From b6a7d4893b73e119890e7f88fead98cdfbeee159 Mon Sep 17 00:00:00 2001 From: Robin Clark Date: Fri, 30 Sep 2011 08:52:00 +0100 Subject: [PATCH 1/4] Added more FMEDA Need to put mill-volt amp in as a block diagram Then need to put the SYSTEM SAFETY presentation in at the end --- presentations/fmea/fmea_pres.tex | 60 ++++++++++++++++++++++++++++++-- 1 file changed, 58 insertions(+), 2 deletions(-) diff --git a/presentations/fmea/fmea_pres.tex b/presentations/fmea/fmea_pres.tex index 767447d..de28066 100644 --- a/presentations/fmea/fmea_pres.tex +++ b/presentations/fmea/fmea_pres.tex @@ -333,8 +333,63 @@ FMEDA is the methodology behind statistical (safety integrity level) type standards (EN61508/IOC5108). It provides a statistical overall level of safety and allows diagnostic mitigation for self checking etc. +It provides guidelines for the design and architecture +of computer/software systems for the four levels of +safety Integrity. +For Hardware + +FMEDA does force the user to consider all components in a system +by requiring that a MTTF value is assigned. +This MTTF may be statistically mitigated (improved) +if it can be shown that selfchecking will detect failure modes. \end{frame} +\begin{frame} +Failure modes are classified as Safe or Dangerous according +to the putative system level failure they will cause. +The Failure modes are also classified as Detected or +Undetected. +This gives us four level failure mode classifications: +Safe-Detected (SD), Safe-Undetected (SU), Dangerous-Detected (DD) or Dangerous-Undetected (DU), +and the probablistic failure rate of each classification +is represented by lambda variables +(i.e. $\lambda_{SD}$, $\lambda_{SU}$, $\lambda_{DD}$, $\lambda_{DU}$). +\end{frame} +\begin{frame} +\textbf{Diagnostic Coverage.} +The diagnostic coverage is simply the ratio +of the dangerous detected probabilities +against the probability of all dangerous failures, +and is normally expressed as a percentage. $\Sigma\lambda_{DD}$ represents +the percentage of dangerous detected base component failure modes, and +$\Sigma\lambda_D$ the total number of dangerous base component failure modes. + +$$ DiagnosticCoverage = \Sigma\lambda_{DD} / \Sigma\lambda_D $$ +\end{frame} + + +\begin{frame} +The diagnostic coverage for safe failures, where $\Sigma\lambda_{SD}$ represents the percentage of +safe detected base component failure modes, +and $\Sigma\lambda_S$ the total number of safe base component failure modes, +is given as + +$$ SF = \frac{\Sigma\lambda_{SD}}{\Sigma\lambda_S} $$ + + +\textbf{Safe Failure Fraction.} +A key concept in FMEDA is Safe Failure Fraction (SFF). +This is the ratio of safe and dangerous detected failures +against all safe and dangerous failure probabilities. +Again this is usually expressed as a percentage. + +$$ SFF = \big( \Sigma\lambda_S + \Sigma\lambda_{DD} \big) / \big( \Sigma\lambda_S + \Sigma\lambda_D \big) $$ + +\end{frame} + +\begin{frame} + SIL Levels are how they are calculated +\end{frame} \section{FMEA - General Criticism} \begin{frame} @@ -347,8 +402,9 @@ and allows diagnostic mitigation for self checking etc. \pause \item FMEA type methodologies were designed for simple electro-mechanical systems of the 1940's to 1960's. \end{itemize} -FMEDA is an extension of FMEA, in that it will give higher ratings -for self checking. It +FMEDA is a modern extension of FMEA, in that it will allow for +self checking features, and provides detailed recommendations for computer/software architecture, +but \end{frame} From 8ed37030ca3f85835d4d91dc8d78408f2bf2f167 Mon Sep 17 00:00:00 2001 From: Robin Clark Date: Fri, 30 Sep 2011 11:10:30 +0100 Subject: [PATCH 2/4] moved approvals FMEA to the end --- presentations/fmea/fmea_pres.tex | 146 ++++++++++++++++++------------- 1 file changed, 86 insertions(+), 60 deletions(-) diff --git a/presentations/fmea/fmea_pres.tex b/presentations/fmea/fmea_pres.tex index de28066..7c6aa5f 100644 --- a/presentations/fmea/fmea_pres.tex +++ b/presentations/fmea/fmea_pres.tex @@ -131,41 +131,6 @@ double failure scenarios (for burner lock-out scenarios). \end{frame} -\section{FMEA used for Saftey Critical Aprovals} -\begin{frame} -\frametitle{Safety Critical Approvals FMEA} -Experts from Approval House and Equipement Manufacturer -discuss selected component failure modes -judged to be in critical sections of the product. - - -\begin{figure}[h] - \centering - \includegraphics[width=100pt,keepaspectratio=true]{./tech_meeting.png} - % tech_meeting.png: 350x299 pixel, 300dpi, 2.97x2.53 cm, bb=0 0 84 72 - \caption{FMEA Meeting} - \label{fig:tech_meeting} -\end{figure} -\end{frame} - -\begin{frame} -\frametitle{Safety Critical Approvals FMEA} - -\begin{figure}[h] - \centering - \includegraphics[width=70pt,keepaspectratio=true]{./tech_meeting.png} - % tech_meeting.png: 350x299 pixel, 300dpi, 2.97x2.53 cm, bb=0 0 84 72 - \caption{FMEA Meeting} - \label{fig:tech_meeting} -\end{figure} - -\begin{itemize} - \pause \item Impossible to look at all component failures let alone apply FMEA rigorously. - \pause \item In practise, failure scenarios for critical sections are contested, and either justified or extra safety measures implemented. - \pause \item Meeting notes or minutes only. -\end{itemize} - -\end{frame} \section{PFMEA - Production FMEA : 1940's to present} @@ -345,6 +310,7 @@ if it can be shown that selfchecking will detect failure modes. \end{frame} \begin{frame} +\frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} Failure modes are classified as Safe or Dangerous according to the putative system level failure they will cause. The Failure modes are also classified as Detected or @@ -356,6 +322,7 @@ is represented by lambda variables (i.e. $\lambda_{SD}$, $\lambda_{SU}$, $\lambda_{DD}$, $\lambda_{DU}$). \end{frame} \begin{frame} +\frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} \textbf{Diagnostic Coverage.} The diagnostic coverage is simply the ratio of the dangerous detected probabilities @@ -369,6 +336,7 @@ $$ DiagnosticCoverage = \Sigma\lambda_{DD} / \Sigma\lambda_D $$ \begin{frame} +\frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} The diagnostic coverage for safe failures, where $\Sigma\lambda_{SD}$ represents the percentage of safe detected base component failure modes, and $\Sigma\lambda_S$ the total number of safe base component failure modes, @@ -388,9 +356,49 @@ $$ SFF = \big( \Sigma\lambda_S + \Sigma\lambda_{DD} \big) / \big( \Sigma\lambda_ \end{frame} \begin{frame} +\frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} SIL Levels are how they are calculated \end{frame} + + +\section{FMEA used for Safety Critical Approvals} + +\begin{frame} +\frametitle{Safety Critical Approvals FMEA} +Experts from Approval House and Equipment Manufacturer +discuss selected component failure modes +judged to be in critical sections of the product. + + +\begin{figure}[h] + \centering + \includegraphics[width=100pt,keepaspectratio=true]{./tech_meeting.png} + % tech_meeting.png: 350x299 pixel, 300dpi, 2.97x2.53 cm, bb=0 0 84 72 + \caption{FMEA Meeting} + \label{fig:tech_meeting} +\end{figure} +\end{frame} + +\begin{frame} +\frametitle{Safety Critical Approvals FMEA} + +\begin{figure}[h] + \centering + \includegraphics[width=70pt,keepaspectratio=true]{./tech_meeting.png} + % tech_meeting.png: 350x299 pixel, 300dpi, 2.97x2.53 cm, bb=0 0 84 72 + \caption{FMEA Meeting} + \label{fig:tech_meeting} +\end{figure} + +\begin{itemize} + \pause \item Impossible to look at all component failures let alone apply FMEA rigorously. + \pause \item In practise, failure scenarios for critical sections are contested, and either justified or extra safety measures implemented. + \pause \item Meeting notes or minutes only. +\end{itemize} + +\end{frame} + \section{FMEA - General Criticism} \begin{frame} \frametitle{FMEA - General Criticism} @@ -402,42 +410,60 @@ $$ SFF = \big( \Sigma\lambda_S + \Sigma\lambda_{DD} \big) / \big( \Sigma\lambda_ \pause \item FMEA type methodologies were designed for simple electro-mechanical systems of the 1940's to 1960's. \end{itemize} -FMEDA is a modern extension of FMEA, in that it will allow for -self checking features, and provides detailed recommendations for computer/software architecture, -but +%FMEDA is a modern extension of FMEA, in that it will allow for +%self checking features, and provides detailed recommendations for computer/software architecture, +%but \end{frame} +\begin{frame} +\frametitle{FMEA - Better Metodology - Wish List} +\begin{itemize} + + \pause \item State explosion + \pause \item Rigorous + \pause \item Reasoning Traceable + \pause \item re-useable + \pause \item +\end{itemize} + +%FMEDA is a modern extension of FMEA, in that it will allow for +%self checking features, and provides detailed recommendations for computer/software architecture, +%but + +\end{frame} \section{Failure Mode Modular De-Composition} -\subsection{FMEA and complexity of each failure scenario analysis} \begin{frame} -Consider the FMEA type methodologies -where we look at all the failure modes in a system, and then -see how they can affect all other components within it, -to determine its system level symptom or failure mode. -We need to look at a large number of failure scenarios -to do this completely (all failure modes against all components). -This is represented in equation~\ref{eqn:fmea_state_exp}, -where $N$ is the total number of components in the system, and -$cfm$ is the number of failure modes per component. - -\begin{equation} - \label{eqn:fmea_state_exp} - N.(N-1).cfm % \\ - %(N^2 - N).cfm -\end{equation} +% Consider the FMEA type methodologies +% where we look at all the failure modes in a system, and then +% see how they can affect all other components within it, +% to determine its system level symptom or failure mode. +% We need to look at a large number of failure scenarios +% to do this completely (all failure modes against all components). +% This is represented in equation~\ref{eqn:fmea_state_exp}, +% where $N$ is the total number of components in the system, and +% $cfm$ is the number of failure modes per component. +% +% \begin{equation} +% \label{eqn:fmea_state_exp} +% N.(N-1).cfm % \\ +% %(N^2 - N).cfm +% \end{equation} The FMMD methodology breaks the analysis down into small stages, -by making the analyst choose functional groups, and then when analysed the groups -are treated as components to be used for a higher stage. -This is designed to address the state explosion (where $O$ is order +by making the analyst choose functional groups of components, which are then when analysed. +When analysed, we will have a set of symptoms of failure for the functional group. +We can then create a derived~component, +to represent the functional group. +We can use derived components to form `higher~level' functional groups. +This addresses the state explosion (where $O$ is order of complexity) $O=N^2$ inherent in equation~\ref{eqn:fmea_state_exp}. \end{frame} - +\begin{frame} We can view the functional groups in FMMD as forming a hierarchy. If for the sake of example we consider each functional group to be three components, figure~\ref{fig:three_tree} shows @@ -451,7 +477,7 @@ how the levels work and converge to a top or system level. \label{fig:three_tree} \end{figure} -\clearpage +\end{frame} We can represent the number of failure scenarios to check in an FMMD hierarchy with equation~\ref{eqn:anscen}. @@ -498,7 +524,7 @@ group is the same for equation~\ref{eqn:fmea_state_exp22} and equation~\ref{eqn:anscen}. \clearpage -\section{Example} +%\section{Example} To see the effects of reducing `state~explosion' we need to look at a larger system. Let us take a system with 3 levels and apply these formulae. From b2eb249c95a6704a396f3dd540c597eb56bb3b4d Mon Sep 17 00:00:00 2001 From: Robin Clark Date: Fri, 30 Sep 2011 11:23:13 +0100 Subject: [PATCH 3/4] hieracrhy of FMMD being described --- presentations/fmea/fmea_pres.tex | 6 ++++-- presentations/fmea/three_tree.dia | Bin 0 -> 2117 bytes presentations/fmea/three_tree.png | Bin 0 -> 13487 bytes 3 files changed, 4 insertions(+), 2 deletions(-) create mode 100644 presentations/fmea/three_tree.dia create mode 100644 presentations/fmea/three_tree.png diff --git a/presentations/fmea/fmea_pres.tex b/presentations/fmea/fmea_pres.tex index 7c6aa5f..88ccee8 100644 --- a/presentations/fmea/fmea_pres.tex +++ b/presentations/fmea/fmea_pres.tex @@ -454,11 +454,13 @@ judged to be in critical sections of the product. The FMMD methodology breaks the analysis down into small stages, -by making the analyst choose functional groups of components, which are then when analysed. +by making the analyst choose functional groups of components, to which FMEA is applied. When analysed, we will have a set of symptoms of failure for the functional group. We can then create a derived~component, to represent the functional group. We can use derived components to form `higher~level' functional groups. +This creates an analysis hierarchy. + This addresses the state explosion (where $O$ is order of complexity) $O=N^2$ inherent in equation~\ref{eqn:fmea_state_exp}. \end{frame} @@ -466,7 +468,7 @@ of complexity) $O=N^2$ inherent in equation~\ref{eqn:fmea_state_exp}. \begin{frame} We can view the functional groups in FMMD as forming a hierarchy. If for the sake of example we consider each functional group to -be three components, figure~\ref{fig:three_tree} shows +be three components, the figure below shows how the levels work and converge to a top or system level. \begin{figure} diff --git a/presentations/fmea/three_tree.dia b/presentations/fmea/three_tree.dia new file mode 100644 index 0000000000000000000000000000000000000000..226f2db49212ffdc3e01ef9d4363fdeabd499ce7 GIT binary patch literal 2117 zcmV-L2)g$liwFP!000021MQqmbK^D=hVSz$RGO;-p&Q@B*s0`@+QZiFA<5ZANgSC8 zMY<%~9$)siF91rhC6Tr)2y&Q6RWoJF5E>0Ve9`Cz`TY;y7RBHpTdwk|yczvz+-UgnegIvbSfBD)$+(&-=bWp!W9hE1z= zyJ=Na%fUlhTn#^e^{?T0-OYHbpI7?6OXt~SnWcYpcTMffm}9!W%a*&{F7B#TZkyCk zcY94b`f>liXtQp$vW?35_2(b?=VnOjH=g@y8)&DIdXX;YdAV=L&P~xw1QLyib~1#~ zhAOULGbisiH#x7l;=JaT=QWqFZtkjOy-f3Z-{hpKiYzS~tM&3eJKoM}nidwZ*W3#5 z;%i>l)f?mgnii`=9BAJD^J;tVl{;VNv)3=&tri`1uj^iq!i z);9XQtWVbc(`mZj{dT;1KYu)shNid99o!tHov`?lWOvNHm%pr{!*vqEM3k9 z-wl4Mz73ya5F3Hyv#a5M>Govpx@SAHI=DAmchxgenouzUVs@usUqHGHOeVYiFRce@ zIWMw}4QoJ)1d;F&Crlh?D=V_a&9qvU`|-i)9P&oIknB6P5fSSG-Fm42Ten$0zpcBC z**V)b#*Z_$x~(2>TEfP+*TnYgcl-?N(ey$ny@pUJMv72~h_5vQVkC)?2{6L#&xUXr zli^UeE)bs)VmyHaGi~`&7*&G_W7ddNPKFh;41InmCk$HS-vl_&r9=2-HdHwqzd!^vFJJoa!!HjHB(!IXMU5l0$5$j4U4@=t zE#k%zL0%n#uuIy!WH=}=It1aDFDCnl@W1miYhhS~GOUOOCQT!eG-fcNh~kV&8$&Ry z1xpMuRAPggq(|z?v?|M+tekm|j`Fkh0$@U-3)qE$BWWq`7t_1l@wDY+UhC9(XD88q z^C0oa5BjGRcpn=e;K4T%wm z;o1oyHCl?qT2{!Fv&_Y@`}%_+?)0;zDH000zZmoWVGO}lI%EV~x`2zg2!nz~g%L1u zMy1A)U*k2#M!3brmR2qlHcj@LqV5a5=K`>!%obc{14g9u`}<=z(TBwW)(kXeAOT4P zcSIlfpX_-EXo)YEEyOuXD8La+6*CE=gi7j9-+(wa@qBpVq07(xrfy(VNq?yw8~%J? z>db`HFvJJt&VoyEOxU;;eEbS3W+je+Rb=Fr4rQnoi8E}#CuNZ<9vR~1XR%9Zo6Ofdb{Me+dT>uvMcUvs1%U z)a1B*x$jpVeOmj_x*RfO77sLv`YJOwO8J{E(ZoK$-sxv+Q`AEGd;jUN3B3m4Hppd)!-_fwxM<+Y|Y=5)_<>)ZxTEjo-2zzXd zf6cztFEEA;#=*5XM)U|t)Qz6It<&xAP$YJr$G8&KqCPe}uH8($@i3pAHeGR|fBM;0 zyPXH6(JvhjN_*w$LS2uls>-^}lzV^hHC^PzlO0i7u7-nE{j|oi`RKp0;vuW^Y5Ee# z_m5yN{B8}w!7f%>yZpRDqYZ}H+-C0}{*E!T{kWx9p23x^OgCElF1@Sx-cG}%dmktG2Q(aa)<{sTGmu#&;#%qu!ybl@#7Y&N7K|AbS z6sV616kZ1>K5fUMhCD|Qj1*kZKL;6;u4s7Ap@TR0`nkrNYBkN&hmg^P}m vC~o|6i2YC`b5W$&+q5xvv@cuc0z)FxKUA*cLIo{Q zJMYf^jU=J7##x8HJc7SW(9nBN=k;3Pq zLyM)(5@U@4SBG3{Y)8+txPNIBX`N3Tm>YE}>TW%L;AzP=EP}A9;AKnxNsx~JDN2xB z4SoLnyXd1!r_Y`>WZpuE3EP&_xr24j)`uRp+q^vN=?P|ejLGcli$$C36M2(-28D_w zHkkmuT+8FH58Y|s z9d$46bIVoa2Rxc25Hf7tg{@wOhVmE`<|if9w6+SLB0p+dTeFjrtV*67I)424UN-W^ zmG$&UtC2_~4UJ|W7B~7MN7h<&?-tCr=>GTLf9WRGpAr+F`TE|Vr^Z_)H#Yb}+*Zeh ziRKTC{Z~&PJNCPoZRl@~TJOd%AvVT=Mqz z-X~G*x-?w>Rx>bW-$A?-y2Y+@2Yv?iP7=%8+Ftp-5qIsFYV7nWaGDRX;lV3}EXKof z!gssxEZv@vnouV{Q_(j`9Eq~;J{CtoNhPo*uozoVP@pHZ1uvy6EC&3-ec|JuK7E>* zpVu#R5uqOM%(ba}!5bxN>$Eg=^Ch4DtHEt%hABM)g%sG&%q1EJcL|U+=Mv zGlaZCcFACJ5U_4}!cP8kmnu7Xak3ux1h#N1tsMDTniyH~?gSB}|9|;WkG;8Hzk2)l zXliPvQ*9;G-P)R}RV7LxDaL+ar?2emP1pN9TLNNZf6ok5zU0+y`JyZA9ZVqTY~z+A zuu2WpMn|79ynN+K{mT59zrVk}zW!N$el4G^1T(rs_AO=GvI9b*qN+uAo*f(ur5_W3=hxn>TN$sHhUpZY2n8m!|Ph6v%IjuVO6x-ajy~KJ|V7 z@87>qUC(EYi_dn0sp<2_3p+Jd^R|2;ie)t`%eRH8ws9d7Cr3K4&K!E8z4Z)ftA|j%r z4e+A23m>nSsPp1>Z&TEC@O--PHaM`yn;eOe*TWV^aq%jK7anq zL_-r27M8%uTdtpHcRVg6gr?=#%T zU0t~O-8+@)_(dNo=Es+ADk=HDdv{`tr+WTxdwPNMqPLgVAzIo4!MVB16=B>jd9>pa z5=ulF37m(KAH2_lgMW{YN4H-&UO?YoiQA{Vsf86d2;^zd2cG_@K>)synlZf+x7bO z$Ff5-Ty~RojRJy#h|I>uM#EdTeg-h>UcE|7Pv7=g^OUA$>#yv)>B^J@`7P2k#Su8; 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u>xO|TTok9K2;mWwguHr;g#KISs{7UyV|gb%sh>C?f}FH6De2OUNB;+*wl7`) literal 0 HcmV?d00001 From a06d136ee40917308b3410e620defe1981c51339 Mon Sep 17 00:00:00 2001 From: Robin Clark Date: Fri, 30 Sep 2011 13:53:38 +0100 Subject: [PATCH 4/4] more on FMEDA --- presentations/fmea/fmea_pres.tex | 45 +++++++++++++++++++++++++++++--- 1 file changed, 41 insertions(+), 4 deletions(-) diff --git a/presentations/fmea/fmea_pres.tex b/presentations/fmea/fmea_pres.tex index 88ccee8..45d0bfa 100644 --- a/presentations/fmea/fmea_pres.tex +++ b/presentations/fmea/fmea_pres.tex @@ -352,14 +352,53 @@ against all safe and dangerous failure probabilities. Again this is usually expressed as a percentage. $$ SFF = \big( \Sigma\lambda_S + \Sigma\lambda_{DD} \big) / \big( \Sigma\lambda_S + \Sigma\lambda_D \big) $$ +SFF determines how proportionately fail-safe a system is, not how reliable it is ! \end{frame} \begin{frame} \frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} - SIL Levels are how they are calculated +To achieve SIL levels, diagnostic coverage and SFF levels are prescribed along with +hardware architectures and software techniques. +Over all the aim of SIL is classify the safety of a system, +by statistically determining how frequently it can fail dangerously. + + \end{frame} +\begin{frame} +\frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} +{ +\begin{table}[ht] +\caption{FMEA Calculations} % title of Table +%\centering % used for centering table +\begin{tabular}{|| l | l | c | c | l ||} \hline + \textbf{SIL} & \textbf{Low Demand} & \textbf{Continuous Demand} \\ + & Prob of failing on demand & Prob of failure per hour \\ \hline \hline + 4 & $ 10^{-5}$ to $< 10^{-4}$ & $ 10^{-9}$ to $< 10^{-8}$ \\ \hline + 3 & $ 10^{-4}$ to $< 10^{-3}$ & $ 10^{-8}$ to $< 10^{-7}$ \\ \hline + 2 & $ 10^{-3}$ to $< 10^{-2}$ & $ 10^{-7}$ to $< 10^{-6}$ \\ \hline + 1 & $ 10^{-2}$ to $< 10^{-1}$ & $ 10^{-6}$ to $< 10^{-5}$ \\ \hline + +\hline +\end{tabular} +\end{table} +} +Table adapted from EN61508-1:2001 [7.6.2.9 p33] +\end{frame} + +\begin{frame} +\frametitle{ FMEDA - Failure Modes Effects and Diagnostic Analysis} +FMEDA is a modern extension of FMEA, in that it will allow for +self checking features, and provides detailed recommendations for computer/software architecture. +It also has a simple final result, a Safety Integrity Level (SIL) from 1 to 4 (where 4 is safest). + +FMEA can be used as a term simple to mean Failure Mode Effects Analysis, and is +part of product approval for many regulated products in the EU and the USA... + +\end{frame} + + \section{FMEA used for Safety Critical Approvals} @@ -410,9 +449,7 @@ judged to be in critical sections of the product. \pause \item FMEA type methodologies were designed for simple electro-mechanical systems of the 1940's to 1960's. \end{itemize} -%FMEDA is a modern extension of FMEA, in that it will allow for -%self checking features, and provides detailed recommendations for computer/software architecture, -%but +% \end{frame}