From 8cb5124c28742a6309eeba4dab370b20dcb9c4b0 Mon Sep 17 00:00:00 2001 From: Robin Clark Date: Wed, 26 Dec 2012 14:31:24 +0000 Subject: [PATCH] More intro --- mybib.bib | 36 +++++- submission_thesis/CH1_introduction/copy.tex | 131 ++++++++++++++++---- 2 files changed, 142 insertions(+), 25 deletions(-) diff --git a/mybib.bib b/mybib.bib index fa3e5ff..90d56b3 100644 --- a/mybib.bib +++ b/mybib.bib @@ -290,6 +290,30 @@ Database } + +@article{syssafe2012, + title = "Applying Failure Mode Modular de-composition (FMMD) across the Software/Hardware Interface", + journal = "7th IET International Conference on System Safety 2012", + volume = "", + number = "", + pages = "", + year = "2012", + note = "", + issn = "", + doi = "", + url = "", + author = "Clark, R and Fish, A and Garrett, C and Howse, J", + keywords = "Failsafe", + keywords = "Software", + keywords = "FMEA", + keywords = "FMEDA", + keywords = "FMECA", + keywords = "fault", + keywords = "double-fault", + keywords = "single-fault", + keywords = "fault-tolerance" +} + @ARTICLE{ontfmea, AUTHOR = "Lars Dittman et all", TITLE = "FMEA using Ontologies", @@ -433,6 +457,16 @@ year = {2012}, YEAR = "2002" } +@ +@BOOK{usefulinfoengineers, + AUTHOR = "William Fairbairn", + TITLE = "Useful Information for Engineers +being a series of lectures delivered to the working engineers of Yorkshire and Lancashire : +together with a series of appendices, containing the results of experimental inquiries into the +strength of materials, the causes of boiler explosions", + PUBLISHER = "Longman", + YEAR = "1864" +} @BOOK{opmanage, AUTHOR = "Roger Schroeder", TITLE = "Operations Management: Contemporary Concepts and Cases ISBN: 978-0073403380", @@ -823,7 +857,7 @@ OPTissn = {}, } @Book{aoe, - title = {The Art of Electronics}, + title = {The Art of Electronics, 2nd Edition}, publisher = {Cambridge}, year = {1989}, author = {Paul Horowitz, Winfield Hill}, diff --git a/submission_thesis/CH1_introduction/copy.tex b/submission_thesis/CH1_introduction/copy.tex index 3e0456f..7276a68 100644 --- a/submission_thesis/CH1_introduction/copy.tex +++ b/submission_thesis/CH1_introduction/copy.tex @@ -1,14 +1,47 @@ \paragraph{Abstract}{ +Increasingly we rely on automation in everyday life. +Many of the automated systems have the potential to cause harm or even death, should they fail. +Safety assessment and certification is now required of +almost all potentially dangerous equipment. +% +As part of the assessment/certification process, we typically apply +a battery of tests; examining features such as resistance to extremes of environment, electro magnetic compatibility (EMC), +endurance and static testing. +% +Static testing is at the theoretical, or design level, and involves +looking a failure scenarios and trying to predict how systems would react. +% +This thesis deals with one area of static testing, that of Failure Mode Effects Analysis (FMEA), a commonly +used technique that is legally mandatory for a wide range of equipment. + The ability to assess the safety of man made equipment has been a concern -since the dawn of the industrial age~\cite{indacc01}~\cite{steamboilers}. +since the dawn of the industrial age~\cite{indacc01,usefulinfoengineers,steamboilers}. The philosophy behind safety measure has progressed with time, and by world war two~\cite{boffin} we begin to see concepts such as `no single component failure should cause -a dangerous system failure' emerging. +a dangerous system failure' emerging. Concepts such as these allow us to apply +objective criteria to safety assessment. We can extend the `no~single~failure' concept +to double or even multiple failures not being allowed to cause dangerous states. +% The concept of a double failure causing a dangerous condition being unacceptable, -can be found in the legally binding European standard EN298~\cite{en298}. +can be found in the legally binding European standard EN298 which became +a legal requirement in 2006~\cite{en298}. More sophisticated statistically based standards, i.e EN61508~\cite{en61508} and variants thereof, -governing failure conditions and determining risk levels associated with systems. +are based on statistical thresholds for the frequency of dangerous failures. +We could state, for instance, that we can tolerate an `acceptable' maximum number of +dangerous failure per billion hours of operation. +We can then broadly separate these ratings failure rates into safety integrity levels (SIL). +So for a maximum of 10 failures per billion hours of operation we assign a SIL level of 4, +for 100 a sil level of 3 etc. +If we can determine a SIL rating +we can match it against the risk. +The more dangerous the consequences of failure +the higher SIL rating we can demand for it. +A band-saw with one operative may require a SIL rating of 1, +a nuclear power-station, with far greater consequences on dangerous failure +may require a SIL rating of 4. +SIL ratings give us another objective yardstick to measure system safety. +%governing failure conditions and determining risk levels associated with systems. All of these risk assessment techniques are based on variations on the theme of Failure Mode Effect Analysis (FMEA), which has its roots in the 1940's mass production industry @@ -31,10 +64,13 @@ firstly looking at electronic circuits and then at electronic/software hybrid sy \section{Introduction} The motivation for this study came form two sources, one academic and the other -practical. I had recently completed an -Msc and my project was to create an Euler/Spider Diagram editor in Java. +practical. +\paragraph{MSc Project: Euler/Spider diagram Editor.} +I had recently completed an +MSc and my project was to create an Euler/Spider~Diagram~\cite{howse:spider} editor in Java. This editor allowed the user to draw Euler/Spider diagrams, and could then -represent these as abstract---or mathematical---definitions. +represent these as abstract---i.e. mathematical---definitions. +\paragraph{European Safety Requirements increase in scope and complexity.} At work, writing embedded `C' and assembly language code for safety critical industrial burners, we were faced with a new and daunting requirement. Conformance to the latest European standard, EN298. It appeared to ask for the impossible, @@ -48,7 +84,18 @@ documented and approved using failure mode effects analysis (FMEA). This new req effectively meant that any all combinations of component failures were now required to be analysed. This, from a state explosion problem alone, meant that it was going to be virtually impossible to perform. +FMEA had a deficiency of repeated work, as each component failure is typically represented +by one line or entry in a spreadsheet~\cite{bfmea}, analysis on repeated section of +circuitry (for instance repeated 4-20mA outputs on a PCB), meant that +analysis of identical circuitry was performed many times. +A desirable feature of a new methodology would be to be able to re-use +analysis for identical repeated modules. The development of this new methodology +was presented to the IET System safety conference in 2011~\cite{syssafe2011}. +FMEA, currently cannot integrate software into its failure mode models. +A modular variant of FMEA can use the existing structure of functional software, in conjunction +with contract programming, to model software~\cite{syssafe2012}. % +\paragraph{Modularising FMEA and augmenting this with concepts from Euler/Spider Diagrams} Following the concept of de-composing a problem, and thus simplifying the state explosion---using the thinking behind the fast Fourier transform (FFT)~\cite{fpodsadsp}[Ch.8], which takes a complex intermeshed series of real and imaginary number calculations and by de-composing them simplifies the problem. @@ -58,32 +105,68 @@ Once these first modules were analysed, I now call them {\fgs}, I could determin Using the symptoms of failure, I could now treat these modules as components, now called {\dcs}, and use them to build higher level modules. I could apply double simultaneous failure mode checking, because the number of components in each module/{\fg} was quite small---thus avoiding state explosion problems, but I could apply -double checking all the way up the hierarchy. In fact this meant, as a by-product that many multiple as well as double -failures would be analysed. +double checking all the way up the hierarchy. +In fact this means, as a by-product that many multiple as well as double +failures would be analysed, but because failure modes are traceable from the base components to the top level---or system---failure modes +and these are held in a data structure, we can apply automated methods to search all cardinalities of multiple failure modes +within the model. +% +Because, Euler/Spider Diagrams +could be used to model failure modes in components +it was thought that a diagrammatic notation would +be easier to demonstrate than using formal logic. +% - -Euler/Spider Diagrams -could be used to model failure modes in components. -Contours could represent failure modes, and the spider diagram +For an FMEA Spider diagram, contours represent failure modes, and the spider diagram `existential~points' instances of failure modes. +Overlapping contours could represent multiple failure modes. By drawing a spider collecting existential points, a common failure symptom could be determined and from this a new diagram generated automatically, to represent the {\dc}. +% Each spider represented a derived failure mode. -These concepts were presented at the ``Euler~2004''~\cite{Clark200519} conference at Brighton University. +The act of collecting common symptoms by drawing spiders +meant that the analyst was forced to associate one component failure mode with one symptom/derived~failure~mode of failure. +% +These concepts were presented at the ``Euler~2004''~\cite{Clark200519} conference held at Brighton University. +This brought together concepts for modularising FMEA and the formal visual notations from Spider diagrams. +Euler diagrams have been used later in the thesis to describe the containment relationships +of derived components building hierarchical analysis models with the modularised +variant of FMEA that this thesis proposes and defends. ---- 2005 paper --- need for static analysis because of -high reliability of modern safety critical systems. +\paragraph{Objectives of the thesis}. +The primary objective of the work performed for this thesis is to propose a modularised variant of +FMEA that solves the problems of: +\begin{itemize} + \item State Explosion, + \item Multiple failure mode modelling, + \item Re-usability of pre-analysed modules, + \item Inclusion of software in failure mode modelling. +\end{itemize} -\section{Practical Experience: Safety Critical Product Approvals} -FMEA performed on selected areas perceived as critical -by test house. -Blanket measures, RAM ROM checks, EMC, electrical and environmental stress testing +Chapter~\ref{chap2} examines the current state of FMEA based methodologies, Chapter~\ref{chap3} +examines the benifits and drawbacks of these these methodologies +and proposes a detailed wish list for an ideal FMEA technique. +Chapter~\ref{chap4} proposes Failure Mode Modular de-composition (FMMD)---a modularised variant +of FMEA designed to address the points in the detailed wish list. +Chapter~\ref{chap5} provides worked examples usin g common electronic circuits. +Chapter~\ref{chap6} gives two examples of integgrated software and electronic systems anyalysed using FMMD. +Metrics and evaluation, along with an example showing double simultaneous failure analysis +are dealt with in Chapter~\ref{chap7} -\subsection{Practical limitations of testing for certification vs. rigorous approach} -State explosion problem considering a failure mode of a given component against -all other components in the system i.e. an exponential ($2^N$) order of processing resource rather than a polynomial i.e. $N^2$. -Impossible to perform double simultaneous failure analysis (as demanded by EN298~\cite{en298}). +% \section{Case Study: Safety Critical Product Approval changes for EN298:2003} +% +% FMEA performed on selected areas perceived as critical +% by test house. +% Blanket measures, RAM ROM checks, EMC, electrical and environmental stress testing +% +% \subsection{Practical limitations of testing for certification vs. rigorous approach} +% +% State explosion problem considering a failure mode of a given component against +% all other components in the system i.e. an exponential ($2^N$) order of processing resource +% rather than a polynomial i.e. $N^2$. +% +% Impossible to perform double simultaneous failure analysis (as demanded by EN298~\cite{en298}).