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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
% 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
working heuristically. A base component failure will typically
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
event are completely determined, a large amount of work not
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.
% take a circuit or system and follow all the interactions
% 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{Defining the concept of `comparison~complexity' in FMEA}
\label{sec:cc}
%
% DOMAIN == INPUTS
% 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.
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.
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
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!).
%
Obviously, for a small number of components and failure modes, we have a smaller number