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symptom_ex_process/symptom_ex_process.tex
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@ -7,29 +7,25 @@ its component parts.
%, and the failure modes of those parts.
The technique uses a graphical notation, based on Euler\cite{eulerviz} and Constraint
diagrams\cite{constraint} to model failure modes and failure mode common symptom collection.
The technique is designed for making building blocks for a hierarchical fault model.
%The technique uses a graphical notation, based on Euler\cite{eulerviz} and Constraint diagrams\cite{constraint} to model failure modes and failure mode common symptom collection. The technique is designed for making building blocks for a hierarchical fault model.
Once the failure modes have been determined for a sub-system,
that sub-system may be treated as a `component' or `black box' and used
in conjunction with other such analysed sub-systems, to model
higher level sub-systems. In this way a hierarchy to represent the fault behaviour
of a system can be built.
%FMMD hierarchy
The hierarchy is built from the bottom up.
Starting with component failure modes at the bottom.
Because the process is bottom-up, syntax checking and tracking can ensure that
no component failure mode can be overlooked.
Once a hierarchy is in place it can be converted into a fault data model.
%
From the fault data model, automatic generation
of FTA\cite{nasafta} (Fault Tree Analysis) and mimimal cuts sets\cite{nucfta} are possible.
Also statistical reliability\cite{en61508} and MTTF (Mean Time to Failure) calculations can be produced
automatically, where component failure mode statistics are available\cite{mil1991}.
%
This paper focuses on the process of building the blocks that are used in the hierarchy.
\end{abstract}
@ -100,7 +96,7 @@ A sub-system will be composed of component parts, which
may themselves be sub-systems. However each `component part'
will have a fault/failure behaviour and it should
always be possible to obtain a set of failure modes
for each `component'.
for each `component'. In FMMD terms a sub-system is a derived component.
If we look at the sound system again as an
example; the CD~player could fail in serveral distinct ways, no matter
@ -153,7 +149,7 @@ Currently this sort of information is generally only available for generic comp
System & A product designed to \\
& work as a coherent entity \\ \hline
Sub-system & A part of a system, \\
& sub-systems may contain sub-systems \\ \hline
-or- derived component & sub-systems may contain sub-systems \\ \hline
Failure mode & A way in which a System, \\
& Sub-system or component can fail \\ \hline
Functional Group & A collection of sub-systems and/or \\
@ -173,73 +169,43 @@ Base Component & Any bought in component, which \\
\paragraph{symptom abstraction described}
The objective of `symptom abstraction' is to analyse the functional~group and find out what will happen to it,
when specified component failure modes occur.
Once we know how it fails as a functional~group, we can treat it as a component or sub-system
The objective of `symptom abstraction' is to analyse the functional~group and find
how it can fail
when specified components within it fail.
Once we know how functional~group can fail, we can treat it as a component or sub-system
with its own set of failure modes.
\paragraph{FMEA applied to the functional Group}
As the functional~group is a set of components, the failure~modes
that we have to consider are all the failure modes of its components.
Each failure mode (or combination of) investigated is termed a `test case'.
Each `test case' is analysed.
The component failure modes are examined with respect to their effect on the functional~group.
\paragraph{Symptom identification and collection}
When all `test~cases' have been analysed a second phase is applied.
%
This looks at the results of the `test~cases' as symptoms
of the sub-system.
In this way `test~case~results' are grouped as common symptoms, from the perspective of the sub-system.
To go back to the CD~player example, a failed
of the sub-system.
Single component failures within the functional~group may cause unique symptoms.
However, many failures, when looked at from the perspective of the functional group, will have the same symptoms.
These can be collected as `common symptoms'.
To go back to the CD~player example, a failed
output stage, and a failed internal audio amplifier,
will both cause the same failure; $no\_sound$ !
\paragraph{Collection of Symptoms}
The common symptoms of failure are identified and collected.
we can now consider the functional~group as a component and the common symptoms as its failure modes.
\paragraph{symptom abstraction represented on the diagram}
This process can be applied using a diagram.
From the collection of parts for the sub-system under analysis, a set of failure
modes for each component is obtained. A diagram is then drawn with
each component failure mode represented by a contour.
Component failure mode combinations are
chosen for `test cases'.\footnote{Combinations of component failure modes can be represented by overlapping contours}
A `test case' is represented on the diagram as a point or asterisk,
in a region enclosed by the contours representing the failure modes it investigates.
The effect on the sub-system of each test case is analysed.
%It is then represented on the diagram by an asterisk on the contour representing the failure mode.
The `test~case~results' are archived.
When all test cases have been analysed, we switch our attention to a higher abstraction level.
% We treat the sub-system as a black box, or as a component part itsself.
% We can now look at the test case results from the perspective of a `user'
% of this sub-system.
%
%
% \paragraph{symptom abstraction represented on the diagram} This process can be applied using a diagram. From the collection of parts for the sub-system under analysis, a set of failure modes for each component is obtained. A diagram is then drawn with each component failure mode represented by a contour. Component failure mode combinations are chosen for `test cases'.\footnote{Combinations of component failure modes can be represented by overlapping contours} A `test case' is represented on the diagram as a point or asterisk, in a region enclosed by the contours representing the failure modes it investigates. The effect on the sub-system of each test case is analysed. %It is then represented on the diagram by an asterisk on the contour representing the failure mode. The `test~case~results' are archived. When all test cases have been analysed, we switch our attention to a higher abstraction level. % We treat the sub-system as a black box, or as a component part itsself. % We can now look at the test case results from the perspective of a `user' % of this sub-system. % %
% We treat the sub-system as a `black box' and view the effects of the component failure
% at the sub-system level. This mean we are not interested so much in what the compoent does,
% but how the sub-system reacts when it fails in a certain way.
%
% Each `test case' is labelled from the perspective of the failure as seen at sub-system level.
%
We can now try to simplfy by determining common symptoms.
A common symptom, in this context, is defined as faults caused by different
component failure modes that have the same effect from the perspective
of a `user' of the sub-system.
Test case results can now viewed as failure modes of the sub-sytem or `black box', and grouped together
where there are common symptoms.
These are grouped together by joining them with lines. These lines form collected groups (or `spiders').
See figure \ref{fig:gensubsys3}.
%
It can be seen now that each {\em lone test case} and {\em spider} on the
diagram is a distinct failure mode of the sub-system.
This means that these failure modes represent the fault behaviour of the sub-system.
We can now treat this sub-system as a component in its own right, or in other words,
we have derived a failure mode model at a higher level of abstraction.
We can now draw a new diagram to represent the failure modes of the sub-system.
Each spider or lone test case, becomes a contour representing a failure mode
of the sub-system in this new diagram (see figure \ref{fig:gensubsys4}.
% We can now try to simplfy by determining common symptoms. A common symptom, in this context, is defined as faults caused by different component failure modes that have the same effect from the perspective of a `user' of the sub-system. Test case results can now viewed as failure modes of the sub-sytem or `black box', and grouped together where there are common symptoms. These are grouped together by joining them with lines. These lines form collected groups (or `spiders'). See figure \ref{fig:gensubsys3}.
% It can be seen now that each {\em lone test case} and {\em spider} on the diagram is a distinct failure mode of the sub-system. This means that these failure modes represent the fault behaviour of the sub-system. We can now treat this sub-system as a component in its own right, or in other words, we have derived a failure mode model at a higher level of abstraction. We can now draw a new diagram to represent the failure modes of the sub-system. Each spider or lone test case, becomes a contour representing a failure mode of the sub-system in this new diagram (see figure \ref{fig:gensubsys4}.
\section{The Process : To analyse a base level sub-system}
@ -249,15 +215,14 @@ To sumarise:
\item Determine a minimal functional group
\item Obtain list of components in the functional group
\item Collect the failure modes for each component
\item Draw these as contours on a diagram
\item Where multiple failures are examined use overlapping contours
\item For each region on the diagram, make a test case
\item Examine each test case and determine the effect of the component failure modes on the behaviour of the functional group
% \item Draw these as contours on a diagram
% \item Where si,ultaneous failures are examined use overlapping contours
% \item For each region on the diagram, make a test case
\item Examine each failure mode of all the components in the functional~group, and determine its effect on the failure behaviour of the functional group
\item Collect common symptoms. Imagine you are handed this functional group as a `black box', a sub-system to use.
Determine which test cases produce the same fault symptoms. Join common symptoms with lines connecting them (sometimes termed a `spider').
\item The lone test cases and the spiders are now the fault mode behaviour of the sub-system.
\item A new diagram can now be drawn where each spider, or lone test case from the original diagram
is represented as a contour. These contours represent the failure modes of the sub-system.
Determine which test cases produce the same fault symptoms.% Join common symptoms with lines connecting them (sometimes termed a `spider').
\item The lone test cases and the common~symptoms are now the fault mode behaviour of the sub-system/derived~component.
\item A new `derived component' can now be created where each common~symptom, or lone test case is a failure~mode of this new component
\end{itemize}
@ -291,53 +256,7 @@ thus
The failure modes of the components can be represented as contours on
on the diagram in \ref{fig:gensubsys1}.
\begin{figure}
\centering
\includegraphics[width=3in,height=3in,bb=0 0 513 541]{symptom_abstraction/synmptom_abstraction.jpg}
% synmptom_abstraction.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541
\label{fig:gensubsys1}
\caption{$FG_{cfm}$ Component Failure modes represented as contours}
\end{figure}
% % DIAGRAM WITH SPIDER
% \begin{figure}
% \centering
% \includegraphics[scale=20]{./synmptom_abstraction.jpg}
% % synmptom_abstraction.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541
% \label{fig:gensubsys2}
% \caption{$SS_{cfm}$ Component Failure modes represented as contours}
% \end{figure}
We can now look at the effects that component failure modes have
on the sub-system.
This process involves examining `test cases'. Each `test case' represents the fault behaviour
of the sub-system due to particular combinations of component fault modes.
Each test case can be represented on the diagram as a labeled point.
The labeled point will reside in a region on the diagram
enclosed by the contours representing particular component fault modes.
The label will indicate the fault symptom from the perspective of the sub-system.
For the sake of example, only single component failure modes are considered.
We can now assign a test~case to each contour, and mark it on the diagram.
% \begin{figure}[h+]
% \centering
% \includegraphics[scale=20]{./symptom_abstraction2.jpg}
% % synmptom_abstraction.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541
% \label{fig:gensubsys2}
% \caption{Component Failure modes with analysed test cases}
% \end{figure}
\begin{figure}
\centering
\includegraphics[width=3in,height=3in,bb=0 0 513 541]{symptom_abstraction/symptom_abstraction2.jpg}
% symptom_abstraction2.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541
\label{fig:gensubsys2}
\caption{Component Failure modes with analysed test cases}
\end{figure}
% The failure modes of the components can be represented as contours on on the diagram in \ref{fig:gensubsys1}. \begin{figure} \centering \includegraphics[width=3in,height=3in,bb=0 0 513 541]{symptom_abstraction/synmptom_abstraction.jpg} % synmptom_abstraction.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541 \label{fig:gensubsys1} \caption{$FG_{cfm}$ Component Failure modes represented as contours} \end{figure} % % DIAGRAM WITH SPIDER % \begin{figure} % \centering % \includegraphics[scale=20]{./synmptom_abstraction.jpg} % % synmptom_abstraction.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541 % \label{fig:gensubsys2} % \caption{$SS_{cfm}$ Component Failure modes represented as contours} % \end{figure} We can now look at the effects that component failure modes have on the sub-system. This process involves examining `test cases'. Each `test case' represents the fault behaviour of the sub-system due to particular combinations of component fault modes. Each test case can be represented on the diagram as a labeled point. The labeled point will reside in a region on the diagram enclosed by the contours representing particular component fault modes. The label will indicate the fault symptom from the perspective of the sub-system. For the sake of example, only single component failure modes are considered. We can now assign a test~case to each contour, and mark it on the diagram. % \begin{figure}[h+] % \centering % \includegraphics[scale=20]{./symptom_abstraction2.jpg} % % synmptom_abstraction.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541 % \label{fig:gensubsys2} % \caption{Component Failure modes with analysed test cases} % \end{figure} \begin{figure} \centering \includegraphics[width=3in,height=3in,bb=0 0 513 541]{symptom_abstraction/symptom_abstraction2.jpg} % symptom_abstraction2.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541 \label{fig:gensubsys2} \caption{Component Failure modes with analysed test cases} \end{figure}
\par
\vspace{0.3cm}
@ -355,49 +274,26 @@ $c\_2$ & $fs\_7$ \\ \hline
\vspace{0.3cm}
The sub-system fault symptoms are now represented on the diagram as in figure \ref{fig:gensubsys2}.
A second stage of analysis is now applied.
Empirically, it is often noticed that a sub-system will fail in the same way due to a variety of reasons.
To the `user' of the sub-system, it does not matter which component or combination of components has failed.
The sub-system can thus be considered to have its own set of failure modes.
This stage of the analysis is to determine these, to collect `like symptoms'.
This is performed on the diagram by linking the test cases with lines to form `spiders'
% The sub-system fault symptoms are now represented on the diagram as in figure \ref{fig:gensubsys2}. A second stage of analysis is now applied. Empirically, it is often noticed that a sub-system will fail in the same way due to a variety of reasons. To the `user' of the sub-system, it does not matter which component or combination of components has failed. The sub-system can thus be considered to have its own set of failure modes. This stage of the analysis is to determine these, to collect `like symptoms'. This is performed on the diagram by linking the test cases with lines to form `spiders'
For the sake of example let us consider the fault symptoms $SP1 = \{fs_2, fs_4, fs_5\}$ to be an identical
failure mode at the {\em sub-system} level. These can then be joined to form a spider. Likewise
let $SP2 = \{fs_1, fs_3, fs_7\}$ be an identical failure mode at the {\em sub-system} level.
Let $\{fs_6\}$ be a distinct failure mode at {\em sub-system} level.
The diagram can now be drawn as in figure \ref{fig:gensubsys3}.
% The diagram can now be drawn as in figure \ref{fig:gensubsys3}. % \begin{figure}[h+] % \centering % \includegraphics[scale=20]{./symptom_abstraction3.jpg} % % synmptom_abstraction.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541 % \label{fig:gensubsys3} % \caption{Common failure modes collected as `Spiders'} % \end{figure} \begin{figure}[h+] \centering \includegraphics[width=3in,height=3in,bb=0 0 513 541]{symptom_abstraction/symptom_abstraction3.jpg} % symptom_abstraction3.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541 \label{fig:gensubsys3} \caption{Common failure modes collected as `Spiders'} \end{figure}
% \begin{figure}[h+]
% \centering
% \includegraphics[scale=20]{./symptom_abstraction3.jpg}
% % synmptom_abstraction.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541
% \label{fig:gensubsys3}
% \caption{Common failure modes collected as `Spiders'}
% \end{figure}
\begin{figure}[h+]
\centering
\includegraphics[width=3in,height=3in,bb=0 0 513 541]{symptom_abstraction/symptom_abstraction3.jpg}
% symptom_abstraction3.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541
\label{fig:gensubsys3}
\caption{Common failure modes collected as `Spiders'}
\end{figure}
We have now in $SP1$, $SP2$ and $fs_6$ the three ways in which this sub-system can fail.
In other words we have derived failure modes for this sub-system.
The third stage of the process could be applied automatically.
Each common symptom becomes a failure mode of
a newly created derived component.
The third stage of the process can be applied automatically.
Each `spider' or `lone test case' becomes a contour
in the new diagram (see figure \ref{fig:gensubsys4}.
The result of this will be, a set of failure modes for the sub-system, as though it were a {\em black box}
or a {\em component} to be used in higher level designs.
We have now in $SP1$, $SP2$ and $fs_6$ the three ways in which this sub-system can fail.
In other words we have derived failure modes for this sub-system.
%\section{The Process : To analyse a base level sub-system}
@ -442,7 +338,7 @@ In other words we have derived failure modes for this sub-system.
% is represented as a contour. These contours represent the failure modes of the sub-system.
% \end{itemize}
This sub-system may now therfore, be represented as three separate failure modes.
This sub-system or derived~component may now therefore, be represented as three separate failure modes.
We may now treat this sub-system as we would a component with a known set of failure modes.
The failure modes of the Sub-system $SS$ are now the set $SS_{fm} = \{ SP1, Sp2, fs_6 \}$.
@ -466,23 +362,9 @@ The derivation of $SS_{fm}$ is represented graphically using the `$\bowtie$' sym
% % synmptom_abstraction.jpg: 570x601 pixel, 80dpi, 18.10x19.08 cm, bb=0 0 513 541
% \label{fig:gensubsys3}
% \caption{Deriving a new diagram}
% \end{figure}
%
\begin{figure}[h+]
\centering
\includegraphics[width=3in,height=3in,bb=0 0 376 410]{symptom_abstraction/symptom_abstraction4.jpg}
% symptom_abstraction4.jpg: 418x455 pixel, 80dpi, 13.27x14.45 cm, bb=0 0 376 410
\caption{Deriving a new diagram}
\label{fig:gensubsys4}
\end{figure}
The derived diagram in figure \ref{fig:gensubsys4} shows the functional group of components $A,B,C$
analysed as a sub-system. The result is a set of fault modes that define the fault mode behaviour of that sub-system.
This sub-system, with its three error modes, can now be treated as a component (although at a higher level of abstraction)
This sub-system or derived~component, with its three error modes, can now be treated as a component (although at a higher level of abstraction)
with known failure modes.