robin/Robin_PHD
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

C Garret CH2 comments 13SEP2013

Browse Source
This commit is contained in:
Robin P. Clark 2013-09-13 15:39:06 +01:00
parent 96928dfca2
commit 7a78aa2646
1 changed files with 34 additions and 32 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

66
submission_thesis/CH2_FMEA/copy.tex
View File

@ -94,7 +94,7 @@ function that they perform.
The initial stage of the FMEA process is with the basic, or starting components.
%
These components are the sort bought in or considered as pre-assembled modules.
These are termed {\bcs}; they are considered ``atomic'' i.e. they are not broken down further.
These are termed `{\bcs}'; they are considered ``atomic'' i.e. they are not broken down further.
%
The first requirement for a {\bc} is to define the ways in which it can fail,
this relationship %between a {\bc} and its failure modes,
@ -177,7 +177,7 @@ can in some cases indicate how a component could fail/misbehave.
%under given conditions.
%
How %base
components could fail internally, is not of interest to an FMEA investigation.
components could fail internally is not of interest to an FMEA investigation.
The FMEA investigator needs to know what failure behaviour a component could exhibit. %, or in other words, its modes of failure.
%
A large body of literature exists giving guidance for the determination of component {\fms}.
@ -219,7 +219,7 @@ FIT claims for modern integrated micro-controllers are typically less than five~
%
The FMEA variant\footnote{EN61508 (and related standards) are based on the FMEA variant Failure Mode Effects and Diagnostic Analysis (FMEDA)}
used for European standard EN61508~\cite{en61508}
requires statistics for Meantime to Failure (MTTF) for all {\bc} failure modes.
requires statistics for Mean Time to Failure (MTTF) for all {\bc} failure modes.
% One is from the US military document FMD-91, where internal failures
@ -268,11 +268,11 @@ European burner standard EN298~\cite{en298}, are compared and contrasted.
\paragraph{Resistor failure modes according to FMD-91.}
\fmodegloss
The resistor is a ubiquitous component in electronics, and is therefore a good candidate for detailed examination of its failure modes.
%The resistor is a ubiquitous component in electronics, and is therefore a good candidate for detailed examination of its failure modes.
%
FMD-91\cite{fmd91}[3-178] lists many types of resistor
and lists many possible failure causes.
For instance for {\textbf{Resistor,~Fixed,~Film}} the following failure causes are given:
and lists many possible failure causes,
for instance for {\textbf{Resistor,~Fixed,~Film}} the following failure causes are given:
\begin{itemize}
\item Opened 52\% ,
\item Drift 31.8\% ,
@ -302,6 +302,8 @@ as listed below:
\item Lead damage 1.9\% $\mapsto$ OPEN.
\end{itemize}
%
The symptomatic descriptor chosen is based on experience and are not unique.
%
Note, that the main cause of resistor value drift is overloading. % of components.
This is borne out in the FMD-91~\cite{fmd91}[232] entry for a resistor network where the failure
modes do not include drift.
@ -364,7 +366,7 @@ include the failure mode DRIFT.
EN298 does not include this, mainly because it imposes circuit design constraints
that effectively side step that problem.
%
For this study the conservative view from EN298 is taken, and the failure
For this study the conservative view from EN298, but restrictive view from FMD-91 (i.e. no DRIFT) is taken, and the failure
modes for a generic resistor taken to be both OPEN and SHORT. The function $fm$ is used
to return a set of failure modes,
i.e.
@ -407,8 +409,8 @@ 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 12.5\%
\item Opened $V_+$ open 6.3\%
\item Shorted inputs (labelled $V_+$ to $V_-$), overstress, resistive short in amplifier 12.5\%
\item Opened input (labelled $V_+$) open 6.3\%
\end{itemize}
These are mostly internal causes of failure, more of interest to the component manufacturer
@ -428,7 +430,7 @@ This means that the op-amp will not react quickly to changes on its input termin
This is a failure symptom that may not be of concern in a slow responding system like an
instrumentation amplifier. However, where higher frequencies are being processed,
a signal may be lost entirely.
This failure cause can be mapped to a symptomatic {\fm} called $LOW_{slew}$.
This failure cause can be mapped to a symptomatic {\fm} called $LOW\_SLEW$.
\paragraph{No Operation - over stress.}
Here the OP-Amp has been damaged, and the output may be held HIGH or LOW, or may be
@ -445,13 +447,13 @@ This failure cause maps to $HIGH$ or $LOW$.
\paragraph{Open input: $V_+$.}
This failure cause will mean that the minus input will have the very high gain
of the Op-Amp applied to it, and the output will be forced HIGH or LOW.
This failure cause maps to $HIGH$ or $LOW$.
This failure cause maps to $HIGH$ or $LOW$.\footnote{No failure mode for open input $V_-$ was listed in this FMD-91 entry~\cite{fmd91}{3-116].}
\paragraph{Collecting Op-Amp failure modes from FMD-91.}
An Op-Amp's failure mode behaviour, under FMD-91 definitions will have the following {\fms}:
\begin{equation}
\label{eqn:opampfms}
fm(OpAmp) = \{ HIGH, LOW, NOOP, LOW_{slew} \} .
fm(OpAmp) = \{ HIGH, LOW, NOOP, LOW\_SLEW \} .
\end{equation}
@ -468,11 +470,11 @@ are examined and from this its {\fms} are determined.
%
% Collecting the op-amp failure modes from table ~\ref{tbl:lm358} we obtain the same {\fms}
% that we got from FMD-91, listed in equation~\ref{eqn:opampfms}, except for
% $LOW_{slew}$.
% $LOW\_SLEW$.
%
Collating the op-amp failure modes from table ~\ref{tbl:lm358} the same {\fms}
from FMD-91 are obtained---listed in equation~\ref{eqn:opampfms}---except for
$LOW_{slew}$.
$LOW\_SLEW$.
%\paragraph{EN298: Open and shorted pin failure symptom determination technique}
@ -507,23 +509,23 @@ $LOW_{slew}$.
& & 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
FS6: & & 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
FS8: & & (V+ supply) 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
FS9: PIN 1 $\stackrel{short}{\longrightarrow}$ PIN 2 & & A -ve 100\% Feed back, unity gain & & $LOW_A$ \\ \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
FS11: PIN 3 $\stackrel{short}{\longrightarrow}$ PIN 4 & & A + input held to ground & & $LOW_A$ or $HIGH_A$ \\ \hline
FS12: PIN 5 $\stackrel{short}{\longrightarrow}$ PIN 6 & & B inputs shorted, & & \\
& & output controlled by internal offset & & $LOW_B$ or $HIGH_B$ \\ \hline
@ -554,14 +556,14 @@ $LOW_{slew}$.
For the purpose of the examples to follow in this document, op-amp's
are assigned the following failure modes:
%
$$ fm(OPAMP) = \{ LOW, HIGH, NOOP, LOW_{slew} \} . $$
$$ fm(OPAMP) = \{ LOW, HIGH, NOOP, LOW\_SLEW \} . $$
%
\subsection{Comparing the component failure mode sources: EN298 vs FMD-91}
The EN298 pinouts failure mode technique cannot reveal failure modes due to internal failures,
and that is why it misses the $LOW_{slew}$.
and that is why it misses the $LOW\_SLEW$.
%
The FMD-91 entries for op-amps are not directly usable as
component {\fms} in FMEA and require interpretation.
@ -783,13 +785,13 @@ of the electronic circuit for each analysis.
\paragraph{Single component failure mode to system failure relation.}
%
%
% NEED SOME NICE HISTORICAL REFS HERE
FMEA, due to its inductive bottom-up approach, is good
at mapping potential single component failures to system level faults/events.
%
The concept of the unacceptability of a single component failure causing a system failure, % catastrophe,
The concept of the unacceptability of a single component failure causing a system failure % catastrophe,
is an important and easily understood measurement of safety.
%
They are easy to calculate
@ -1327,7 +1329,7 @@ or realistic levels of risk.
%
SIL levels are intended to
classify the statistical safety of installed plant:
salesmen’s terms such as a `SIL~3~sensor' or other `device' given a SIL level, are meaningless.
sales terms such as a `SIL~3~sensor' or other `device' given a SIL level, are meaningless.
%
SIL analysis is concerned with `safety~loops', not individual modules, sensors, computing devices or actuators.
%
@ -1449,13 +1451,13 @@ by statistically determining how frequently it can fail dangerously.
\section{FMEA used for Safety Critical Approvals}
\fmmdglossDFMEA
\subsection{DESIGN FMEA: Safety Critical Approvals FMEA}
\begin{figure}[h]
\centering
\includegraphics[width=300pt,keepaspectratio=true]{./CH2_FMEA/tech_meeting.png}
% tech_meeting.png: 350x299 pixel, 300dpi, 2.97x2.53 cm, bb=0 0 84 72
\caption{FMEA Meeting}
\label{fig:tech_meeting}
\end{figure}
% \begin{figure}[h]
% \centering
% \includegraphics[width=300pt,keepaspectratio=true]{./CH2_FMEA/tech_meeting.png}
% % tech_meeting.png: 350x299 pixel, 300dpi, 2.97x2.53 cm, bb=0 0 84 72
% \caption{FMEA Meeting}
% \label{fig:tech_meeting}
% \end{figure}
%Static FMEA, Design FMEA, Approvals FMEA
%
Experts from Approval House and Equipment Manufacturer
@ -1517,7 +1519,7 @@ potential strategies are listed below:
%
\begin{itemize}
\item Look at all components electronically adjacent (i.e. connected to the affected component),
\item Look at all components connected (as above) and those one removed (those connected to those connected to the affected component),
\item Look at all components connected (as above) and those once removed (those connected to those connected to the affected component),
\item Look at components forward of the {\fm} in the signal path,
\item Look at all components in the signal path,
\item Look at all components in the signal path including those one connection removed,