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Edits on a Sunday afternoon

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Robin 2010-04-11 14:52:50 +01:00
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17
component_failure_modes_definition/component_failure_modes_definition.tex
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@ -80,6 +80,21 @@ the failure mode set is not unitary~state and does not exist in the family of se
\subsection{Component Failure Modes and Statistical Sample Space}
A sample space is defined as the set of all possible outcomes.
When dealing with failure modes, we are not interested in
the state where the compoent is working perfectly or `OK' (i.e. operating with no error).
We are interested only in ways in which it can fail.
By definition while all components in a system are `working perfectly'
that system will not exhibit faulty behavuiour.
Thus the statistical sample space $\Omega$ for a component/sub-system K is
%$$ \Omega = {OK, failure\_mode_{1},failure\_mode_{2},failure\_mode_{3} ... failure\_mode_{N} $$
$$ \Omega(K) = \{OK, failure\_mode_{1},failure\_mode_{2},failure\_mode_{3} ... failure\_mode_{N}\} $$
The failure mode set for a given component or sub-system $F$
is therefore
$$ F = \Omega(K) \backslash OK $$
\subsection{Bayes Theorem} \subsection{Bayes Theorem}
Describe application - likely hood of faults being the cause of symptoms - Describe application - likely hood of faults being the cause of symptoms -
@ -97,8 +112,6 @@ to
%Thus if the failure~modes are pairwaise mutually exclusive they qualify for inclusion into the %Thus if the failure~modes are pairwaise mutually exclusive they qualify for inclusion into the
%unitary~state set family. %unitary~state set family.
\subsection{Tests of Hypotheses and Significance} \subsection{Tests of Hypotheses and Significance}
In high reliability systems the fauls are often logged - strange occurances - In high reliability systems the fauls are often logged - strange occurances -

28
symptom_abstraction/symptom_abstraction.tex
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@ -21,7 +21,7 @@ of a system can be built.
%FMMD hierarchy %FMMD hierarchy
The hierarchy is built from the bottom up. The hierarchy is built from the bottom up.
Starting with component failure modes at the bottom. Starting with component failure modes at the bottom.
Because the process is bottom-up Because the process is bottom-up, syntax checking and tracking can ensure that
no component failure mode can be overlooked. no component failure mode can be overlooked.
Once a hierarchy is in place it can be converted into a fault data model. Once a hierarchy is in place it can be converted into a fault data model.
@ -38,6 +38,24 @@ This paper focuses on the process of building the blocks that are used in the hi
\section{Introduction} \section{Introduction}
Fault finding is intinctively performed from the top-down.
A faulty peice of equipement is examined and will have a
symptom or specific fault. The area or sub-system within the
equipemnt will next be looked into. Secific measurements
and checks will be made, and finally a component or a low level sub-system
will be found to be faulty.
The technique here works the other way. It works from the bottom up.
Starting with a collection of compoents that form
a simple functional group, the effect of all component error modes are
examined, as to their effect on the functional group.
The effects on the functional group can then be collected as common symptoms,
and now we may treat the functional group as a component. It has a known set of failure modes.
By working from the bottom up, we can trace all possible sources
that could cause a particular mode of equipment failure.
This means that we can obtainm statistical estimates based on the known reliabilities
of the components.
It also means that every component failure mode must at the very least be considered.
\subsection{Static Analysis} \subsection{Static Analysis}
In the field of safety critical engineering; to comply with In the field of safety critical engineering; to comply with
@ -74,9 +92,9 @@ For instance a stereo amplifier separate is a sub-system. The
whole Sound System, consists perhaps of the following `sub-systems': whole Sound System, consists perhaps of the following `sub-systems':
CD-player, tuner, amplifier~separate, loudspeakers and ipod~interface. CD-player, tuner, amplifier~separate, loudspeakers and ipod~interface.
Thinking like this is a top~down analysis approach %Thinking like this is a top~down analysis approach
and is the way in which FTA\cite{nucfta} analyses a System %and is the way in which FTA\cite{nucfta} analyses a System
and breaks it down. %and breaks it down.
A sub-system will be composed of component parts, which A sub-system will be composed of component parts, which
may themselves be sub-systems. However each `component part' may themselves be sub-systems. However each `component part'
@ -107,7 +125,7 @@ for the smallest `functional~groups' of components within a system. A functional
to perform a specific function. to perform a specific function.
When we have analysed the fault behaviour of a functional group, we can treat it as a `black box'. When we have analysed the fault behaviour of a functional group, we can treat it as a `black box'.
We can now call our functional~group a sub-system. We know how will behave under fault conditions ! We can now call our functional~group a sub-system. The goal here is to know how will behave under fault conditions !
%Imagine buying one such `sub~system' from a very honest vendor. %Imagine buying one such `sub~system' from a very honest vendor.
%One of those sir, yes but be warned it may fail in these distinct ways, here %One of those sir, yes but be warned it may fail in these distinct ways, here
%in the honest data sheet the set of failure modes is listed! %in the honest data sheet the set of failure modes is listed!