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Robin Clark 2010-06-18 08:45:22 +01:00
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pt100/pt100.tex
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@ -807,7 +807,8 @@ in figure \ref{fig:dubsim}.
\clearpage
\subsection{Derived Component : The PT100 Circuit}
The PT100 circuit again, can now be treated as a component in its own right, and has two failure modes,
{\textbf{OUT\_OF\_RANGE}} and {\textbf{FLOATING}}. It can now be represented as a PLD see figure \ref{fig:pt100_doublef}.
{\textbf{OUT\_OF\_RANGE}} and {\textbf{FLOATING}}.
It can now be represented as a PLD see figure \ref{fig:pt100_doublef}.
\begin{figure}[h]
\centering
@ -819,6 +820,13 @@ The PT100 circuit again, can now be treated as a component in its own right, and
\subsection{Statistics}
%%
%% Need to talk abou the `detection time'
%% or `Safety Relevant Validation Time' ref can book
%% EN61508 gives detection calculations to reduce
%% statistical impacts of failures.
%%
If we consider the failure modes to be statistically independent we can calculate
the FIT values for all the failures. The failure mode of concern, the undetectable {\textbf{FLOATING}} condition
requires that resistors $R_1$ and $R_2$ fail. We can multiply the MTTF