101 lines
4.0 KiB
TeX
101 lines
4.0 KiB
TeX
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% Make the revision and doc number macro's then they are defined in one place
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\ifthenelse {\boolean{paper}}
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{
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\begin{abstract}
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A survey of Static Failure Mode analysis Methodologies applicable to saefty critical systems.
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\end{abstract}
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}
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{
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\section{Overvew}
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A survey of Static Failure Mode analysis Methodologies applicable to saefty critical systems.
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}
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\section{FMEA}
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Two meanings, a general one Fault Mode Effects Analysis, meaning general statics diagnosis of a design, looking
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at faults that can occur and their effect.
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\subsection{Manufacturing Cost Reduction FMEA}
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Second a methodology for reducing cost in manufacturing by taking fauls, their frequency
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and their cost, multiplying these together, and then coming up with a priority list
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for fixing knmown faults.
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"The basics of FMEA by Robin E. McDermott et all"
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ISBN 0-527-76320-9.
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\subsection{Deterministic FMEA}
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EN298 no two individual component failures may give rise to a dangerous condition.
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\section{FMEDA Failure effect Mode Diagnositic Analysis}
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This is the main babsis of SIL certification for Programmed Electronic Equipment.
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Itr applies FMEA, with classification of criticality of
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components, adjustment to MTTF values by self checking mechanisms in the product,
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and mitigation for a safe failure fraction. This leads to a probablistic
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mean time to failure or probability of failure on demand, that will
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fall within the criteria for a given SIL safety level.
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An overview for this method can be found in an EXIDA paper \cite{fmeda}
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and detailed description of the method for SIL certification in part 2 of
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EN61508 \cite{en61508}.
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disadvantage: single component failure is used to determine its effect on
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the entire system. This leads to classifying components as safety or non-safety critical
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at an early stage in the analysis. This means that complex interactions or side effects
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of the components failing may not be taken into account.
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advantage: concepts of self checking systems, and safe failure fraction\footnote{Safe Failure Fraction (SFF) is the number of non-safety critical components
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that can be detected as failed compared to the number of safety critcal components. The thinking here is that is components are detected as failing
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even though they are not safety critical, the system is self checking a greater proportion of its own systems, and is therefore safer. This
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is applying bayes theorem for probablistic error detection}
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This is a probablistic based methodology.
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\subsection{Safe Failure Fraction}
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Introduce the idea of coverage.
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A good example is RAM in a microprocessor/microcontroller, we cann ot give 100i\% coverage to it.
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We can perform some tests that give us 60\% coverage etc
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\subsection{Diagnostic interval}
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Reducing FIT with detecting a fraction of the faults within an interval. Give formulas etc
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\subsection{Redundancy - Models}
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1oo1 2oo3 etc
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\subsection{Field Data}
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OK for EN61508, not OK for nuclear industry find refs.
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\section {FTA}
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Fault tree Analysis
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Show how it works, top down,
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FROM INTERBET HISTORY OF FTA
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%%- RE_PHRASE %%
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%%- RE_PHRASE %% Fault tree analysis (FTA) is a tool originally developed in
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%% RE_PHRASE %% 1962 by Bell Labs for use in studying failure modes in the
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%% RE_PHRASE %% launch control system of the Minuteman missile project. The tool now
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%% RE_PHRASE %% finds wide use in numerous applications, from accident investigation to design
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%% RE_PHRASE %% prototyping, and is also finding use for protection and control related
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%% RE_PHRASE %% applications. This paper provides an elementary background to the application of
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%% RE_PHRASE %% FTA for use in protection applications. The construction of the fault
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%% RE_PHRASE %% tree as well as the use of reliability data is considered.
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%% RE_PHRASE %% A simple example is presented. The intention is to provide a
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%% RE_PHRASE %% brief introduction to the concept, to allow users to at least
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%% RE_PHRASE %% understand how a fault tree is constructed and what can be done
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%% RE_PHRASE %% with it.
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% read exita doc and ref it
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% typeset in {\Huge \LaTeX} \today
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