From a6715889f059eb5ec46faf597bcb8f97b5dc2a01 Mon Sep 17 00:00:00 2001 From: "Robin P. Clark" Date: Tue, 17 Sep 2013 09:55:35 +0100 Subject: [PATCH] conclusion: prob of composition of standalone modules/{\fgs} --- submission_thesis/CH8_Conclusion/copy.tex | 44 +++++++++++++++++++++++ 1 file changed, 44 insertions(+) diff --git a/submission_thesis/CH8_Conclusion/copy.tex b/submission_thesis/CH8_Conclusion/copy.tex index c2ceef6..eab3223 100644 --- a/submission_thesis/CH8_Conclusion/copy.tex +++ b/submission_thesis/CH8_Conclusion/copy.tex @@ -162,6 +162,50 @@ in a way that is compatible with FMEDA/EN61508. \fmmdglossFIT +\subsection{Composition of {\fgs}.} + +The choice of components for a {\fg} are that they are components that +work together to perform a pre-defined function. +% +The choice for {\fg} membership is made by the analyst. +% +The act of choosing component to comprise a {\fg} +raises questions about the circuit under investigation. +% +Ideally {\fgs} will be able to act as standalone modules. +% +An inverting amplifier configuration, or a low pass filter are good examples of these. +% +These have clear inputs and outputs, and are resilient to what they are connected to at +the output (in electronics terms they have high output impedance). +% +In defining members for {\fgs} he analyst is forced to consider the interfaces between elements +of circuitry to identify modules. +% +Consider the resistor capacitor low pass stage first looked at in example~\ref{sec:lp}. %\label{sec:lp} +% +This circuit element, while applying a filtering effect, has a low output impedance. +% +With a simple OpAmp buffer amplifier it becomes an effective, high impedance output, standalone module. +% +These two elements, the resistor capacitor low pass stage and the OpAmp +are good candidates therefore, for being considered as a standalone module, and thus a {\fg}. +% +However, different analysts may choose different {\fgs} +when analysing the same circuit. +% +This means that {\fgs} are not guaranteed to be unique. +% +This apparent anomaly is explored in the examples~\ref{sec:invamp},~\ref{sec:bubba} were different +structure of the FMMD hierarchy are used to analyse the same circuitry. +% +The same system level failure modes are obtained, but the more de-composed examples +offer better performance in terms of comparison complexity. +% +Further work may be required to apply justification for the choice of the membership in {\fgs}. +% +For software already written this problem does not exist as the choice of membership has already been made by the programmer. + % \subsection{Deriving FTA diagrams from FMMD models} \label{sec:fta}