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CH5 AF comments

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Robin Clark 2013-09-18 08:57:39 +01:00
parent 9bec687779
commit 2f17ed2ec8
2 changed files with 17 additions and 11 deletions
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3
submission_thesis/CH2_FMEA/copy.tex
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@ -429,8 +429,11 @@ investigations.
\fmmdglossOPAMP
The symptom for this is given as a low slew rate.
%
Slew rate for a circuit/component is the rate at which it changes an output voltage level (i.e. $\frac{\delta V}{\delta t} $).
%
This means that the op-amp will not react quickly to changes on its input terminals.
%
%
This is a failure symptom that may not be of concern in a slow responding system like an
instrumentation amplifier. However, where higher frequencies are being processed,
a signal may be lost entirely.

25
submission_thesis/CH5_Examples/copy.tex
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@ -78,9 +78,7 @@ A valid range for the output value of this circuit is assumed.
%and voltages higher than a given threshold considered as HIGH.
%
Because the amplifier inverts and the input is guaranteed positive any
output voltage above or equal to zero would be erroneous.
%
This would be an `$AMP_{HIGH}$' failure symptom.
output voltage above or equal to zero would be erroneous i.e. an `$AMP_{HIGH}$' failure symptom.
%
A threshold would be determined for an `$AMP_{LOW}$' failure symptom (i.e. the output voltage more negative than expected). % error given the expected input range.
%
@ -183,7 +181,8 @@ The final stage of analysis for this amplifier, is made by
by forming a {\fg} with the OpAmp and the new {\dc} $IPD$.
%
\begin{table}[h+]
\caption{Inverting Amplifier: Single failure analysis using the $PD$ {\dc}}
\centering
\caption{Inverting Amplifier: Single failure analysis using the $IPD$ {\dc}}
\begin{tabular}{|| l | l | c | c | l ||} \hline
%\textbf{Failure Scenario} & & \textbf{Inverted Amp Effect} & & \textbf{Symptom} \\ \hline
\textbf{Failure} & & \textbf{Inverted Amp. Effect} & & \textbf{Symptom} \\
@ -460,7 +459,10 @@ This means R3 R4 is not a fixed potential divider, with R4 being on the positive
%
It could be at either polarity. % (i.e. the other way around R4 could be the negative side).
%
Here it is more intuitive to model the resistors not as a potential divider, but individually.
Here, even though R3 and R4 are used as a potential divider,
it could be either inverted or non-inverted according to the voltages on the inputs.
Therefore the resistors cannot modelled as a potential divider, but must be placed in the {\fg}
with the OpAmp and analysed.
%This means we are either going to
%get a high or low reading if R3 or R4 fail.
@ -661,6 +663,7 @@ The first order low pass filter is analysed in table~\ref{tbl:firstorderlpass}.\
\begin{table}[h+]
\centering
\caption{FirstOrderLP: Failure Mode Effects Analysis: Single Faults} % title of Table
\label{tbl:firstorderlpass}
@ -821,7 +824,7 @@ and these are marked on the circuit schematic in figure~\ref{fig:circuit2002_FIV
\label{fig:circuit2002_FIVEPOLE}
\end{figure}
%
\pagebreak[4]
%\pagebreak[4]
%
So the final {\fg} will consist of the derived components $\{ LP1, SKLP_1, SKLP_2 \}$.
%
@ -1214,7 +1217,7 @@ increases the potential for re-use. % of pre-analysed {\dcs}.
%
A finer grained model---with potentially more hierarchy stages---also means that
%more work, or
more reasoning stages have been used in the analysis.
more reasoning stages, i.e. FMMD analysis stages with their associated analysis reports, have been used in the analysis.
% HTR The more we can modularise, the more we decimate the $O(N^2)$ effect
% HTR of complexity comparison.
%
@ -1227,7 +1230,7 @@ However, it involves a large reasoning distance, the final stage
having 24 failure modes to consider against each of the other seven {\dcs}.
A finer grained approach produces more potentially re-usable {\dcs} and
involves several stages with lower reasoning distances.
The lower reasoning distances, or complexity comparision figures are given in the metrics chapter~\ref{sec:chap7}
The lower reasoning distances, or complexity comparison figures are given in the metrics chapter~\ref{sec:chap7}
at section~\ref{sec:bubbaCC}.
These show that the finer grained models also benefit from lower reasoning distances for the failure mode model.
@ -1731,7 +1734,7 @@ expected voltages for failure mode and temperature reading purposes.
\begin{equation}
\label{eqn:vd}
V_{out} = V_{in}.\frac{Z2}{Z2+Z1}
V_{out} = V_{in}.\frac{Z_2}{Z_2+Z_1}
\end{equation}
\subsection{Safety case for 4 wire circuit: Detailed calculations}
@ -1843,8 +1846,8 @@ As the voltage over $R_3$ is relative (a design feature to eliminate resistance
the current can be calculated by reading
the voltage over the known resistor
$R2$.\footnote{To calculate the resistance of the Pt100 we need the current flowing though it.
This can be determined via Ohms law applied to $R_2$, $V=IR$, $I=\frac{V}{R_2}$,
and then using $I$, with $I$, $R_{3} = \frac{V_{R3}}{I}$.}
This can be determined via Ohms law applied to $R_2$, $V=I R_2$, $I=\frac{V}{R_2}$,
and then using $I$, $R_{3} = \frac{V_{R3}}{I}$.}
As these calculations are performed by Ohms law, which is linear, the accuracy of the reading
will be determined by the accuracy of $R_2$ and $R_{3}$.
%It is reasonable to