OK still need to:
Go through Chris Garret CH6 note First half CH7 notes, and remove allot of formal defs from CH7
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@ -223,6 +223,12 @@ i.e.
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\label{ros}
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\label{ros}
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$$ fm(R) = \{ OPEN, SHORT \} . $$
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$$ fm(R) = \{ OPEN, SHORT \} . $$
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%
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% Mention tolerance here
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%
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% hmmmmmm
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%
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\subsection{Failure modes determination for generic operational amplifier}
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\subsection{Failure modes determination for generic operational amplifier}
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\begin{figure}[h+]
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\begin{figure}[h+]
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@ -387,6 +393,10 @@ The EN298 pinouts failure mode technique cannot reveal failure modes due to inte
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The FMD-91 entries for op-amps are not directly usable as
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The FMD-91 entries for op-amps are not directly usable as
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component {\fms} in FMEA or FMMD and require interpretation.
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component {\fms} in FMEA or FMMD and require interpretation.
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%For our OpAmp example could have come up with different symptoms for both sides. Cannot predict the effect of internal errors, for instance ($LOW_{slew}$)
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%For our OpAmp example could have come up with different symptoms for both sides. Cannot predict the effect of internal errors, for instance ($LOW_{slew}$)
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%is missing from the EN298 failure modes set.
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%is missing from the EN298 failure modes set.
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@ -569,12 +579,21 @@ get a balance between subjective and objective perspectives.
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%for the the results of an FMEA line of reasoning.
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%for the the results of an FMEA line of reasoning.
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\paragraph{Failure modes, observability criterion: detectable and undetectable.}
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\paragraph{Failure modes and their observability criterion: detectable and undetectable.}
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Often the effects of a failure mode may be easy to detect, and our equipment can react by raising an alarm or compensating for the resulting fault.
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Often the effects of a failure mode may be easy to detect,
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Some failure modes may cause undetectable failure, for instance a component that causes
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and our equipment can react by raising an alarm or compensating for the resulting fault.
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a measured reading to change could have dire consequences yet not be obvious.
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%
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In fault diagnosis failures are said to be observable and unobservable~\cite{721666, ACS:ACS1297}.
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Some failure modes may cause undetectable failures, for instance a component that causes
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\glossary{name={observability}, description={The property of a system failure in relation to a particular component failure mode, where it can bedetermined whether the readings/actions associated with it are valid, or the by-product of a failure. If we cannot determine that there is a fault present, the system level failure is said to be unobservable.}}
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a measured reading to change could have adverse consequences yet not be flagged as a failure.
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This type of failure would not be flagged as a failure by the system, because
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it has no way of knowing the reading is invalid.
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%
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The term observable has a specific meaning in the field of control engineering~\cite{721666, ACS:ACS1297};
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systems submitted for FMEA are generally related to control systems,
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and so to avoid confusion the terms `detectable' and `undetectable'
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will be used for describing the observability of failure modes in this document.
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\glossary{name={observability}, description={The property of a system failure in relation to a particular component failure mode, where it can be determined whether the readings/actions associated with it are valid, or the by-product of a failure. If we cannot determine that there is a fault present, the system level failure is said to be unobservable.}}
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\paragraph{Impracticality of Field Data for modern systems.}
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\paragraph{Impracticality of Field Data for modern systems.}
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@ -629,12 +648,12 @@ would give a reasoning distance of 3 * 100 * 99.
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%{sfmeaforwardbackward}
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%{sfmeaforwardbackward}
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\subsection{FMEA and the State Explosion Problem}
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\subsection{FMEA and the State Explosion Problem}
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\paragraph{Rigorous Single Failure FMEA.}
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\paragraph{Exhaustive Single Failure FMEA.}
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FMEA for a safety critical certification~\cite{en298,en61508} will have to be applied
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FMEA for a safety critical certification~\cite{en298,en61508} will have to be applied
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to all known failure modes of all components within a system.
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to all known failure modes of all components within a system.
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To perform FMEA rigorously (i.e. to examine every possible interaction
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To perform FMEA exhaustively (i.e. to examine every possible interaction
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of a failure mode with all other components in a system). Or in other words,
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of a failure mode with all other components in a system). Or in other words,
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---we would need to look at all possible failure scenarios.
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---we would need to look at all possible failure scenarios.
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%to do this completely (all failure modes against all components).
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%to do this completely (all failure modes against all components).
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@ -650,13 +669,13 @@ $f$ is the number of failure modes per component.
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\end{equation}
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\end{equation}
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\paragraph{Rigorous Single Failure FMEA}
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\paragraph{Exhaustive Single Failure FMEA}
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This would mean an order of $O(N^2)$ number of checks to perform
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This would mean an order of $O(N^2)$ number of checks to perform
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to undertake a `rigorous~FMEA'. Even small systems have typically
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to undertake an `exhaustive~FMEA'. Even small systems have typically
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100 components, and they typically have 3 or more failure modes each.
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100 components, and they typically have 3 or more failure modes each.
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$100*99*3=29,700$.
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$100*99*3=29,700$.
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\paragraph{Rigorous Double Failure FMEA}
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\paragraph{Exhaustive Double Failure FMEA}
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For looking at potential double failure
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For looking at potential double failure
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scenarios\footnote{Certain double failure scenarios are already legal requirements---The European Gas burner standard (EN298:2003)---demands the checking of
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scenarios\footnote{Certain double failure scenarios are already legal requirements---The European Gas burner standard (EN298:2003)---demands the checking of
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double failure scenarios (for burner lock-out scenarios).}
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double failure scenarios (for burner lock-out scenarios).}
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@ -673,19 +692,25 @@ $100*99*98*3=2,910,600$ failure mode scenarios.
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\paragraph{Reliance of experts for meaningful FMEA Analysis.}
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\paragraph{Reliance of experts for meaningful FMEA Analysis.}
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Current FMEA methodologies cannot consider---for practical reasons---a rigorous approach.
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Current FMEA methodologies cannot consider---for the reason of state explosion---an exhaustive approach.
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We define rigorous FMEA as examining the effect of every component failure mode
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We define exhaustive FMEA ({\XFMEA}) as examining the effect of every component failure mode
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against the remaining components in the system under investigation.
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against the remaining components in the system under investigation.
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%
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%
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Because we cannot perform rigorous FMEA,
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Because we cannot perform XFMEA,
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we rely on experts in the system under investigation
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we rely on experts in the system under investigation
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to perform a meaningful FMEA analysis.
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to perform a meaningful FMEA analysis.
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%
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%
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In practise these experts have to select the areas they see as most critical for detailed FMEA analysis.
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In practise these experts have to select the areas they see as most critical for detailed FMEA analysis.
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\subsection{Component Tolerance}
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Component tolerances may need considered when determining if a component has failed.
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Calculations for acceptable ranges to determine failure or acceptable conditions
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must be made where appropriate.
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An example of component tolerance considered for FMEA
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is given in section~\ref{sec:resistortolerance}.
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\section{FMEA in practise: Five variants}
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\section{FMEA in current usage: Five variants}
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\paragraph{Five main Variants of FMEA}
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\paragraph{Five main Variants of FMEA}
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\begin{itemize}
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\begin{itemize}
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@ -35,15 +35,28 @@ This problem is compounded by the fact that traditional FMEA cannot integrate so
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Traditional FMEA cannot ensure that each failure mode of all its
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Traditional FMEA cannot ensure that each failure mode of all its
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components are checked against any other components in the system which
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components are checked against any other components in the system which
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it may affect, due to state explosion.
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it may affect, due to state explosion.
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%
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FMEA is therefore performed using heuristics to decide
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FMEA is therefore performed using heuristics to decide
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which components to check the effect of a component failure mode on.
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which components to check the effect of a component failure mode on.
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We could term the number of checks made for each failure mode
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We could term the number of checks made for each failure mode
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on aspects of the system to be the reasoning distance.
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on aspects of the system to be the reasoning distance.
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%
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In practise FMEA may be performed by following the signal path
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of the component failure mode to its system level effect. This is less than ideal
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and it can easily miss interactions with adjacent components, that could cause
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other system level symptoms.
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%
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Were we to compare the reasoning distance with the theoretical maximum, the sum of all failure
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Were we to compare the reasoning distance with the theoretical maximum, the sum of all failure
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modes in a system, multiplied by the number of components in it, we could arrive at a comparison complexity figure.
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modes in a system, multiplied by the number of components in it, we could arrive at a comparison complexity figure.
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This figure would mean we could compare the maximum number of checks (i.e. rigorous analysis)
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This figure would mean we could compare the maximum number of checks (i.e. exhaustive%rigorous
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with the number actually performed.
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analysis) with the number actually performed.
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\paragraph{The ideal of exhaustive FMEA (XFMEA)}
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Obviously, exhaustively checking every component failure mode in a system,
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against all other components is the ideal for finding all possible system level failures.
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While this is impossible for all but trivial systems, it should be possible
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for small groups of components that work together to provide a well defined function.
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We could term such a group a `{\fg}'.
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\section{Re-use of FMEA analysis}
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\section{Re-use of FMEA analysis}
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@ -136,7 +149,8 @@ of the communications protocol used to transmit data, and the failure mode chara
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of the communications physical layer.
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of the communications physical layer.
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%(figure~\ref{fig:distcon}
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%(figure~\ref{fig:distcon}
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The failure reasoning paths for a distributed real time system, mean traditional FMEA
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The failure reasoning paths for a distributed real time system, with its multiple passes of the hardware/software
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interface mean traditional FMEA, for these systems,
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is impossible to perform.
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is impossible to perform.
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%
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%
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The base component failure mode to system failure paradigm is
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The base component failure mode to system failure paradigm is
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@ -163,11 +177,11 @@ utterly anachronistic in the distributed real time system environment.
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\begin{itemize}
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\begin{itemize}
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\item FMEA type methodologies were designed for simple electro-mechanical systems of the 1940's to 1960's.
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\item FMEA type methodologies were designed for simple electro-mechanical systems of the 1940's to 1960's.
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\item Reasoning Distance - component failure to system level symptom
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\item Reasoning Distance - component failure to system level symptom
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\item State explosion - impossible to perform rigorously
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\item State explosion - impossible to perform FMEA exhaustively %rigorously
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\item Difficult to re-use previous analysis work
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\item Difficult to re-use previous analysis work
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\item Very Difficult to model simultaneous failures.
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\item Very Difficult to model simultaneous failures.
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\item Software and hardware models are separate.
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\item Software and hardware models are separate.
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\item Distributed real time systemsare very difficult to meaningfully analyse with FMEA.
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\item Distributed real time systems are very difficult to meaningfully analyse with FMEA.
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\end{itemize}
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\end{itemize}
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FMEA is no longer fit for purpose!
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FMEA is no longer fit for purpose!
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@ -2207,9 +2207,9 @@ Ensuring this condition is described in section~\ref{sec:completetest}.
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\paragraph{State explosion problem of FMEA solved by FMMD.}
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\paragraph{State explosion problem of FMEA solved by FMMD.}
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%
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%
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Because FMMD considers failure modes within functional groups;
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Because FMMD considers failure modes within functional groups;
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the traditional state explosion problem in FMEA where each failure
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the traditional state explosion problem in FMEA where the ideal of exhaustive FMEA (XFMEA)---where each failure
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mode could be considered in the context of all other components in the system
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mode could be considered in the context of all other components in the system---disappears.
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disappears.
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FMMD applies XFMEA within {\fgs}.
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%
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%
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This issue addressed formally in section~\ref{sec:cc}.
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This issue addressed formally in section~\ref{sec:cc}.
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@ -2073,28 +2073,29 @@ Temperature range calculations and detailed calculations
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on the effects of each test case are found in section \ref{Pt100range}
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on the effects of each test case are found in section \ref{Pt100range}
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and \ref{Pt100temp}.
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and \ref{Pt100temp}.
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%\paragraph{Consideration of Resistor Tolerance}
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\paragraph{Consideration of Resistor Tolerance}
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%
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\label{sec:resistortolerance}
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%The separate sense lines ensure the voltage read over the Pt100 thermistor are not
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The separate sense lines ensure the voltage read over the Pt100 thermistor are not
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%altered due to having to pass any significant current.
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altered due to having to pass any significant current.
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%The Pt100 element is a precision part and will be chosen for a specified accuracy/tolerance range.
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The Pt100 element is a precision part and will be chosen for a specified accuracy/tolerance range.
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%One or other of the load resistors (the one we measure current over) should also
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One or other of the load resistors (the one we measure current over) should also
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%be of this accuracy.
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be of this accuracy.
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%
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%The \ohms{2k2} loading resistors may be ordinary, in that they would have a good temperature co-effecient
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The \ohms{2k2} loading resistors may be ordinary, in that they would have a good temperature co-effecient
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%(typically $\leq \; 50(ppm)\Delta R \propto \Delta \oc $), and should be subjected to
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(typically $\leq \; 50(ppm)\Delta R \propto \Delta \oc $), and should be subjected to
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%a narrow temperature range anyway, being mounted on a PCB.
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a narrow temperature range anyway, being mounted on a PCB.
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%\glossary{{PCB}{Printed Circuit Board}}
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%\glossary{{PCB}{Printed Circuit Board}}
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%To calculate the resistance of the Pt100 element % (and thus derive its temperature),
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To calculate the resistance of the Pt100 element % (and thus derive its temperature),
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%having the voltage over it, we now need the current.
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having the voltage over it, we now need the current.
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%Lets use, for the sake of example $R_2$ to measure the current flowing in the temperature sensor loop.
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Lets use, for the sake of example $R_2$ to measure the current flowing in the temperature sensor loop.
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%As the voltage over $R_3$ is relative (a design feature to eliminate resistance effects of the cables).
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As the voltage over $R_3$ is relative (a design feature to eliminate resistance effects of the cables).
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%We can calculate the current by reading
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We can calculate the current by reading
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%the voltage over the known resistor $R2$.\footnote{To calculate the resistance of the Pt100 we need the current flowing though it.
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the voltage over the known resistor $R2$.\footnote{To calculate the resistance of the Pt100 we need the current flowing though it.
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%We can determine this via ohms law applied to $R_2$, $V=IR$, $I=\frac{V}{R_2}$,
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We can determine this via ohms law applied to $R_2$, $V=IR$, $I=\frac{V}{R_2}$,
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%and then using $I$, we can calculate $R_{3} = \frac{V_{R3}}{I}$.}
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and then using $I$, we can calculate $R_{3} = \frac{V_{R3}}{I}$.}
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%As these calculations are performed by ohms law, which is linear, the accuracy of the reading
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As these calculations are performed by ohms law, which is linear, the accuracy of the reading
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%will be determined by the accuracy of $R_2$ and $R_{3}$. It is reasonable to
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will be determined by the accuracy of $R_2$ and $R_{3}$.
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%It is reasonable to
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%take the mean square error of these accuracy figures.
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%take the mean square error of these accuracy figures.
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\paragraph{Range and $Pt100$ Calculations}
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\paragraph{Range and $Pt100$ Calculations}
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@ -15,7 +15,7 @@ complexity of applying FMEA to a group of components.
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%
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%
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These formulae are then used for a hypothetical example, which is analysed by both FMEA and FMMD.
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These formulae are then used for a hypothetical example, which is analysed by both FMEA and FMMD.
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After analysing hypothetical examples, the FMMD examples from chapter~\ref{sec:chap5} are
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After analysing hypothetical examples, the FMMD examples from chapter~\ref{sec:chap5} are
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compared against RFMEA.
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compared against {\XFMEA}.
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%
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%
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Following on from the formal definitions, `unitary state failure modes' are defined. In short these
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Following on from the formal definitions, `unitary state failure modes' are defined. In short these
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ensure that component failure modes are mutually exclusive. % Using the unitary state failure mode definition
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ensure that component failure modes are mutually exclusive. % Using the unitary state failure mode definition
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@ -93,14 +93,14 @@ side effects of failure may manifest due interaction with other components not o
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The temptation with FMEA can be to follow direct lines of failure effect reasoning without considering
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The temptation with FMEA can be to follow direct lines of failure effect reasoning without considering
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side effects.
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side effects.
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%%
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%%
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To perform FMEA rigorously
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To perform FMEA exhaustively % rigorously
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we could stipulate that every failure mode must be checked for effects
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we could stipulate that every failure mode must be checked for effects
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against all the components in the system.
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against all the components in the system.
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%
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%
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This would mean we would be %looking
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This would mean we would be %looking
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examining for all possible side effects that a base component failure could cause.
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examining for all possible side effects that a base component failure could cause.
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%
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%
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We could term this `rigorous~FMEA'~(RFMEA).
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We could term this `exhaustive~FMEA'~({\XFMEA}).
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The number of checks we have to make to achieve this, gives an indication of the complexity of the analysis task.
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The number of checks we have to make to achieve this, gives an indication of the complexity of the analysis task.
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%
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%
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%This is described in section~\ref{sec:rd}, where the reasoning distance, or complexity to
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%This is described in section~\ref{sec:rd}, where the reasoning distance, or complexity to
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@ -110,7 +110,7 @@ The number of checks we have to make to achieve this, gives an indication of the
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%It is desirable to be able to measure the complexity of an analysis task.
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%It is desirable to be able to measure the complexity of an analysis task.
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%
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%
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We define comparison~complexity as the count of
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We define comparison~complexity as the count of
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paths between failure modes and components necessary to achieve RFMEA for a given group
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paths between failure modes and components necessary to achieve {\XFMEA} for a given group
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of components $G$. %system or {\fg}.
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of components $G$. %system or {\fg}.
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% (except its self of course, that component is already considered to be in a failed state!).
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% (except its self of course, that component is already considered to be in a failed state!).
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@ -145,11 +145,12 @@ we can represent the number of potential failure modes of a component $c$, to be
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\paragraph{Indexing components with the group $G$.}
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\paragraph{Indexing components with the group $G$.}
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If we index all the components in the system under investigation $ c_1, c_2 \ldots c_{|G|} $ we can express
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If we index all the components in the system under investigation $ c_1, c_2 \ldots c_{|G|} $ we can express
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the number of checks required to rigorously examine every
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the number of checks required to exhaustively % rigorously
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examine every
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failure mode against all the other components in a system.
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failure mode against all the other components in a system.
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%
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%
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Comparison Complexity can be represented by a function $CC$, with its domain as $G$, and
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Comparison Complexity can be represented by a function $CC$, with its domain as $G$, and
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its range as the number of checks---or reasoning stages---to perform to satisfy a rigorous FMEA inspection.
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its range as the number of checks---or reasoning stages---to perform to satisfy an XFMEA inspection.
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Where $\mathcal{G}$ represents the set of all {\fgs} %, and $ \mathbb{Z}^{+} $,
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Where $\mathcal{G}$ represents the set of all {\fgs} %, and $ \mathbb{Z}^{+} $,
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$CC$ is defined by,
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$CC$ is defined by,
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@ -244,7 +245,7 @@ We combine the potential divider with an op-amp which has four failure modes
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to form a {\fg} with two components, one with four failure modes and the other (the potential divider) with two.
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to form a {\fg} with two components, one with four failure modes and the other (the potential divider) with two.
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$$CC(invamp) = 2 \times 1 + 4 \times 1 = 6 $$
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$$CC(invamp) = 2 \times 1 + 4 \times 1 = 6 $$
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To analyse the inverting amplifier with FMMD we required 10 reasoning stages.
|
To analyse the inverting amplifier with FMMD we required 10 reasoning stages.
|
||||||
Using RFMEA we obtain $ 2 \times (3-1) + 2 \times (3-1) + 4 \times (3-1)$ = 16.
|
Using {\XFMEA} we obtain $ 2 \times (3-1) + 2 \times (3-1) + 4 \times (3-1)$ = 16.
|
||||||
|
|
||||||
\paragraph{Complexity Comparison for an hypothetical 81 component system.}
|
\paragraph{Complexity Comparison for an hypothetical 81 component system.}
|
||||||
%Even considering a $example$
|
%Even considering a $example$
|
||||||
@ -254,22 +255,24 @@ having 3 failure modes each) we would have an $CC$ of
|
|||||||
$$CC(example) = \sum_{n=1}^{81} |3|.(|80|) = 19440 .$$
|
$$CC(example) = \sum_{n=1}^{81} |3|.(|80|) = 19440 .$$
|
||||||
|
|
||||||
Ensuring all component failure modes are checked against all other components in a system
|
Ensuring all component failure modes are checked against all other components in a system
|
||||||
-- applying FMEA rigorously -- could be termed
|
-- applying FMEA exhaustively
|
||||||
Rigorous FMEA (RFMEA).
|
%rigorously
|
||||||
The computational order for RFMEA would be polynomial ($O(N^2.K)$) (where $K$ is the variable number of failure modes).
|
-- could be termed
|
||||||
|
exhaustive FMEA ({\XFMEA}).
|
||||||
|
The computational order for {\XFMEA} would be polynomial ($O(N^2.K)$) (where $K$ is the variable number of failure modes).
|
||||||
%
|
%
|
||||||
This order may be acceptable in a computational environment. However, the choosing of {\fgs} and the analysis
|
This order may be acceptable in a computational environment. However, the choosing of {\fgs} and the analysis
|
||||||
process are by-hand/human activities. It can be seen that it is practically impossible to achieve
|
process are by-hand/human activities. It can be seen that it is practically impossible to achieve
|
||||||
RFMEA for anything but trivial systems.
|
{\XFMEA} for anything but trivial systems.
|
||||||
%
|
%
|
||||||
% Next statement needs alot of justification
|
% Next statement needs alot of justification
|
||||||
%
|
%
|
||||||
It is the author's belief that FMMD reduces the comparison complexity enough to make
|
It is the author's belief that FMMD reduces the comparison complexity enough to make
|
||||||
rigorous checking feasible.
|
exhaustive checking (within {\fgs}) entirely feasible.
|
||||||
|
|
||||||
|
|
||||||
\pagebreak[4]
|
\pagebreak[4]
|
||||||
%\subsection{Using the concept of Complexity Comparison to compare RFMEA with FMMD}
|
%\subsection{Using the concept of Complexity Comparison to compare {\XFMEA} with FMMD}
|
||||||
|
|
||||||
% \begin{figure}
|
% \begin{figure}
|
||||||
% \centering
|
% \centering
|
||||||
@ -288,16 +291,16 @@ rigorous checking feasible.
|
|||||||
\end{figure}
|
\end{figure}
|
||||||
|
|
||||||
|
|
||||||
\subsection{Comparing FMMD and RFMEA comparison complexity}
|
\subsection{Comparing FMMD and {\XFMEA} comparison complexity}
|
||||||
|
|
||||||
Because components have variable numbers of failure modes,
|
Because components have variable numbers of failure modes,
|
||||||
and {\fgs} have variable numbers of components, it is difficult to
|
and {\fgs} have variable numbers of components, it is difficult to
|
||||||
use the general formula for comparing the number of checks to make for
|
use the general formula for comparing the number of checks to make for
|
||||||
RFMEA and FMMD.
|
{\XFMEA} and FMMD.
|
||||||
%
|
%
|
||||||
If we were to create an example by fixing the number of components in a {\fg}
|
If we were to create an example by fixing the number of components in a {\fg}
|
||||||
and the number of failure modes per component, we can derive formulae
|
and the number of failure modes per component, we can derive formulae
|
||||||
to compare the number of checks to make from an FMMD hierarchy to RFMEA applied to
|
to compare the number of checks to make from an FMMD hierarchy to {\XFMEA} applied to
|
||||||
all components in a system.
|
all components in a system.
|
||||||
|
|
||||||
Consider $k$ to be the number of components in a {\fg} (i.e. $k=|{\FG}|$),
|
Consider $k$ to be the number of components in a {\fg} (i.e. $k=|{\FG}|$),
|
||||||
@ -312,16 +315,16 @@ with equation~\ref{eqn:anscen}.
|
|||||||
\end{equation}
|
\end{equation}
|
||||||
|
|
||||||
The thinking behind equation~\ref{eqn:anscen}, is that for each level of analysis -- counting down from the top --
|
The thinking behind equation~\ref{eqn:anscen}, is that for each level of analysis -- counting down from the top --
|
||||||
there are ${k}^{n}$ {\fgs} within each level; we need to apply RFMEA to each {\fg} on the level.
|
there are ${k}^{n}$ {\fgs} within each level; we need to apply {\XFMEA} to each {\fg} on the level.
|
||||||
%
|
%
|
||||||
The number of checks to make for RFMEA, is the number of components $k$ multiplied by the number of failure modes $f$
|
The number of checks to make for {\XFMEA}, is the number of components $k$ multiplied by the number of failure modes $f$
|
||||||
checked against the remaining components in the {\fg} $(k-1)$.
|
checked against the remaining components in the {\fg} $(k-1)$.
|
||||||
%
|
%
|
||||||
If, for the sake of example, we fix the number of components in a {\fg} to three and
|
If, for the sake of example, we fix the number of components in a {\fg} to three and
|
||||||
the number of failure modes per component to three, an FMMD hierarchy
|
the number of failure modes per component to three, an FMMD hierarchy
|
||||||
would look like figure~\ref{fig:three_tree}.
|
would look like figure~\ref{fig:three_tree}.
|
||||||
|
|
||||||
\subsection{RFMEA FMMD Comparison Example}
|
\subsection{{\XFMEA} FMMD Comparison Example}
|
||||||
|
|
||||||
Using the diagram in figure~\ref{fig:three_tree}, we have three levels of analysis.
|
Using the diagram in figure~\ref{fig:three_tree}, we have three levels of analysis.
|
||||||
%
|
%
|
||||||
@ -334,17 +337,17 @@ On the level below that, we have three {\fgs} each with
|
|||||||
an identical number of checks, $3^1 \times 3 \times 2 \times 3 = 56$. %{\fg}
|
an identical number of checks, $3^1 \times 3 \times 2 \times 3 = 56$. %{\fg}
|
||||||
%
|
%
|
||||||
On the level below that we have nine {\fgs}, $3^2 \times 3\times2\times3=168$.
|
On the level below that we have nine {\fgs}, $3^2 \times 3\times2\times3=168$.
|
||||||
Adding these together gives $242$ checks to make to perform FMMD (i.e. RFMEA {\em{within the}}
|
Adding these together gives $242$ checks to make to perform FMMD (i.e. {\XFMEA} {\em{within the}}
|
||||||
{\fgs}).
|
{\fgs}).
|
||||||
|
|
||||||
If we were to take the system represented in figure~\ref{fig:three_tree}, and
|
If we were to take the system represented in figure~\ref{fig:three_tree}, and
|
||||||
apply RFMEA on it as a whole system, we can use equation~\ref{eqn:CC},
|
apply {\XFMEA} on it as a whole system, we can use equation~\ref{eqn:CC},
|
||||||
$CC(G) = \sum_{n=1}^{|G|} |fm(c_n)|.(|G|-1)$, where $|G|$ is 27, $fm(c_n)$ is 3
|
$CC(G) = \sum_{n=1}^{|G|} |fm(c_n)|.(|G|-1)$, where $|G|$ is 27, $fm(c_n)$ is 3
|
||||||
and $(|G|-1)$ is 26.
|
and $(|G|-1)$ is 26.
|
||||||
This gives:
|
This gives:
|
||||||
$CC(G) = \sum_{n=1}^{27} |3|.(|27|-1) = 2106$.
|
$CC(G) = \sum_{n=1}^{27} |3|.(|27|-1) = 2106$.
|
||||||
|
|
||||||
In order to get general equations with which to compare RFMEA with FMMD,
|
In order to get general equations with which to compare {\XFMEA} with FMMD,
|
||||||
we can re-write equation~\ref{eqn:CC} in terms of the number of levels
|
we can re-write equation~\ref{eqn:CC} in terms of the number of levels
|
||||||
in an FMMD hierarchy.
|
in an FMMD hierarchy.
|
||||||
%
|
%
|
||||||
@ -367,8 +370,8 @@ or
|
|||||||
%(N^2 - N).f
|
%(N^2 - N).f
|
||||||
\end{equation}
|
\end{equation}
|
||||||
|
|
||||||
We can now use equation~\ref{eqn:anscen} (FMMD) and \ref{eqn:CC} (RFMEA) to compare (for fixed sizes of $|G|$ and $|fm(c)|$)
|
We can now use equation~\ref{eqn:anscen} (FMMD) and \ref{eqn:CC} ({\XFMEA}) to compare (for fixed sizes of $|G|$ and $|fm(c)|$)
|
||||||
the two approaches, for the work required to perform rigorous checking.
|
the two approaches, for the work required to perform exhaustive checking.
|
||||||
|
|
||||||
|
|
||||||
For instance, having four levels
|
For instance, having four levels
|
||||||
@ -396,11 +399,11 @@ $$
|
|||||||
|
|
||||||
All the FMMD examples in chapters \ref{sec:chap5}
|
All the FMMD examples in chapters \ref{sec:chap5}
|
||||||
and \ref{sec:chap6} showed a marked reduction in comparison
|
and \ref{sec:chap6} showed a marked reduction in comparison
|
||||||
complexity compared to the RFMEA worst case figures.
|
complexity compared to the {\XFMEA} worst case figures.
|
||||||
To calculate RFMEA comparison complexity equation~\ref{eqn:CC} is used.
|
To calculate {\XFMEA} comparison complexity equation~\ref{eqn:CC} is used.
|
||||||
%
|
%
|
||||||
%
|
%
|
||||||
Complexity comparison vs. RFMEA for the first three examples
|
Complexity comparison vs. {\XFMEA} for the first three examples
|
||||||
are presented in table~\ref{tbl:firstcc}.
|
are presented in table~\ref{tbl:firstcc}.
|
||||||
%
|
%
|
||||||
%\usepackage{multirow}
|
%\usepackage{multirow}
|
||||||
@ -413,7 +416,7 @@ are presented in table~\ref{tbl:firstcc}.
|
|||||||
\textbf{Level} & \textbf{Component} & \textbf{Comparison} & \textbf{of derived} \\
|
\textbf{Level} & \textbf{Component} & \textbf{Comparison} & \textbf{of derived} \\
|
||||||
& & & \textbf{failure modes} \\
|
& & & \textbf{failure modes} \\
|
||||||
%\hline \hline
|
%\hline \hline
|
||||||
%\multicolumn{3}{ |c| }{Complexity Comparison against RFMEA for examples in Chapter~\ref{sec:chap5}} \\
|
%\multicolumn{3}{ |c| }{Complexity Comparison against {\XFMEA} for examples in Chapter~\ref{sec:chap5}} \\
|
||||||
%\hline \hline
|
%\hline \hline
|
||||||
|
|
||||||
|
|
||||||
@ -427,14 +430,14 @@ are presented in table~\ref{tbl:firstcc}.
|
|||||||
0 & PD & 4 & 2 \\
|
0 & PD & 4 & 2 \\
|
||||||
1 & INVAMP & 8 & 3 \\
|
1 & INVAMP & 8 & 3 \\
|
||||||
2 & Total for INVAMP: & 10 (FMMD) & \\
|
2 & Total for INVAMP: & 10 (FMMD) & \\
|
||||||
0 & Total for INVAMP: & 16 (RFMEA) & \\
|
0 & Total for INVAMP: & 16 ({\XFMEA}) & \\
|
||||||
% & $(3-1) \times (4 + 2 +2)$ & & \\
|
% & $(3-1) \times (4 + 2 +2)$ & & \\
|
||||||
\hline \hline
|
\hline \hline
|
||||||
|
|
||||||
\multicolumn{3}{ |c| } {Inverting Amplifier One stage FMMD Hierarchy: section~\ref{sec:invamp}} \\ \hline
|
\multicolumn{3}{ |c| } {Inverting Amplifier One stage FMMD Hierarchy: section~\ref{sec:invamp}} \\ \hline
|
||||||
0 & INVAMP & 16 & 3 \\
|
0 & INVAMP & 16 & 3 \\
|
||||||
1 & Total for INVAMP: & 16 (FMMD) & \\
|
1 & Total for INVAMP: & 16 (FMMD) & \\
|
||||||
0 & Total for INVAMP: & 16 (RFMEA) & \\
|
0 & Total for INVAMP: & 16 ({\XFMEA}) & \\
|
||||||
\hline
|
\hline
|
||||||
|
|
||||||
\hline
|
\hline
|
||||||
@ -444,8 +447,8 @@ are presented in table~\ref{tbl:firstcc}.
|
|||||||
0 & SEC\_AMP & 16 & 4 \\
|
0 & SEC\_AMP & 16 & 4 \\
|
||||||
3 & DiffAMP & 7 & 4 \\
|
3 & DiffAMP & 7 & 4 \\
|
||||||
3 & Total for DiffAMP & 33 (FMMD)& \\
|
3 & Total for DiffAMP & 33 (FMMD)& \\
|
||||||
0 & Total for DiffAMP: & 80 (RFMEA) & \\
|
0 & Total for DiffAMP: & 80 ({\XFMEA}) & \\
|
||||||
% & Differencing Amplifier: & RFMEA 80-16 = 74 & \\
|
% & Differencing Amplifier: & {\XFMEA} 80-16 = 74 & \\
|
||||||
% & & & \\
|
% & & & \\
|
||||||
\hline
|
\hline
|
||||||
\hline
|
\hline
|
||||||
@ -459,7 +462,7 @@ are presented in table~\ref{tbl:firstcc}.
|
|||||||
3 & FivePoleLP & 20 & 4 \\
|
3 & FivePoleLP & 20 & 4 \\
|
||||||
3 & Total for FivePoleLP & 82 (FMMD)& \\
|
3 & Total for FivePoleLP & 82 (FMMD)& \\
|
||||||
% & 20+48+10+4 & & \\
|
% & 20+48+10+4 & & \\
|
||||||
0 & Total for FivePoleLP & 384 (RFMEA) & \\
|
0 & Total for FivePoleLP & 384 ({\XFMEA}) & \\
|
||||||
% & $(13-1) \times (3 \times 4 + 10 \times 2)$ & & \\ \hline
|
% & $(13-1) \times (3 \times 4 + 10 \times 2)$ & & \\ \hline
|
||||||
\hline
|
\hline
|
||||||
|
|
||||||
@ -470,7 +473,7 @@ are presented in table~\ref{tbl:firstcc}.
|
|||||||
The complexity comparison figures for the example circuits in chapter~\ref{sec:chap5} show
|
The complexity comparison figures for the example circuits in chapter~\ref{sec:chap5} show
|
||||||
that for the non trival examples, as we
|
that for the non trival examples, as we
|
||||||
use more levels in the FMMD hierarchy, the performance
|
use more levels in the FMMD hierarchy, the performance
|
||||||
gain over RFMEA becomes apparent. %for increasing complexity the performance benefits from FMMD are apparent.
|
gain over {\XFMEA} becomes apparent. %for increasing complexity the performance benefits from FMMD are apparent.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
@ -481,7 +484,7 @@ The Bubba oscillator example (see section~\ref{sec:bubba}) was chosen because it
|
|||||||
signal path. It was also analysed twice, once by
|
signal path. It was also analysed twice, once by
|
||||||
{na\"{\i}vely} using the first {\fgs} identified, and secondly by de-composing
|
{na\"{\i}vely} using the first {\fgs} identified, and secondly by de-composing
|
||||||
the circuit further.
|
the circuit further.
|
||||||
We use these two analyses to compare the effect on comparison complexity (see table~\ref{tbl:bubbacc}) with that of RFMEA.
|
We use these two analyses to compare the effect on comparison complexity (see table~\ref{tbl:bubbacc}) with that of {\XFMEA}.
|
||||||
%
|
%
|
||||||
\begin{table}
|
\begin{table}
|
||||||
\label{tbl:bubbacc}
|
\label{tbl:bubbacc}
|
||||||
@ -493,7 +496,7 @@ We use these two analyses to compare the effect on comparison complexity (see ta
|
|||||||
\textbf{Level} & \textbf{Component} & \textbf{Comparison} & \textbf{of derived} \\
|
\textbf{Level} & \textbf{Component} & \textbf{Comparison} & \textbf{of derived} \\
|
||||||
& & & \textbf{failure modes} \\
|
& & & \textbf{failure modes} \\
|
||||||
%\hline \hline
|
%\hline \hline
|
||||||
%\multicolumn{3}{ |c| }{Complexity Comparison against RFMEA for examples in Chapter~\ref{sec:chap5}} \\
|
%\multicolumn{3}{ |c| }{Complexity Comparison against {\XFMEA} for examples in Chapter~\ref{sec:chap5}} \\
|
||||||
%\hline \hline
|
%\hline \hline
|
||||||
|
|
||||||
|
|
||||||
@ -516,7 +519,7 @@ We use these two analyses to compare the effect on comparison complexity (see ta
|
|||||||
2 & Total for BUBBA: & 328 (FMMD) & \\
|
2 & Total for BUBBA: & 328 (FMMD) & \\
|
||||||
% R&C OPAMPS
|
% R&C OPAMPS
|
||||||
% 14 components so 13 \times ( (10*2) (4*4) )
|
% 14 components so 13 \times ( (10*2) (4*4) )
|
||||||
0 & Total for BUBBA: & 468 (RFMEA) & \\
|
0 & Total for BUBBA: & 468 ({\XFMEA}) & \\
|
||||||
% & $(3-1) \times (4 + 2 +2)$ & & \\
|
% & $(3-1) \times (4 + 2 +2)$ & & \\
|
||||||
\hline \hline
|
\hline \hline
|
||||||
|
|
||||||
@ -538,7 +541,7 @@ We use these two analyses to compare the effect on comparison complexity (see ta
|
|||||||
%Level 4: 2 == 2
|
%Level 4: 2 == 2
|
||||||
%
|
%
|
||||||
1 & Total for BUBBA: & 37 (FMMD) & \\
|
1 & Total for BUBBA: & 37 (FMMD) & \\
|
||||||
0 & Total for BUBBA: & 468 (RFMEA) & \\
|
0 & Total for BUBBA: & 468 ({\XFMEA}) & \\
|
||||||
\hline
|
\hline
|
||||||
|
|
||||||
\hline
|
\hline
|
||||||
@ -567,7 +570,7 @@ by more than a factor of ten.
|
|||||||
\textbf{Level} & \textbf{Component} & \textbf{Comparison} & \textbf{of derived} \\
|
\textbf{Level} & \textbf{Component} & \textbf{Comparison} & \textbf{of derived} \\
|
||||||
& & & \textbf{failure modes} \\
|
& & & \textbf{failure modes} \\
|
||||||
%\hline \hline
|
%\hline \hline
|
||||||
%\multicolumn{3}{ |c| }{Complexity Comparison against RFMEA for examples in Chapter~\ref{sec:chap5}} \\
|
%\multicolumn{3}{ |c| }{Complexity Comparison against {\XFMEA} for examples in Chapter~\ref{sec:chap5}} \\
|
||||||
%\hline \hline
|
%\hline \hline
|
||||||
|
|
||||||
|
|
||||||
@ -594,7 +597,7 @@ by more than a factor of ten.
|
|||||||
2 & Total for {\sd}: & 55 (FMMD) & \\
|
2 & Total for {\sd}: & 55 (FMMD) & \\
|
||||||
% R&C OPAMPS
|
% R&C OPAMPS
|
||||||
% 14 components so (10-1) *
|
% 14 components so (10-1) *
|
||||||
0 & Total for {\sd}: & 225 (RFMEA) & \\
|
0 & Total for {\sd}: & 225 ({\XFMEA}) & \\
|
||||||
|
|
||||||
\hline \hline
|
\hline \hline
|
||||||
|
|
||||||
@ -1211,6 +1214,31 @@ We can express their probabilities as $P(B_4) = P(B_1 \cap B_3)$ and $P(B_5) = P
|
|||||||
|
|
||||||
\subsection{Problems in choosing membership of functional groups}
|
\subsection{Problems in choosing membership of functional groups}
|
||||||
|
|
||||||
|
The choice of components for {\fgs} is one to be made by the analyst.
|
||||||
|
The guiding principle it to choose components that are functionally adjacent
|
||||||
|
and try to create the smallest groups possible.
|
||||||
|
There are some mistakes that an analyst could make when choosing the members
|
||||||
|
of functional groups. These are
|
||||||
|
\begin{itemize}
|
||||||
|
\item Choosing components that are not functionally adjacent --- i.e. components that do not work together to perform a specific function,
|
||||||
|
\item Not including components that may have side effects on the {\fg}, but are not obviously connected.
|
||||||
|
\end{itemize}
|
||||||
|
|
||||||
|
If we were to deliberately choose a `bad' {\fg} we would find that,
|
||||||
|
on analysing it, the component failure modes would not converge to common
|
||||||
|
symptoms.
|
||||||
|
%
|
||||||
|
This would be because, with functionally adjacent
|
||||||
|
components, their failures often cause common failure symptoms for the {\fg}.
|
||||||
|
%
|
||||||
|
With components that are not interacting, we are unlikely to see
|
||||||
|
this convergence of symptoms.
|
||||||
|
%
|
||||||
|
%
|
||||||
|
This property could be of use in future automated FMMD tools
|
||||||
|
to warn of potentially poorly chosen {\fgs}.
|
||||||
|
|
||||||
|
|
||||||
\subsubsection{Side Effects: A Problem for FMMD analysis}
|
\subsubsection{Side Effects: A Problem for FMMD analysis}
|
||||||
\label{sec:sideeffects}
|
\label{sec:sideeffects}
|
||||||
A problem with modularising according to functionality is that we can have component failures that would % poss split infinitive
|
A problem with modularising according to functionality is that we can have component failures that would % poss split infinitive
|
||||||
|
@ -132,7 +132,8 @@ failure statistics, we calculate the reliability of this circuit.
|
|||||||
The formula for given in MIL-HDBK-217F\cite{mil1991}[9.2] for a generic fixed film non-power resistor
|
The formula for given in MIL-HDBK-217F\cite{mil1991}[9.2] for a generic fixed film non-power resistor
|
||||||
is reproduced in equation \ref{resistorfit}. The meanings
|
is reproduced in equation \ref{resistorfit}. The meanings
|
||||||
and values assigned to its co-efficients are described in table \ref{tab:resistor}.
|
and values assigned to its co-efficients are described in table \ref{tab:resistor}.
|
||||||
\glossary{name={FIT}, description={Failure in Time (FIT). The number of times a particular failure is expected to occur in a $10^{9}$ hour time period.}}
|
\glossary{name={FIT}, description={Failure in Time (FIT). The number of times a particular
|
||||||
|
failure is expected to occur in a $10^{9}$ hour time period.}}
|
||||||
|
|
||||||
|
|
||||||
\fmodegloss
|
\fmodegloss
|
||||||
|
@ -55,6 +55,12 @@
|
|||||||
\newcommand{\irl}{in~real~life}
|
\newcommand{\irl}{in~real~life}
|
||||||
\newcommand{\enc}{\ensuremath{\stackrel{enc}{\longrightarrow}}}
|
\newcommand{\enc}{\ensuremath{\stackrel{enc}{\longrightarrow}}}
|
||||||
\newcommand{\pin}{\ensuremath{\stackrel{pi}{\longleftrightarrow}}}
|
\newcommand{\pin}{\ensuremath{\stackrel{pi}{\longleftrightarrow}}}
|
||||||
|
%
|
||||||
|
% OK after about 3 years its not rigorous FMEA (RFMEA) anymore, oh no, its Exhaustive FMEA
|
||||||
|
% but since the fuckers might change it yet again, I am making this a macro.
|
||||||
|
\newcommand{\XFMEA}{XFMEA}
|
||||||
|
%
|
||||||
|
|
||||||
%\newcommand{\pic}{\em pure~intersection~chain}
|
%\newcommand{\pic}{\em pure~intersection~chain}
|
||||||
\newcommand{\pic}{\emp pair-wise~intersection~chain}
|
\newcommand{\pic}{\emp pair-wise~intersection~chain}
|
||||||
\newcommand{\wrt}{\emp with~respect~to}
|
\newcommand{\wrt}{\emp with~respect~to}
|
||||||
|
@ -64,7 +64,7 @@
|
|||||||
% numbers at outer edges
|
% numbers at outer edges
|
||||||
\pagenumbering{arabic} % Arabic page numbers hereafter
|
\pagenumbering{arabic} % Arabic page numbers hereafter
|
||||||
\cfoot{Page \thepage\ of \pageref{LastPage}}
|
\cfoot{Page \thepage\ of \pageref{LastPage}}
|
||||||
\lfoot{University of Brighton 2012} %% Year keeps fucking incrementing
|
\lfoot{University of Brighton} %% Year keeps fucking incrementing
|
||||||
\rfoot{R.P.Clark \today}
|
\rfoot{R.P.Clark \today}
|
||||||
\lhead{Failure Mode Modular De-Composition}
|
\lhead{Failure Mode Modular De-Composition}
|
||||||
\rhead{Ph.D Thesis}
|
\rhead{Ph.D Thesis}
|
||||||
|
Loading…
Reference in New Issue
Block a user