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Robin Clark 2012-05-12 11:14:48 +01:00
parent be339784b7
commit e1461615d7
2 changed files with 11 additions and 3 deletions
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8
submission_thesis/CH4_FMMD/copy.tex
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@ -170,7 +170,8 @@ To look in detail at half a million fault~scenarios is obviously impractical.
% Requirements for an improved methodology The deficiencies identified in the % Requirements for an improved methodology The deficiencies identified in the
% current methodologies are used to establish criteria for an improved methodology. % current methodologies are used to establish criteria for an improved methodology.
\paragraph{Reasoning distance - complexity and reach-ability.} \paragraph{Reasoning distance - complexity and reachability.}
\label{sec:rd}
Tracing a component level failure up to a top level event, without the rigour accompanying state explosion, involves Tracing a component level failure up to a top level event, without the rigour accompanying state explosion, involves
working heuristically. A base component failure will typically working heuristically. A base component failure will typically
be conceptually removed by several stages from a top level event. be conceptually removed by several stages from a top level event.
@ -192,6 +193,11 @@ from the base component failure to the system level event.
The reasoning distance serves to show that when the causes of a top level The reasoning distance serves to show that when the causes of a top level
event are completely determined, a large amount of work not event are completely determined, a large amount of work not
typical of heuristic or intuitive interpretation is required. typical of heuristic or intuitive interpretation is required.
Reasoning distances will be large for complicated systems, and this is therefore a weakness in both
FMEA and FTA type analyses. This concept is developed further to create a metric for comparing
complexities from FMEA and FMMD analysis in section~\ref{sec:cc}.
% could have a chapter on this. % could have a chapter on this.
% take a circuit or system and follow all the interactions % take a circuit or system and follow all the interactions
% to the components that cause the system level event. % to the components that cause the system level event.

6
submission_thesis/CH6_Evaluation/copy.tex
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@ -1,7 +1,7 @@
\section*{Metrics} \section*{Metrics}
\section{Defining the concept of `comparison~complexity' in FMEA} \section{Defining the concept of `comparison~complexity' in FMEA}
\label{sec:cc}
% %
% DOMAIN == INPUTS % DOMAIN == INPUTS
% RANGE == OUTPUTS % RANGE == OUTPUTS
@ -17,11 +17,13 @@ we could stipulate that every failure mode must be checked for effects
against all the components in the system. against all the components in the system.
We could term this `rigorous~FMEA'~(RFMEA). We could term this `rigorous~FMEA'~(RFMEA).
The number of checks we have to make to achieve this, gives an indication of the complexity of the task. The number of checks we have to make to achieve this, gives an indication of the complexity of the task.
This is described in section~\ref{sec:rd}, where the reasoning distance, or complexity to
analyse a single FMEA failure scenario, is given in equation \ref~{eqn:complexity}.
% %
We could term this `comparison~complexity', as the number of We could term this `comparison~complexity', as the number of
paths between failure modes and components necessary to achieve RFMEA for a given system/functional~group. paths between failure modes and components necessary to achieve RFMEA for a given system/functional~group.
% (except its self of course, that component is already considered to be in a failed state!). % (except its self of course, that component is already considered to be in a failed state!).
% %
Obviously, for a small number of components and failure modes, we have a smaller number Obviously, for a small number of components and failure modes, we have a smaller number