ref to voltage divider
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pt100/pt100.tex
102
pt100/pt100.tex
@ -52,8 +52,6 @@ look-up tables or a suitable polynomial expression.
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\end{figure}
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\end{figure}
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The voltage ranges we expect from this three stage potential divider
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The voltage ranges we expect from this three stage potential divider
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are shown in figure \ref{fig:pt100vrange}. Note that there is
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are shown in figure \ref{fig:pt100vrange}. Note that there is
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an expected range for each reading, for a given temperature span.
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an expected range for each reading, for a given temperature span.
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@ -155,52 +153,15 @@ 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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\pagebreak
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% \subsection{Single Fault Modes as PLD}
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%
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% The component~failure~modes in table \ref{ptfmea} can be represented as contours
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% on a PLD diagram. Each test case, or analysis into the effects of the component failure
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% caused by the component~failure is represented by an labelled asterisk.
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%
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%
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% \begin{figure}[h]
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% \centering
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% \includegraphics[width=400pt,bb=0 0 518 365,keepaspectratio=true]{./pt100/pt100_tc.jpg}
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% % pt100_tc.jpg: 518x365 pixel, 72dpi, 18.27x12.88 cm, bb=0 0 518 365
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% \caption{PT100 Component Failure Modes}
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% \label{fig:pt100_tc}
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% \end{figure}
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%
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% This circuit supplies two results, sense+ and sense- voltage readings.
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% To establish the valid voltage ranges for these, and knowing our
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% valid tempperature range for this example ({0\oc} .. {300\oc}) we can calculate
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% valid voltage reading ranges by using the standard voltage divider equation \ref{eqn:vd}
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% for the circuit shown in figure \ref{fig:vd}.
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\begin{figure}[h]
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\centering
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\includegraphics[width=100pt,bb=0 0 183 170,keepaspectratio=true]{./pt100/voltage_divider.png}
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% voltage_divider.png: 183x170 pixel, 72dpi, 6.46x6.00 cm, bb=0 0 183 170
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\caption{Voltage Divider}
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\label{fig:vd}
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\end{figure}
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%The looking at figure \ref{fig:vd} the standard voltage divider formula (equation \ref{eqn:vd}) is used.
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\begin{equation}
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\label{eqn:vd}
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V_{out} = V_{in}.\frac{Z2}{Z2+Z1}
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\end{equation}
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\subsection{Range and PT100 Calculations}
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\subsection{Range and PT100 Calculations}
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\label{pt100temp}
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\label{pt100temp}
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PT100 resistors are designed to
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PT100 resistors are designed to
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have a resistance of \ohms{100} at 0 \oc \cite{eurothermtables}.
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have a resistance of \ohms{100} at {0\oc} \cite{aoe},\cite{eurothermtables}.
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A suitable `wider than to be expected range' was considered to be {0\oc} to {300\oc}
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A suitable `wider than to be expected range' was considered to be {0\oc} to {300\oc}
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for a given application.
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for a given application.
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According to the Eurotherm PT100
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According to the Eurotherm PT100
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tables \cite{eurothermtables}, this corresponded to the resistances \ohms{60.28}
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tables \cite{eurothermtables}, this corresponded to the resistances \ohms{100}
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and \ohms{212.02} respectively. From this the potential divider circuit can be
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and \ohms{212.02} respectively. From this the potential divider circuit can be
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analysed and the maximum and minimum acceptable voltages determined.
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analysed and the maximum and minimum acceptable voltages determined.
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These can be used as bounds results to apply the findings from the
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These can be used as bounds results to apply the findings from the
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@ -246,48 +207,6 @@ Table \ref{ptbounds} gives ranges that determine correct operation. In fact it c
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for any single error (short or opening of any resistor) this bounds check
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for any single error (short or opening of any resistor) this bounds check
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will detect it.
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will detect it.
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%\vbox{
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%\subsubsection{Calculating Bounds: High Value : HP48 RPL}
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%
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%
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%HP RPL calculator program to take pt100 resistance
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%and convert to voltage and {\adctw} values.
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%
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%\begin{verbatim}
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%<< -> p
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% <<
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% p 2200 + 2200 2200 + p + / 5 * DUP 5
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% / 4096 *
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% >>
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%>>
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%\end{verbatim}
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%}
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%
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%\vbox{
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%\subsubsection{Calculating Bounds: LOW Value : HP48 RPL}
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%
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%
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%HP RPL calculator program to take pt100 resistance
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%and convert to voltage and {\adctw} values.
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%
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%\begin{verbatim}
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%<< -> p
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% <<
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% p 2200 2200 p 2200 + + / 5 * DUP 5
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% / 4096 *
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% >>
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%>>
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%\end{verbatim}
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%}
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%
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%\subsection{Implementation of Four Wire Circuit}
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%
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%A standard 4 wire PT100\cite[pp 992]{aoe} circuit is read by
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%ports on the 12 bit ADC of the PIC18F2523\cite{pic18f2523}.
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%Three readings are taken. A reading to confirm the voltage level
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%over $R_2$ is taken,
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%from which the current can be determined.
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%The two sense lines then give the vo
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\section{Single Fault FMEA Analysis of PT100 Four wire circuit}
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\section{Single Fault FMEA Analysis of PT100 Four wire circuit}
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@ -312,7 +231,22 @@ This circuit supplies two results, sense+ and sense- voltage readings.
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To establish the valid voltage ranges for these, and knowing our
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To establish the valid voltage ranges for these, and knowing our
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valid temperature range for this example ({0\oc} .. {300\oc}) we can calculate
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valid temperature range for this example ({0\oc} .. {300\oc}) we can calculate
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valid voltage reading ranges by using the standard voltage divider equation \ref{eqn:vd}
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valid voltage reading ranges by using the standard voltage divider equation \ref{eqn:vd}
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for the circuit shown in .
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for the circuit shown in figure \ref{fig:vd}.
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\begin{figure}[h]
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\centering
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\includegraphics[width=100pt,bb=0 0 183 170,keepaspectratio=true]{./pt100/voltage_divider.png}
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% voltage_divider.png: 183x170 pixel, 72dpi, 6.46x6.00 cm, bb=0 0 183 170
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\caption{Voltage Divider}
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\label{fig:vd}
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\end{figure}
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%The looking at figure \ref{fig:vd} the standard voltage divider formula (equation \ref{eqn:vd}) is used.
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\begin{equation}
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\label{eqn:vd}
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V_{out} = V_{in}.\frac{Z2}{Z2+Z1}
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\end{equation}
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