diff --git a/fmmd_concept/fmmd_concept.tex b/fmmd_concept/fmmd_concept.tex index a6c3e97..583556e 100644 --- a/fmmd_concept/fmmd_concept.tex +++ b/fmmd_concept/fmmd_concept.tex @@ -275,6 +275,7 @@ The four methodologies in current use are discussed briefly below. \glossary{name={FTA},description={Fault Tree Analysis}} This, like all top~down methodologies introduces the very serious problem of missing component failure modes \cite{faa}[Ch.9]. +\fmodegloss %, or modelling at %a too high level of failure mode abstraction. FTA was invented for use on the minuteman nuclear defence missile @@ -336,7 +337,7 @@ a prioritised `to~do~list', with higher $RPN$ values being the most urgent. \item Complex component interaction effects can be missed. \item No possibility to model base component level double failure modes. \end{itemize} - +\fmodegloss \paragraph{Note.} FMEA is sometimes used in its literal sense, that is to say Failure Mode Effects analysis, simply looking at a systems' internal failure modes and determining what may happen as a result. @@ -400,6 +401,7 @@ Failure Modes, Effects, and Diagnostic Analysis (FMEDA) is a process that takes all the components in a system, and using the failure modes of those components, the investigating engineer ties them to possible SYSTEM level events/failure modes. +\fmodegloss % This technique evaluates a product's statistical level of safety @@ -616,6 +618,7 @@ FIT/PFD and SFF and diagnostic coverage figures.}. \subsubsection{FMEDA and failure outcome prediction accuracy.} FMEDA suffers from the same problems of lack of component failure mode outcome prediction accuracy, as FMEA in section \ref{pfmea}. +\fmodegloss % This is because the analyst has to decide how particular components failing will impact on the SYSTEM or top level. This involves a `leap of faith'. For instance, a resistor failing in a sensor circuit @@ -691,6 +694,7 @@ to smaller and smaller functional groupings \cite{maikowski}. In order to ensure that all component failure modes have been covered the methodology will have to work from the bottom-up and start with the component failure modes. +\fmodegloss % \paragraph{Natural Fault Finding is top down.} The traditional fault finding, or natural fault finding diff --git a/introduction/introduction.tex b/introduction/introduction.tex index fcedbe3..bdf9bfb 100644 --- a/introduction/introduction.tex +++ b/introduction/introduction.tex @@ -273,7 +273,7 @@ This is the probablistic approach and is embodied in the European Standard EN61508 \cite{en61508} (international standard IOC1508). \glossary{name={deterministic},description={Deterministic in the context of failure mode analysis, traces the causes of SYSTEM level events to base level component failure modes}} \glossary{name={probablistic},description={Probablistic in the context of failure mode analysis, traces the probability of base level failure modes causing of SYSTEM level events/failure modes}} - +\fmodegloss \paragraph{Deterministic safety Measures} The second philosophy, applied to application specific standards, is to investigate components for sub-systems in the critical safety path and to look at component failure modes @@ -352,6 +352,7 @@ components. % The `functional group', after analysis, has its own set of derived failure modes. +\fmodegloss % The number of derived failure modes will be less than or equal to the sum of the failure modes of all its components. @@ -476,6 +477,7 @@ This circuit would typically be used to amplify a thermocouple, which typically fails by going open circuit. It {\em does} detect several other failure modes of this circuit and a full analysis is given in appendix \ref{mvamp}. +\fmodegloss % Note C14 shorting is potentially v dangerous could lead to a high output by the opamp being seen as a % low temperature. diff --git a/pt100/pt100.tex b/pt100/pt100.tex index e96bcda..0a020a6 100644 --- a/pt100/pt100.tex +++ b/pt100/pt100.tex @@ -139,7 +139,7 @@ The worst case for this type of analysis would be a fault that we cannot detect. Where this occurs a circuit re-design is probably the only sensible course of action. - +\fmodegloss \subsection{Single Fault FMEA Analysis \\ of PT100 Four wire circuit} @@ -260,6 +260,9 @@ it. The test cases here deal with single faults only and are thus enclosed by one contour each. +\fmodegloss + + \begin{figure}[h] \centering \includegraphics[width=400pt,bb=0 0 518 365,keepaspectratio=true]{./pt100/pt100_tc.jpg} @@ -429,6 +432,7 @@ and values assigned to its co-efficients are described in table \ref{tab:resisto \glossary{name={FIT}, description={Failure in Time (FIT). The number of times a particular failure is expected to occur in a $10^{9}$ hour time period.}} +\fmodegloss \begin{equation} % fixed comp resistor{\lambda}_p = {\lambda}_{b}{\pi}_{R}{\pi}_Q{\pi}_E @@ -617,6 +621,7 @@ TC 18: & $R_2$ SHORT $R_3$ SHORT & low & low & Both out of Rang \subsection{Verifying complete coverage for a \\ cardinality constrained powerset of 2} +\fmodegloss It is important to check that we have covered all possible double fault combinations. diff --git a/style.tex b/style.tex index 9d8e513..cd64865 100644 --- a/style.tex +++ b/style.tex @@ -83,6 +83,9 @@ \newcommand{\pic}{\em pair-wise~intersection~chain} \newcommand{\wrt}{\em with~respect~to} \newcommand{\fmmdgloss}{\glossary{name={FMMD},description={Failure Mode Modular De-Composition, a bottom-up methodolgy for incrementally building failure mode models, using a procedure taking functioal groups of components and creating derived components representing them, and in turn using the derived components to crate higher level functional groups, and so on, that are used to build a failure mode model of a SYSTEM}}} +\newcommand{\fmodegloss}{\glossary{name={failure mode},description={The way in which a failure occurs. A component or sub-system may fail in a number of ways, and each of these is a +failure mode of the component or sub-system}}} + %----- Display example text (#1) in typewriter font diff --git a/symptom_ex_process/topbot.tex b/symptom_ex_process/topbot.tex index 70a9759..d962186 100644 --- a/symptom_ex_process/topbot.tex +++ b/symptom_ex_process/topbot.tex @@ -211,7 +211,7 @@ Base Component & Any bought in component, or \\ \end{table} - +\fmodegloss \glossary{name={system}, description={A product designed to work as a coherent entity}} \glossary{name={sub-system}, description={A part of a system, sub-systems may contain sub-systems and so-on}}