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Robin Clark 2011-03-16 10:01:07 +00:00
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logic_diagram/logic_diagram.tex
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@ -961,12 +961,15 @@ European Norm EN298~\cite{en298}[Sn.9] states that if a burner controller is in
and has ordered a shutdown) a secondary fault cannot be allowed to put the equipment under control (the burner) into a dangerous state. and has ordered a shutdown) a secondary fault cannot be allowed to put the equipment under control (the burner) into a dangerous state.
To cover this rigorously, we must consider all faults that can lead to a LOCKOUT condition To cover this rigorously, we must consider all faults that can lead to a LOCKOUT condition
and then look for others that could put the system into a dangerous state after the LOCKOUT. and then look for others that could put the system into a dangerous state after the LOCKOUT.
In practise, this would be a gigantic (as probably impossible task). In practise, this would be a gigantic (and probably impossible task).
What we can consider though, are all faults being double simultaneous in the FMMD What we can consider though, are all faults being double simultaneous in the FMMD
methodology, because we need only look for the double failure modes within each functional group. methodology, because we need only look for the double failure modes within each functional group.
Because we are looking for double failure modes within small groups Because we are looking for double failure modes within small groups
the number of checks cross product factor is drastically reduced. the number of checks cross product factor is drastically reduced.
So drastically reduced that it makes it a practical possibility. So drastically reduced, that it makes full failure more coverage
for double simultaneous failures, a practical possibility.
% Do we need an order of equation here ???
\paragraph{Covering Double faults in a PLD Diagram} \paragraph{Covering Double faults in a PLD Diagram}
Because we are allowed to repeat contours in a PLD diagram, Because we are allowed to repeat contours in a PLD diagram,
we can arrange them in a matrix like configuration as in figure \ref{fig:doublesim}. we can arrange them in a matrix like configuration as in figure \ref{fig:doublesim}.