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Added SRDO and SROVT concepts from caninauto

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Robin Clark 2010-09-13 07:31:10 +01:00
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statistics/statistics.tex
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@ -47,6 +47,28 @@ Impact of boiler going down, no CO2 primary coolant available, possible reactor
For the Brewery, safety is of the highest importance.
For the Nuclear power station
\section{Terms and Concepts in // Safety Critical Engineering}
\subsection{Safety Relevant Data Object}
A Safety Relevant Data Object (SRDO)\cite{caninauto}, is a data structure describing the status of
a particular feature or attribute of a safety critical system.
For instance, in a burner this could be a flame signal value, or in a nuclear powerstation
the measure neutron flux.
\subsection{Safety relevant Object Validation Time}
Safety times can be given for SRDO's; these are termed Safety Related Object Validation Times (SROVT's)\cite{caninauto}. For instance were
a flame to fail in operation in a gas burner
standards state that the gas may not continue to be fed into the
furnace for more than three seconds \cite{en298}.
We can say that the SROVT for a flame signal in a gas burner is 3 seconds.
\subsection{Single and Double Failure Modes}
A Safety critical system must self check within the relevant SROVT's.
On detecting a failure mode it must react appropriately.
Consider the case though where two failures occurr within the
time windows of their SROVT's. We can term this a double simultaneous failure mode.
To take an extreme example, were the checking function/mechanism and the object under supervision
to fail within the SROVT, it may be impossible to detect the failure.
\section{Interfacing}
Mech - elec - sw