OK now need to do working out for the final two stages

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Robin Clark 2012-01-06 17:51:58 +00:00
parent 0e52a01620
commit eab783bdb2
2 changed files with 32 additions and 8 deletions

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@ -35,6 +35,11 @@ Not a document to be proof read.
Proof of analysis concept. Proof of analysis concept.
Function $fm$ applied to a component returns its failure modes. Function $fm$ applied to a component returns its failure modes.
The circuits specified are not typical saftey critical circuitry which usually
has both redundancy and self~checking and/or diagnostic features build in.
These are examples of the FMMD methodology being applied to some standard electronic circuits.
\end{abstract} \end{abstract}
\maketitle \maketitle
\tableofcontents \tableofcontents
@ -457,7 +462,7 @@ We merely have to choose a top level event and work down using $XOR$ gates.
This circuit performs poorly from a safety point of view. This circuit performs poorly from a safety point of view.
Its failure modes could be indistinguishable from valid readings (especially Its failure modes could be indistinguishable from valid readings (especially
wihen it becomes a V2 follower). when it becomes a V2 follower).
\begin{figure}[h] \begin{figure}[h]
\centering \centering
@ -773,10 +778,20 @@ This circuit is described in the Analog Applications Journal~\cite{bubba}.
The circuit uses four 45 degree phase shifts, and an inverting amplifier to provide The circuit uses four 45 degree phase shifts, and an inverting amplifier to provide
gain and the final 180 degrees of phase shift (making a total of 360 degrees of phase shift). gain and the final 180 degrees of phase shift (making a total of 360 degrees of phase shift).
We identifiy three functional groups, the inverting amplifer (analysed in section~\ref{fig:invamp}), From a fault finding perspective this circuit is less than ideal.
a 45 degree phase shifter (a {$10k\Omega$} resistor and a $10nF$ capacitor) and a noninverting buffer The signal path is circular (its a positive feedback circuit) and most failures would simply cause the output to stop oscillating.
However, FMMD is a bottom -up analysis methodology and we can therefore still identify
{\fgs} and apply analysis from a failure mode perspective.
If we were to analyse this circuit without modularisation, we have 14 components with
($4.4 +10.2 = 36$) failure modes . Applying equation~\ref{eqnrd2} gives a complexity comparison figure of $13.36=468$.
The reduce the complexity required to analyse this circuit we apply FMMD and start by determining {\fgs}.
We identify three types functional groups, an inverting amplifier (analysed in section~\ref{fig:invamp}),
a 45 degree phase shifter (a {$10k\Omega$} resistor and a $10nF$ capacitor) and a non-inverting buffer
amplifier. We can name these $INVAMP$, $PHS45$ and $NIBUFF$ respectively. amplifier. We can name these $INVAMP$, $PHS45$ and $NIBUFF$ respectively.
We can use these {\fgs} to describe the circuit in block diagram form, as in figure ~\ref{fig:bubbablock}. We can use these {\fgs} to describe the circuit in block diagram form, see figure ~\ref{fig:bubbablock}.
\begin{figure}[h] \begin{figure}[h]
\centering \centering
@ -838,7 +853,7 @@ $$ fm(NIBUFF) = fm(OPAMP) = \{L\_{up}, L\_{dn}, Noop, L\_slew \} $$
% describe what we are doing, a buffered 45 degree phase shift element % describe what we are doing, a buffered 45 degree phase shift element
\subsection{Bringing the functional Groups Together: The `Bubba' Oscillator.} \subsection{Bringing the functional Groups Together: FMMD model of the `Bubba' Oscillator.}
We could at this point bring all the {\dcs} together into one large functional We could at this point bring all the {\dcs} together into one large functional
group (see figure~\ref{fig:poss1finalbubba}) group (see figure~\ref{fig:poss1finalbubba})
@ -848,7 +863,9 @@ The capactior and 180 degree inverting amplifier, form a {\fg}
providing an amplified 225 degree phase shift, which we can call $PHS225AMP$. providing an amplified 225 degree phase shift, which we can call $PHS225AMP$.
% %
We could also merge the $NIBUFF$ and $PHS45$ We could also merge the $NIBUFF$ and $PHS45$
{\dcs} into a {\fg} and the resulant derived component from this we could call a $BUFF45$, and then with those three, form a $PHS135BUFFERED$ functional group -- with the remaining $PHS45$ and the $INVAMP$ in a second group $PHS225AMP$, {\dcs} into a {\fg} and the resulant derived component from this we could call a $BUFF45$,
and then with those three, form a $PHS135BUFFERED$
functional group---with the remaining $PHS45$ and the $INVAMP$ (re-used from section~\ref{sec:invamp})in a second group $PHS225AMP$---
and then merge $PHS135BUFFERED$ and $PHS225AMP$ in a final stage (see figure~\ref{fig:poss2finalbubba}) and then merge $PHS135BUFFERED$ and $PHS225AMP$ in a final stage (see figure~\ref{fig:poss2finalbubba})
@ -1239,7 +1256,14 @@ in component ${c_i}$, is given by
\end{equation} \end{equation}
This can be simplified if we can determine the total number of failure modes in the system $K$, (i.e. $ K = \sum_{n=1}^{|G|} {|fm(c_n)|}$); This can be simplified if we can determine the total number of failure modes in the system $K$, (i.e. $ K = \sum_{n=1}^{|G|} {|fm(c_n)|}$);
equation~\ref{eqn:CC} becomes $$ CC(\FG) = K.(|\FG|-1).$$ equation~\ref{eqn:CC} becomes
%$$
\begin{equation}
\label{eqn:rd2}
CC(\FG) = K.(|\FG|-1).
\end{equation}
%$$
%Equation~\ref{eqn:rd} can also be expressed as %Equation~\ref{eqn:rd} can also be expressed as
% %
% \begin{equation} % \begin{equation}

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@ -5,7 +5,7 @@
\usepackage{tikz} \usepackage{tikz}
\usetikzlibrary{shapes,snakes} \usetikzlibrary{shapes,snakes}
\usetikzlibrary{shapes.gates.logic.US,trees,positioning,arrows} \usetikzlibrary{shapes.gates.logic.US,trees,positioning,arrows}
\usepackage{subfigure} %\usepackage{subfigure}
\usepackage{amsfonts,amsmath,amsthm} \usepackage{amsfonts,amsmath,amsthm}
\usepackage{algorithm} \usepackage{algorithm}
\usepackage{algorithmic} \usepackage{algorithmic}