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AF comments on Chapter 4.

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Cannot now use the term symptom (but it is still useful to describe stuff
and John suggested its use ARRRRRGGGGGGGGGHHHHHHHHHH

Still need to sort out the DAGS

Feels like thrashing rather than re-writing
Changing things round for the sake of it
half of AF's comments just show ignorance of electronics or
are pedantic. Rarely do they HELP.
They just rip the thing apart.
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2
submission_thesis/CH4_FMMD/Makefile
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@ -1,6 +1,6 @@
PNG_DIA = cfg2.png cfg.png compco2.png compco3.png compco.png component.png componentpl.png fmmd_uml2.png fmmd_uml.png partitioncfm.png master_uml.png top_down_de_comp.png dc1.png dc2.png PNG_DIA = cfg2.png cfg.png compco2.png compco3.png compco.png component.png componentpl.png fmmd_uml2.png fmmd_uml.png partitioncfm.png master_uml.png top_down_de_comp.png dc1.png dc2.png eulerfmmd.png
%.png:%.dia %.png:%.dia

226
submission_thesis/CH4_FMMD/copy.tex
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@ -52,13 +52,29 @@
\section{Introduction} \section{Introduction}
This chapter This chapter
considers %starts with %an overview of current failure modelling techniques, and then starts with %starts with %an overview of current failure modelling techniques, and then
a worked example to introduce % using a worked example to introduce % using
the new methodology, the new methodology,
Failure Mode Modular De-composition (FMMD). Failure Mode Modular De-composition (FMMD).
This is followed by a discussion on the design of the FMMD methodology and then a This is followed by a discussion on the design of the FMMD methodology and then a
%an ontological %an ontological
description using UML class models. description using UML class models.
% This chapter defines the FMMD process and related concepts and calculations.
FMMD is in essence modularised FMEA. Rather than taking each component failure mode
and extrapolating top level or system failure symptoms from it,
small groups of components are collected into {\fgs} and analysed,
and then {\dcs} are used to represent the {\fgs}.
These {\dcs} are used to then build further {\fgs} until a hierarchy of {\fgs}
and {\dcs} has been built, converging to a final {\dc}
at the top of the hierarchy.
%
Or in other words we take the traditional FMEA process, and modularise it.
We break down each stage of reasoning
into small manageable groups, and use the results of those groups, as {\dcs}
to build higher level groups.
% %This has advantages of concentrating
% %effort in where modules interact,
%A notation is then described to index and classify objects created in FMMD hierarchical models. %A notation is then described to index and classify objects created in FMMD hierarchical models.
@ -453,11 +469,9 @@ description using UML class models.
To demonstrate the principles behind FMMD, we use it to analyse a To demonstrate the principles of FMMD, we use it to analyse a
commonly used circuit, the non-inverting op amp~\cite{aoe}[p.234], shown in figure \ref{fig:noninvamp}. commonly used circuit, the non-inverting op amp~\cite{aoe}[p.234], shown in figure \ref{fig:noninvamp}.
%
\begin{figure}[h+] \begin{figure}[h+]
\centering \centering
%\includegraphics[width=100pt,keepaspectratio=true]{../../noninvopamp/noninv.png} %\includegraphics[width=100pt,keepaspectratio=true]{../../noninvopamp/noninv.png}
@ -466,21 +480,22 @@ commonly used circuit, the non-inverting op amp~\cite{aoe}[p.234], shown in fig
\caption{Standard non inverting amplifier configuration} \caption{Standard non inverting amplifier configuration}
\label{fig:noninvamp} \label{fig:noninvamp}
\end{figure} \end{figure}
%
The function of the resistors in this circuit is to set the amplifier gain. The function of the resistors in this circuit is to set the amplifier gain.
They operate as a potential divider\footnote{The resistors act as a potential divider assuming the op-amp has high impedance.} They operate as a potential divider, the resistors act as a potential divider assuming the op-amp has high impedance,
and program the inverting input on the op-amp and program the inverting input on the op-amp
to balance them against the positive input, giving the voltage gain ($G_v$) to balance them against the positive input, giving the voltage gain ($G_v$)
defined by $ G_v = 1 + \frac{R2}{R1} $ at the output. defined by $ G_v = 1 + \frac{R2}{R1} $ at the output.
\subsection{Potential Divider.} \paragraph{Potential Divider.}
\label{subsec:potdiv} \label{subsec:potdiv}
As the resistors work to provide a specific function, that of a potential divider, As the resistors work to provide a specific function, that of a potential divider,
we can treat them as a collection of components with a specific functionality---which can be termed a `{\fg}'. we can treat them as a collection of components with a specific functionality---which can be termed a `{\fg}'.
This {\fg} has two members, $R1$ and $R2$. This {\fg} has two members, $R1$ and $R2$.
Taken as an entity the potential divider can be viewed as a {\dc}.
That is to say we can treat the potential divider, comprised of two resistors
to act as a component.
% %
Using the EN298 specification for resistor failure~\cite{en298}[App.A], Using the EN298 specification for resistor failure~\cite{en298}[App.A],
we can assign failure modes of $OPEN$ and $SHORT$ to the resistors individually (assignment of failure modes we can assign failure modes of $OPEN$ and $SHORT$ to the resistors individually (assignment of failure modes
@ -507,7 +522,7 @@ We represent a resistor and its failure modes as a directed acyclic graph (DAG)
\label{fig:rdag} \label{fig:rdag}
\end{figure} \end{figure}
Thus $R1$ has failure modes $\{R1\_OPEN, R1\_SHORT\}$ and $R2$ has failure modes $\{R2\_OPEN, R2\_SHORT\}$. Thus $R1$ has failure modes $\{R1_{OPEN}, R1_{SHORT}\}$ and $R2$ has failure modes $\{R2_{OPEN}, R2_{SHORT}\}$.
% %
We look at each of these base component failure modes, We look at each of these base component failure modes,
and determine how they affect the operation of the potential divider. and determine how they affect the operation of the potential divider.
@ -522,7 +537,11 @@ Each {\fc} is analysed to determine the `symptom'
of the potential dividers' operation. For instance of the potential dividers' operation. For instance
if resistor $R_1$ were to become open, then the potential~divider would not be grounded and the if resistor $R_1$ were to become open, then the potential~divider would not be grounded and the
voltage output from it would float high (+ve). voltage output from it would float high (+ve).
This would mean the symptom of the failed potential divider would be voltage high output. %We can now consider the {\fg} This would mean the symptom of the failed potential divider would be voltage high output.
%
The failure symptom of a high potential divider output is termed `HighPD', and
for it outputing a low voltage `LowPD'. % Andrew asked for this to be defined before the table. ...
%We can now consider the {\fg}
%as a component in its own right, and its symptoms as its failure modes. %as a component in its own right, and its symptoms as its failure modes.
{ \small { \small
@ -531,8 +550,8 @@ This would mean the symptom of the failed potential divider would be voltage hig
\centering % used for centering table \centering % used for centering table
\begin{tabular}{||l|c|c|l||} \begin{tabular}{||l|c|c|l||}
\hline \hline \hline \hline
\textbf{Fault} & \textbf{Pot.Div} & \textbf{Symptom} \\ \textbf{Fault} & \textbf{Pot.Div} & \textbf{Derived Component} \\ % \textbf{Symptom} \\
\textbf{Scenario} & \textbf{Effect} & \textbf{Description} \\ \textbf{Mode} & \textbf{Effect} & \textbf{Failure modes} \\ %\textbf{Description} \\
% R & wire & res + & res - & description % R & wire & res + & res - & description
\hline \hline
\hline \hline
@ -547,17 +566,22 @@ This would mean the symptom of the failed potential divider would be voltage hig
} }
\vbox{ %\vbox{
From table \ref{tbl:pdfmea} we can see that the resistor From table \ref{tbl:pdfmea} we can see that the resistor
failures modes lead to some common symptoms. failures modes lead to some common symptoms of failure from the perspective of the {\fg}.
These common symptoms are an important concept for FMMD. %YOU FUCKING CUNTS, TELL ME TO USE THE TERM SYMPTOM AND THEN TELL ME TO FUCKING REMOVE IT A YEAR LATER> CUNTS
It means that we can take multiple failure modes from a {\fg} and resolve them %symptoms.
to a a common symptom. This means that we simplify the FMEA analysis task for further stages. These common symptoms of failure are an important concept for FMMD.
By drawing directed edges from the failure modes to the symptoms, It means that we can take multiple failure modes from {\fgs} components and resolve them
we can show the relationships between the component failure modes and resultant symptoms. to failure modes of the {\fg}.
%
This means that we simplify the FMEA analysis task for further stages.
By drawing directed edges from the failure modes to the {\dc} failure modes, % symptoms,
we show the relationships between the component failure modes and
{\dc} failure modes. % resultant symptoms.
%The {\fg} can now be considered a derived component. %The {\fg} can now be considered a derived component.
This is represented in the DAG in figure \ref{fig:fg1adag}. This is represented in the DAG in figure \ref{fig:fg1adag}.
} %}
\begin{figure}[h] \begin{figure}[h]
\centering \centering
@ -569,14 +593,14 @@ This is represented in the DAG in figure \ref{fig:fg1adag}.
\tikzstyle{symptom}=[fmmde, fill=blue!50]; \tikzstyle{symptom}=[fmmde, fill=blue!50];
\tikzstyle{annot} = [text width=4em, text centered] \tikzstyle{annot} = [text width=4em, text centered]
\node[component] (R1) at (0,-0.7) {$R_1$}; \node[component] (R1) at (0,-1.0) {$R_1$};
\node[component] (R2) at (0,-1.9) {$R_2$}; \node[component] (R2) at (0,-3.0) {$R_2$};
\node[failure] (R1SHORT) at (\layersep,-0) {$R1_{Sh}$}; \node[failure] (R1SHORT) at (\layersep,-0) {$R1_{SHORT}$};
\node[failure] (R1OPEN) at (\layersep,-1.1) {$R1_{Op}$}; \node[failure] (R1OPEN) at (\layersep,-1.8) {$R1_{OPEN}$};
\node[failure] (R2SHORT) at (\layersep,-2.4) {$R2_{Sh}$}; \node[failure] (R2SHORT) at (\layersep,-3.4) {$R2_{SHORT}$};
\node[failure] (R2OPEN) at (\layersep,-3.7) {$R2_{Op}$}; \node[failure] (R2OPEN) at (\layersep,-5.2) {$R2_{OPEN}$};
\path (R1) edge (R1SHORT); \path (R1) edge (R1SHORT);
\path (R1) edge (R1OPEN); \path (R1) edge (R1OPEN);
@ -586,8 +610,8 @@ This is represented in the DAG in figure \ref{fig:fg1adag}.
% Potential divider failure modes % Potential divider failure modes
% %
\node[symptom] (PDHIGH) at (\layersep*2,-0.7) {$PD_{HIGH}$}; \node[symptom] (PDHIGH) at (\layersep*2,-1.0) {$PD_{HIGH}$};
\node[symptom] (PDLOW) at (\layersep*2,-2.2) {$PD_{LOW}$}; \node[symptom] (PDLOW) at (\layersep*2,-3.0) {$PD_{LOW}$};
\path (R1OPEN) edge (PDHIGH); \path (R1OPEN) edge (PDHIGH);
\path (R2SHORT) edge (PDHIGH); \path (R2SHORT) edge (PDHIGH);
@ -602,23 +626,25 @@ This is represented in the DAG in figure \ref{fig:fg1adag}.
\end{figure} \end{figure}
We can now formulate a `derived component' to represent this potential divider: We can now create % formulate
a `derived component' to represent this potential divider:
we name this \textbf{PD}. we name this \textbf{PD}.
This {\dc} will have two failure modes. This {\dc} will have two failure modes.
We use the symbol $\derivec$ to represent the process of taking the analysed We use the symbol $\derivec$ to represent the process of taking the analysed
{\fg} and creating from it a {\dc}. The creation of the {\dc} \textbf{PD} is {\fg} and creating from it a {\dc}.
represented in figure~\ref{fig:dc1}. %The creation of the {\dc} \textbf{PD} isrepresented in figure~\ref{fig:dc1}.
We represent the {\dc} \textbf{PD}, as a DAG in figure \ref{fig:dc1dag}. We represent the {\dc} \textbf{PD}, as a DAG in figure \ref{fig:dc1dag}.
%We could represent it algebraically thus: $ \derivec(PotDiv) = %We could represent it algebraically thus: $ \derivec(PotDiv) =
\begin{figure}[h+] % FUCKING HELL THIS IS REMOVED TOO : CUNTS
\centering % \begin{figure}[h+]
\includegraphics[width=200pt,keepaspectratio=true]{./CH4_FMMD/dc1.png} %%% Where the f**king hell is this file ????? in an old paper even in the SYSSAFE2011 % \centering
% dc1.jpg: 430x619 pixel, 72dpi, 15.17x21.84 cm, bb=0 0 430 619 % \includegraphics[width=200pt,keepaspectratio=true]{./CH4_FMMD/dc1.png} %%% Where the f**king hell is this file ????? in an old paper even in the SYSSAFE2011
\caption{From functional group to derived component} % % dc1.jpg: 430x619 pixel, 72dpi, 15.17x21.84 cm, bb=0 0 430 619
\label{fig:dc1} % \caption{From functional group to derived component}
\end{figure} % \label{fig:dc1}
% \end{figure}
% We can now represent the potential divider as a {\dc}. % We can now represent the potential divider as a {\dc}.
@ -641,7 +667,7 @@ We represent the {\dc} \textbf{PD}, as a DAG in figure \ref{fig:dc1dag}.
\path (PD) edge (PDHIGH); \path (PD) edge (PDHIGH);
\path (PD) edge (PDLOW); \path (PD) edge (PDLOW);
\end{tikzpicture} \end{tikzpicture}
\caption{DAG representing a Potential Divider (PD) its failure symptoms} \caption{DAG representing the {\dc} Potential Divider (PD) and its failure modes.}
\label{fig:dc1dag} \label{fig:dc1dag}
\end{figure} \end{figure}
@ -698,7 +724,7 @@ We can represent these failure modes on a DAG (see figure~\ref{fig:op1dag}).
%} %}
%\clearpage %\clearpage
%\paragraph{Modelling the OP amp with the potential divider.} %\paragraph{Modelling the OP amp with the potential divider.}
We now collect the OP amp and the {\dc} {\em PD}, to We now collect the OP amp and the {\dc} {\em PD} to % andrew critised this sentence but it made sense to Chris and I
form a {\fg} to represent the non-inverting amplifier. form a {\fg} to represent the non-inverting amplifier.
% %
%We have the failure modes of the {\dc} for the potential divider, %We have the failure modes of the {\dc} for the potential divider,
@ -708,8 +734,9 @@ form a {\fg} to represent the non-inverting amplifier.
%by bringing together the failure modes from \textbf{opamp} and \textbf{PD}. %by bringing together the failure modes from \textbf{opamp} and \textbf{PD}.
% %
The two components in this new {\fg} have failure modes. The two components in this new {\fg} have failure modes.
Each of these failure modes will be given a {\fc} for analysis, %Each of these failure modes will be given a {\fc} for analysis,
and this is represented in table \ref{tbl:ampfmea1}. %and this is represented in table \ref{tbl:ampfmea1}.
% CUNTS NOW I CANNOT USE THE TERM FAILURE SCENARIO---was first column of table below
%\clearpage %\clearpage
{\footnotesize {\footnotesize
@ -718,13 +745,13 @@ and this is represented in table \ref{tbl:ampfmea1}.
\centering % used for centering table \centering % used for centering table
\begin{tabular}{||l|c|c|l||} \begin{tabular}{||l|c|c|l||}
\hline \hline \hline \hline
\textbf{Fault} & \textbf{Amplifier} & \textbf{Symptom} \\ \textbf{Fault} & \textbf{Amplifier} & \textbf{Derived component} \\ %Symptom} \\
\textbf{Scenario} & \textbf{Effect} & \textbf{Description} \\ \textbf{Mode} & \textbf{Effect} & \textbf{Failure Modes} \\ %Description} \\
% R & wire & res + & res - & description % R & wire & res + & res - & description
\hline \hline
\hline \hline
FS1: $OPAMP$ & Output & AMPHigh \\ FS1: $OPAMP$ & Output & AMPHigh \\
LatchUP & High & \\ \hline LatchUP & High & \\ \hline
FS2: $OPAMP$ & Output Low& AMPLow \\ FS2: $OPAMP$ & Output Low& AMPLow \\
LatchDown & Low gain & \\ \hline LatchDown & Low gain & \\ \hline
@ -784,11 +811,11 @@ and this is represented in table \ref{tbl:ampfmea1}.
\node[failure] (OPAMPNP) at (\layersep,-2.5) {noop}; \node[failure] (OPAMPNP) at (\layersep,-2.5) {noop};
\node[failure] (OPAMPLS) at (\layersep,-3.8) {lowslew}; \node[failure] (OPAMPLS) at (\layersep,-3.8) {lowslew};
\node[failure] (R1SHORT) at (\layersep,-5.1) {$R1_{Sh}$}; \node[failure] (R1SHORT) at (\layersep,-5.1) {$R1_{SHORT}$};
\node[failure] (R1OPEN) at (\layersep,-6.4) {$R1_{Op}$}; \node[failure] (R1OPEN) at (\layersep,-6.4) {$R1_{OPEN}$};
\node[failure] (R2SHORT) at (\layersep,-7.7) {$R2_{Sh}$}; \node[failure] (R2SHORT) at (\layersep,-7.7) {$R2_{SHORT}$};
\node[failure] (R2OPEN) at (\layersep,-9.0) {$R2_{Op}$}; \node[failure] (R2OPEN) at (\layersep,-9.0) {$R2_{OPEN}$};
@ -876,31 +903,57 @@ and this is represented in table \ref{tbl:ampfmea1}.
%amplification characteristics from FS2 and FS6 can be considered as low output from the OPAMP for the application %amplification characteristics from FS2 and FS6 can be considered as low output from the OPAMP for the application
%in hand (say milli-volt signal amplification). %in hand (say milli-volt signal amplification).
For this amplifier configuration we have three failure modes; {\em AMP\_High, AMP\_Low, LowPass}. % see figure~\ref{fig:fgampb}. % For this amplifier configuration we have three {\dc} failure modes; {\em AMP\_High, AMP\_Low, LowPass}. % see figure~\ref{fig:fgampb}.
This model now has two stages of analysis hierarchy, as represented in figure~\ref{fig:dc2}. % This model now has two stages of analysis hierarchy,
% as represented in figure~\ref{fig:dc2}.
%
From the analysis in table \ref{tbl:ampfmea1} we can create the {\dc} {\em NONINVAMP}, which From the analysis in table \ref{tbl:ampfmea1} we can create the {\dc} {\em NONINVAMP}, which
represents the failure mode behaviour of the non-inverting amplifier. represents the failure mode behaviour of the non-inverting amplifier.
% \begin{figure}[h]
% \centering
% \includegraphics[width=225pt]{./CH4_FMMD/dc2.png}
% % dc2.png: 635x778 pixel, 72dpi, 22.40x27.45 cm, bb=0 0 635 778
% \caption{Hierarchy representing the two stage FMMD analysis of the non-inverting amplifier}
% \label{fig:dc2}
% \end{figure}
We can represent the hierarchy as an Euler diagram as well, where the curves
define the components and {\dcs} used to form {\fgs}, see figure~\ref{fig:eulerfmmd}.
\begin{figure}[h] \begin{figure}[h]
\centering \centering
\includegraphics[width=225pt]{./CH4_FMMD/dc2.png} \includegraphics[width=300pt]{./CH4_FMMD/eulerfmmd.png}
% dc2.png: 635x778 pixel, 72dpi, 22.40x27.45 cm, bb=0 0 635 778 % eulerfmmd.png: 413x207 pixel, 72dpi, 14.57x7.30 cm, bb=0 0 413 207
\caption{Hierarchy representing the two stage FMMD analysis of the non-inverting amplifier} \caption{FMMD analysis of the INVAMP represented as an Euler diagram, showing the relationships between base and derived components.}
\label{fig:dc2} \label{fig:eulerfmmd}
\end{figure} \end{figure}
We can now examine the failure mode relationships in the {\dc} {\em INVAMP} by drawing it as a DAG. We can now examine the failure mode relationships in the {\dc} {\em INVAMP} by drawing it as a DAG.
%expand the {\em PD} {\dc} and have a full FMMD failure %mode %expand the {\em PD} {\dc} and have a full FMMD failure %mode
%model %model
We can traverse this DAG, tracing the top level symptoms down to the leaves of the tree (the leaves being {\bc} failure modes), We can traverse this DAG, tracing the top level % symptoms
failure modes
down to the base component failure modes, %leaves of the tree (the leaves being {\bc} failure modes),
and thus determine all possible causes for and thus determine all possible causes for
the three high level symptoms, i.e. the failure~modes of the non-inverting amplifier {\em INVAMP}. the three high level symptoms, i.e. the failure~modes of the non-inverting amplifier {\dc} {\em INVAMP}.
Knowing all possible causes for a top level event/failure~mode Knowing all possible causes for a top level event/failure~mode
is extremely useful. Were the top level event to be classified as catastrophic for instance, we could use this information is extremely useful. Were the top level event to be classified as catastrophic for instance,
to strengthen components that could cause the top level event/failure. we could use this information
to strengthen components that could cause that particular top level event/failure.
% %
Figure \ref{fig:noninvdag1} shows a fully expanded DAG, from which we can derive information Figure \ref{fig:noninvdag1} shows a DAG,
to assist in building models for FTA, FMEA, FMECA and FMEDA failure mode analysis methodologies. from which we can trace top level failure modes to the base component failure modes
that can cause them.
That is to say that we can trace failure mode effects
from base component level to the top and vice versa.
%
Having a base component failure modes traceable to top event events,
provides a a failure mode model, from which
we can derive information
to assist in building models for FTA, FMEA, FMECA, FMEDA
and other failure mode analysis methodologies.
@ -961,7 +1014,7 @@ Base Component & An atomic building block used at the lowest level of an FMMD mo
{\em Constraint} & This object must have a defined set of failure~modes. \\ \hline {\em Constraint} & This object must have a defined set of failure~modes. \\ \hline
Component & A building block, this may be a {\bc} or a {\dc} or manufacturers part. \\ Component & A building block, this may be a {\bc} or a {\dc}. \\%or manufacturers part. \\
{\em Constraint} & This object must have a defined set of failure~modes. \\ \hline {\em Constraint} & This object must have a defined set of failure~modes. \\ \hline
@ -977,8 +1030,8 @@ Functional Grouping & A collection of
components with a functional purpose. components with a functional purpose.
\\ \hline \\ \hline
Symptom & A failure symptom of a {\fg}, caused by % WHICH MUST BE UNIQUE AND SEPARATE WITHIN THE \fg % Symptom & A failure symptom of a {\fg}, caused by % WHICH MUST BE UNIQUE AND SEPARATE WITHIN THE \fg
a combination of its component failure modes. \\ \hline % a combination of its component failure modes. \\ \hline
Derived Component & A theoretical component, created to represent the failure Derived Component & A theoretical component, created to represent the failure
@ -990,8 +1043,8 @@ Derived Component & A theoretical component, created to represent the failure
Unitary State & A component with `unitary~state' failure modes, means that it cannot fail Unitary State & A component with `unitary~state' failure modes, means that it cannot fail
with more than one of its failure modes at a time.\\ \hline with more than one of its failure modes at a time.\\ \hline
Failure Scenario & A single failure mode (or a combination), used to % Failure Scenario & A single failure mode (or a combination), used to
determine failure mode effects on a {\fg}. % determine failure mode effects on a {\fg}.
\\ \\
\hline \hline
@ -1009,18 +1062,19 @@ like an %integrated
micro-controller/servo motor, or quite simple like the resistor. micro-controller/servo motor, or quite simple like the resistor.
% %
We %can We %can
identify a usually identify a
component by its name, a manufacturer's part number and perhaps component by its name, a manufacturer's part number and perhaps
a vendor's reference number. a vendor's reference number. %In a controlled production evironment
%
Geoffrey Hall, writing in Spacecraft Systems Engineering~\cite{scse}[p.619] Geoffrey Hall, writing in Spacecraft Systems Engineering~\cite{scse}[p.619]
defines a `part' thus defines a `part' thus
``{{Part(definition)}---The lowest level of assembly, beyond which further disassembly irrevocably destroys the item''. ``{{Part(definition)}---The lowest level of assembly, beyond which further disassembly irrevocably destroys the item''.
This definition of a `part' is useful, but consider parts, such as quad packaged op-amps.
% %
Here we have four op-amps on one chip. For FMEA we would consider each op-amp in the package This definition of a `part' is useful, but consider parts, such as quad packaged op-amps:
as a separate building block for a circuit. %
in this case, we have four op-amps on one chip. For FMEA we would consider each op-amp in the package
as a separate building block for a circuit. For FMMD each of these four op-amps
in the chip would be considered to be a separate {\bc}.
% CAN WE FIND SUPPORT FOR THIS IN LITERATURE??? % CAN WE FIND SUPPORT FOR THIS IN LITERATURE???
% %
We, in fact, need to go a little further than the above definition of a part, We, in fact, need to go a little further than the above definition of a part,
@ -1035,7 +1089,7 @@ Both op-amps and transistors have published statistical failure rates and yet an
However, a circuit designer would usually consider individual transistors and individual op-amps However, a circuit designer would usually consider individual transistors and individual op-amps
as lowest level building blocks. as lowest level building blocks.
% %
In fact any component with published failure modes could be considered to be a {\bc}, In fact any lowest level building block with published failure modes could be considered to be a {\bc},
but this determination is the choice of the analyst, which may be influenced by the particular but this determination is the choice of the analyst, which may be influenced by the particular
standard~\cite{en298}~\cite{en61508} %~\cite{en230} standard~\cite{en298}~\cite{en61508} %~\cite{en230}
to which we are approving/analysing a system. to which we are approving/analysing a system.
@ -1051,9 +1105,9 @@ to which we are approving/analysing a system.
%000000elpful here to define the terms, `system', `functional~group', `component', `base~component', `symptom' and `derived~component/sub-system'. %000000elpful here to define the terms, `system', `functional~group', `component', `base~component', `symptom' and `derived~component/sub-system'.
%These are listed in table~\ref{tab:symexdef}. %These are listed in table~\ref{tab:symexdef}.
A system, is any coherent entity that would be sold as a product. % safety critical product. A system, is any coherent piece of equipment that performs a given task. % safety critical product.
% %
A component is a system that is a part of some larger system. A component can be viewed as a sub-system that is a part of some larger system.
% %
A modular system common to many homes is the sound separates audio system or stereo hi-fi. A modular system common to many homes is the sound separates audio system or stereo hi-fi.
% %
@ -1079,14 +1133,14 @@ for each `component'.
% %
If we look at the sound system example, If we look at the sound system example,
the CD~player could fail in several distinct ways, the CD~player could fail in several distinct ways,
and this could have been caused by a number of {\textbf{the CD players internal}} component failure modes. and this could have been caused by a number of {{the CD players internal}} component failure modes.
%no matter what has happened to it or has gone wrong inside it. %no matter what has happened to it or has gone wrong inside it.
% %
Using the reasoning that working from the bottom up forces the consideration of all possible Using the reasoning that working from the bottom up forces the consideration of all possible
component failures (which can be missed in a top~down approach \cite{faa}[Ch.9]), component failures (which can be missed in a top~down approach \cite{faa}[Ch.9]),
we are presented with a problem. Which initial collections of base components should we choose? we are presented with a problem: which initial collections of base components should we choose?
% %
For instance in the CD~player example; if we start at the bottom, we are presented with For instance in the CD~player example, if we start at the bottom, we are presented with
a massive list of base~components, resistors, motors, user~switches, laser~diodes, etc. a massive list of base~components, resistors, motors, user~switches, laser~diodes, etc.
Clearly, working from the bottom~up, we need to pick small Clearly, working from the bottom~up, we need to pick small
collections of components that work together in some way. collections of components that work together in some way.
@ -1161,7 +1215,8 @@ Currently, failure mode information is generally only available for generic com
%What components all have in common is that they can fail, and fail in a %What components all have in common is that they can fail, and fail in a
% number of well defined ways. % number of well defined ways.
For common {\bcs} For common {\bcs}
there is established literature for the failure modes for the system designer to consider (often with accompanying statistical there is established literature for the failure modes for the system designer to consider
(often with accompanying statistical
failure rates)~\cite{mil1991,en298,fmd91}. failure rates)~\cite{mil1991,en298,fmd91}.
% %
For instance, a simple resistor is generally considered For instance, a simple resistor is generally considered
@ -1330,11 +1385,14 @@ A flat set is a set containing just the failure modes and not sets of failure mo
%In practical term each component failure mode is considered as a `failure~scenario' or 'test~case' %In practical term each component failure mode is considered as a `failure~scenario' or 'test~case'
%for the {\fg}. %for the {\fg}.
% %
Each of these failure modes, and optionally combinations of them, are Each of these failure modes %, and optionally combinations of them, are
formed into failure~scenarios which are %formed into failure~scenarios which
are
analysed for their effect on the failure mode behaviour of the `{\fg}'. analysed for their effect on the failure mode behaviour of the `{\fg}'.
% %
Once we have the failure mode behaviour of the {\fg}, we can determine its symptoms of failure. Once we have the failure mode behaviour of the {\fg}, we can determine its symptoms of failure.
%,
%or the failure modes of the {\dc}.
%for the {\fg}. %for the {\fg}.
% %
We view these symptoms as derived failure modes of the {\fg}. We view these symptoms as derived failure modes of the {\fg}.

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