% is applied. These techniques +% +% The FMD-91 entries need, in some cases, some interpretation to be mapped to +% component failure symptoms, but include failure modes that can be due to internal failures. +% The EN298 SHORT/OPEN procedure cannot determine failures due to internal causes but can be applied to any IC. +% +% Could I come in and see you Chris to quickly discuss these. +% +% I hope to have chapter 5 finished by the end of March, chapter 5 being the +% electronics examples for the FMMD methodology. - - - - - - - - +\clearpage %%