doh forgot to comiit

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Robin Clark 2011-06-17 17:42:49 +01:00
parent 9e26770d38
commit 5cca1a1311
3 changed files with 32 additions and 29 deletions

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

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@ -15,10 +15,11 @@
\setboolean{paper}{true} % boolvar=true or false \setboolean{paper}{true} % boolvar=true or false
\newboolean{pld} \newboolean{pld}
\setboolean{pld}{false} % boolvar=true or false : draw analysis using propositional logic diagrams \setboolean{pld}{true} % boolvar=true or false : draw analysis using propositional logic diagrams
\newboolean{dag} \newboolean{dag}
\setboolean{dag}{true} % boolvar=true or false : draw analysis using directed acylic graphs \setboolean{dag}{true} % boolvar=true or false : draw analysis using directed acylic graphs
\def\layersep{2.5cm} \def\layersep{2.5cm}

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