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@ -101,7 +101,7 @@ FMEA is used principally in manufacturing.
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Each defect is assessed by its cost to repair and its frequency. %, using a
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%failure mode ratio.
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A list of failures and their cost is generated.
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It is easy to identify single component failure to system failure scenarios
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It is easy to identify single component failure to system failure scenarios,
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and an estimate of product reliability can be calculated. It cannot focus on
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component interactions that cause system failure modes or determine potential
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problems from simultaneous failure modes. It does not consider environmental
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@ -139,7 +139,7 @@ event, this leads to repeated work, with limited ability for cross checking/mode
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\paragraph{State Explosion problem}
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The bottom -up techniques all suffer from a problem of state explosion.
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To perform the analysis rigorously, we need to consider the effect
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To perform the analysis rigorously, we would need to consider the effect
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of a component failure against all other components. Adding environmental
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and operational states further increases this effect.
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@ -282,6 +282,24 @@ for its results, such as error causation trees.%, reliability and safety statis
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% of sub-systems the SYSTEM.
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\section{The proposed Methodology}
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\label{fmmdproc}
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The proposed methodology is a bottom-up process
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starting with base~components.
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These are collected into functional groups
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and each component failure mode (and optionally combinations) are considered in the
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context of the {\fg}. These are termed `test~cases'. For each test~case
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there will be a corresponding failure mode, from the perspective of the {\fg}.
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A symptom collection stage is then applied. Here common symptoms are collected
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from the results of the test~cases.Diagram1
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With a collection of the {\fg} failure symptoms, we can now create a {\dc}.
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The failure modes of this new {\dc} are the symptoms of the {\fg} it was derived from.
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By using {\dcs} in higher level functional groups, a hierarchy can be built representing
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the failure mode behaviour of a SYSTEM.
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\subsection{Environmental Conditions, Operational States}
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Any real world sub-system will exist in a variable environment
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@ -362,24 +380,6 @@ Operational states are conditions that apply to some functional groups, not indi
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%DEVELOP UML MODELS
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\section{The proposed Methodology}
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\label{fmmdproc}
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The proposed methodology is a bottom-up process
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starting with base~components.
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These are collected into functional groups
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and each component failure mode (and optionally combinations) are considered in the
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context of the {\fg}. These are termed `test~cases'. For each test~case
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there will be a corresponding failure mode, from the perspective of the {\fg}.
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A symptom collection stage is then applied. Here common symptoms are collected
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from the results of the test~cases.Diagram1
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With a collection of the {\fg} failure symptoms, we can now create a {\dc}.
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The failure modes of this new {\dc} are the symptoms of the {\fg} it was derived from.
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By using {\dcs} in higher level functional groups, a hierarchy can be built representing
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the failure mode behaviour of a SYSTEM.
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\subsection{FMMD analysis Example: A Voltage/Potential Divider}
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\begin{figure}
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\centering
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@ -389,7 +389,7 @@ the failure mode behaviour of a SYSTEM.
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\label{fig:pd}
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\end{figure}
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We consider here an example functional group, the potential divider
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We consider here an example functional group, the potential divider\footnote{A commonly used configuration in electronics to provide specific voltage levels}
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which consists of two resistors used to provide a voltage
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intermediate of its supply and ground rails.
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%It consists of two resistors.
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@ -440,10 +440,8 @@ $R1$ has failure modes $\{R1\_OPEN, R1\_SHORT\}$ and $R2$ has failure modes $\{R
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%\ifthenelse {\boolean{dag}}
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%{
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Modelling the two resistors as a functional group, we present this as a directed graph.
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%failure modes, taken from the components R1 and R2,
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%in the potential divider, shown
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in figure \ref{fig:fg1dag}.
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Modelling the two resistors as a functional group, we present this as a directed graph
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(see figure \ref{fig:fg1dag}).
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\begin{figure}[h+]
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\centering
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@ -507,7 +505,7 @@ on the potential dividers' operation. For instance
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were the resistor $R_1$ to go open, the circuit would not be grounded and the
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voltage output from it would be the +ve supply rail.
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This would mean the symptom of the failed potential divider, would be that it
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gives an output high voltage reading. We can now consider the {\fg}
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gives an output high voltage. We can now consider the {\fg}
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as a component in its own right, and its symptoms as its failure modes.
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From table \ref{pdfmea} we can see that resistor
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@ -625,6 +623,10 @@ We avoided the state explosion problem of having to
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check $R1$ and $R2$ against all other components in the system they may belong to.
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Also, by modularising the circuit as a {\dc}, we have reduced the number of errors we need to consider at higher levels
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of analysis.
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Using {\dcs} in higher level {\fgs} we can build a hierarchy to represent the failure mode behaviour
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of complete systems.
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% \subsection{Re-Factoring the UML Model}
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%
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% The UML models thus far % in this
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@ -15,10 +15,11 @@
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\setboolean{paper}{true} % boolvar=true or false
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\newboolean{pld}
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\setboolean{pld}{false} % boolvar=true or false : draw analysis using propositional logic diagrams
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\setboolean{pld}{true} % boolvar=true or false : draw analysis using propositional logic diagrams
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\newboolean{dag}
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\setboolean{dag}{true} % boolvar=true or false : draw analysis using directed acylic graphs
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\def\layersep{2.5cm}
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related_papers_books/steam.pdf
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related_papers_books/steam.pdf
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