diff --git a/logic_diagram/logic_diagram.tex b/logic_diagram/logic_diagram.tex index 8b50753..42d1514 100644 --- a/logic_diagram/logic_diagram.tex +++ b/logic_diagram/logic_diagram.tex @@ -12,7 +12,7 @@ that control the flow of a computer program. This type of diagram can therefore integrate logical models from mechanical, electronic and software domains. Nearly all modern safety critical systems involve these three disiplines. % -It is intended to be used for analysis of automated safety critical systen +It is intended to be used for analysis of automated safety critical systems. Many types of safety critical systems now legally require fault mode effects analysis\cite{FMEA}, but few formal systems exist and wide-spread take-up is @@ -231,12 +231,11 @@ In English: Test points on the concrete diagram pair-wise connected by a `joining line' -A collection of test points connected by joining lines, is an Fuctionally Merged Group, $FMG$ +A collection of test points connected by joining lines, is an Functionally Merged Group, $FMG$ or `test point disjunction'. An $FMG$ has members which are test points. -{may be merged -and create a +{ \definition{ %A spider is a set of test points where, %a test point is a member of a spider where it can trace a path connected by joining lines @@ -256,6 +255,7 @@ A singleton test point can be considered a sequence of one test point and is the % \subsection{Abstract Description of PLD} +%and create a % % An Abstract PLD {\em Propositional logic diagram} consists of contours $C$ defining zones $Z$, test points $T$ (which % are defined by the zone they inhabit) and pair wise connections $W$, which connect test points. @@ -284,11 +284,10 @@ A singleton test point can be considered a sequence of one test point and is the \item A $FMG$ represents the disjunction of all test points that are members of it. \end{itemize} -To obtain the set of propositions from a PLD, each $FMG$ must be processed. For each test case +To obtain the set of propositions from a PLD, each $FMG$ must be traversed +along each joining line. For each test case in the $FMG$ a new section of the equation is disjuctively appended to it. - - Let conjunctive logic equation associated with a test point be determined from the contours that enclose it. i.e. the contours $\mathcal{X}$ from the zone it inhabits. @@ -397,6 +396,7 @@ In the diagram \ref{fig:ld_and} the area of intersection between the contours $a represents the conjunction of those conditions. The point $P$ represents the logic equation $$ P = (a \wedge b) $$ There are no disjunctive joining lines and so this diagram represents one equation only, $ P = (a \wedge b) $. +Note that $P$ is considered to be an $FMG$ with one element, $ (a \wedge b) $ \paragraph{How this would be interpreted in failure analysis} In failure analysis, this could be considered to be a sub-system with two failure states $a$ and $b$. @@ -430,23 +430,43 @@ $$ P = (a) $$ $$ Q = (b) $$ The two test cases are joined by a the line named $R$. -we thus apply disjunction to the test cases. -$$ R = P \vee Q $$ +we thus apply exclusive disjunction to the test cases. +$$ R = P \oplus Q $$ substituting the test cases for their Boolean logic equations gives -$$ R = ((a) \vee (b)) $$. +\begin{equation} +\label{eqn:l_or} + R = ((a) \oplus (b)) +\end{equation} + +\paragraph{Failure Analysis Interpretation} +Equation \ref{eqn:l_or} would be interpretted to mean that +either failure mode a or b occurring, would have the same failure symptom for the circuit/sub-system +under analysis. \clearpage \subsection {Labels and useage} -In diagram \ref{fig:ld_meq} Z and W were labeled but were not necessary for the final expression -of $ R = b \vee c $. The intended use of these diagrams, is that resultant logical conditions be used in a later stage of reasoning. -Test cases joined by disjunction, all become represented in one, resultant equation. -Therefore only test cases not linked by any disjunctive joining lines need be named. +%In diagram \ref{fig:ld_meq} Z and W were labeled but were not necessary for the final expression +%of $ R = b \vee c $. The intended use of these diagrams, is that resultant logical conditions be used in a later stage of reasoning. +%Test cases joined by disjunction, all become represented in one, resultant equation. +%Therefore only test cases not linked by any disjunctive joining lines need be named. +% +%The diagram \ref{fig:ld_meq} can therefore be represented as in diagram \ref{fig:ld_meq2}, with +%two unnamed test cases. + +Diagram \ref{fig:ld_meq} +shows three Functionally Merged groups, Q, R and P. + +Z and W were labeled but this was not necessary for determination of the final expression +of $ R = b \oplus c $. +%The intended use of these diagrams, is that resultant logical conditions be used in a later stage of reasoning. +%Test cases joined by disjunction, all become represented in one, resultant equation. +%Therefore only test cases not linked by any disjunctive joining lines need be named. +%The diagram \ref{fig:ld_meq} can therefore be represented as in diagram \ref{fig:ld_meq2}, with +%two unnamed test cases. -The diagram \ref{fig:ld_meq} can therefore be represented as in diagram \ref{fig:ld_meq2}, with -two unnamed test cases. \begin{figure}[h] \centering @@ -457,7 +477,7 @@ two unnamed test cases. % % \begin{figure}[h+] -% %\centering +% %\centeringeragraph % %\input{millivolt_sensor.tex} % \begin{center} % \includegraphics[width=200pt,bb=0pt 0pt 600pt 600pt]{logic_diagram/ldmeq2.jpg} @@ -470,12 +490,20 @@ two unnamed test cases. \paragraph{How this would be interpreted in failure analysis} -In failure analysis, this could be considered to be a sub-system with two failure states $a$ and $b$. -The proposition $P$ considers the scenario where either failure~mode is active. -Additionally it says that either failure mode $a$ or $b$ being active -will have a resultant effect $R$ on the sub-system. Note that the effect -of $a$ and $b$ both being active is not defined on this diagram. +In failure analysis, this could be considered to be a sub-system with three failure states $a$,$b$ and $c$. +It has three FMG's Q,R and P. Thus there are three ways in which this sub-system can fail. +% \tiny +\vspace{0.3cm} + \begin{tabular}{||c|c|l||} \hline \hline + {\em $FMG$ } & {\em Failure Mode equation } & {\em comments } \\ \hline + Q & $(a)$ & T \\ \hline + P & $(b \oplus c)$ & T \\ \hline + R & $(b \wedge c)$ & F \\ \hline + % T & T & T \\ \hline \hline + \end{tabular} +\vspace{0.3cm} +% \normalsize \clearpage @@ -488,15 +516,22 @@ Repeated contours are allowed in PLD diagrams. Logical contradictions or tautologies can be detected automatically by a software tool which assists in drawing these diagrams. - - \begin{figure}[h] \centering - \includegraphics[bb=0 0 485 206]{logic_diagram/repeated.jpg} - % repeated.jpg: 539x229 pixel, 80dpi, 17.11x7.27 cm, bb=0 0 485 206 - \label{fig:repeat} + \includegraphics[width=400pt,bb=0 0 560 195,keepaspectratio=true]{./repeated.jpg} + % repeated.jpg: 560x195 pixel, 72dpi, 19.76x6.88 cm, bb=0 0 560 195 + \caption{Contours can appear more than once in a PLD} + \label{fig:repeated} \end{figure} +% +% \begin{figure}[h] +% \centering +% \includegraphics[bb=0 0 485 206]{logic_diagram/repeated.jpg} +% % repeated.jpg: 539x229 pixel, 80dpi, 17.11x7.27 cm, bb=0 0 485 206 +% \label{fig:repeat} +% \end{figure} + % \begin{figure}[h] % \centering % \includegraphics[bb=0 0 486 206]{./repeated.jpg} @@ -513,19 +548,22 @@ $$ Q = (a) \wedge (c) $$ The two test cases are joined by a the line named $R1$. we thus apply disjunction to the test cases. -$$ R1 = P \vee Q $$ -$$ R1 = b \vee ( a \wedge c ) $$. +$$ R1 = P \oplus Q $$ +$$ R1 = b \oplus ( a \wedge c ) $$. $R2$ joins two other test cases -$$R2 = a \vee c $$ +$$R2 = a \oplus c $$ The test~case residing in the intersection of countours $B$ and $A$ represents the logic equation $R3 = a \wedge b$. \paragraph{How this would be interpreted in failure analysis} -In failure analysis, $R2$ is the symptom of either failure~mode $A$ or $C$ -occurring. $R1$ is the symptom of $B$ or $A \wedge C$ occurring. -There is an additional symptom, that of the test case in $A \wedge B$. +In failure analysis, $R2$ is the symptom of either failure~mode $a$ or $c$ +occurring. $R1$ is the symptom of $b$ exclusive-or $a \wedge c$ occurring. +The third FMG or symptom shown is test case in $a \wedge b$. +This diagram is incomplete, there is no test case for the fault mode $a$. +The `available region' $a\\b$ has no test case, and this would be considered a `syntax error' +by the FMMD software tool. @@ -537,7 +575,7 @@ There is an additional symptom, that of the test case in $A \wedge B$. Very often a failure mode can only occurr given a searate environmental condition. -In Fault Tree Analysis (FTA) this is represented by an inhibit gate. +In Fault Tree Analysis (FTA) this is represented by an inhibit gate.\cite{NASA},\cite{NUK} \begin{figure}[h] \centering @@ -559,7 +597,7 @@ that for failure~mode $C$ to occur failure mode $A$ must have occurred. A well known example of this is the space shuttle `O' ring failure that caused the 1986 challenger disaster \cite{wdycwopt}. -For the failure mode to occurr the ambiant temperature had to +For the failure mode to occur the ambient temperature had to be below a critical value. If we take the failure mode of the `O' ring to be $C$ and the temperature below critical to be $A$, we can see that @@ -746,24 +784,28 @@ The intention for these diagrams is that they are used to collect component faults and combinations thereof, into faults that, at the module level have the same symptoms. -\subsection{Example Sub-system} +The act of collecting common symptoms by joining lines is seen as intuitive. +Syntax checking (looking for contradictions and tautologies), as well as detecting +errors of ommission are automated in the FMMD tool. -For instance were a `power supply' being analysed there could be several -individual component faults or combinations that lead to -a situation where there is no power. This can be described as a state -of the powersupply being modeelled as NO\_POWER. -These can all be collected by DISJUCNTION, i.e. that this this or this -fault occuring will cause the NO\_POWER fault. Visually this disjuction is -indicated by the joining lines. -As far as the user of the `power supply' is concerned, the power supply has failed -with the failure mode $NO\_POWER$. -The `power supply' module, after this process will have a defined set of -fault modes and may be considered as a component at a higher -level of abstraction. This module can then be combined -with others at the same abstraction level. -Note that because this is a fault collection process -the number of component faults for a module -must be less than or equal to the sum of the number of component faults. +%\subsection{Example Sub-system} +% +%For instance were a `power supply' being analysed there could be several +%individual component faults or combinations that lead to +%a situation where there is no power. This can be described as a state +%of the powersupply being modeelled as NO\_POWER. +%These can all be collected by DISJUCNTION, i.e. that this this or this +%fault occuring will cause the NO\_POWER fault. Visually this disjuction is +%indicated by the joining lines. +%As far as the user of the `power supply' is concerned, the power supply has failed +%with the failure mode $NO\_POWER$. +%The `power supply' module, after this process will have a defined set of +%fault modes and may be considered as a component at a higher +%level of abstraction. This module can then be combined +%with others at the same abstraction level. +%Note that because this is a fault collection process +%the number of component faults for a module +%must be less than or equal to the sum of the number of component faults. %Typeset in \ \ {\huge \LaTeX} \ \ on \ \ \today diff --git a/logic_diagram/repeated.dia b/logic_diagram/repeated.dia new file mode 100644 index 0000000..0f30cea Binary files /dev/null and b/logic_diagram/repeated.dia differ diff --git a/logic_diagram/repeated.fig b/logic_diagram/repeated.fig deleted file mode 100644 index 8c279c6..0000000 --- a/logic_diagram/repeated.fig +++ /dev/null @@ -1,27 +0,0 @@ -#FIG 3.2 Produced by xfig version 3.2.5 -Landscape -Center -Metric -A4 -100.00 -Single --2 -1200 2 -5 1 0 1 0 7 50 -1 -1 0.000 0 1 0 0 5173.463 2296.817 3555 2430 5310 3915 6795 2385 -5 1 0 1 0 7 50 -1 -1 0.000 0 0 0 0 6772.500 3082.500 5715 2070 6840 1620 7830 2070 -1 3 0 1 0 7 50 -1 -1 0.000 1 0.0000 1980 2205 1011 1011 1980 2205 2835 2745 -1 3 0 1 0 7 50 -1 -1 0.000 1 0.0000 3150 2205 1028 1028 3150 2205 4095 2610 -1 3 0 1 0 7 50 -1 -1 0.000 1 0.0000 6255 2070 1070 1070 6255 2070 7245 2475 -1 3 0 1 0 7 50 -1 -1 0.000 1 0.0000 7515 2115 1138 1138 7515 2115 8595 2475 -4 0 0 50 -1 0 12 0.0000 4 75 105 2430 2520 *\001 -4 0 0 50 -1 0 12 0.0000 4 75 105 6795 2340 *\001 -4 0 0 50 -1 0 12 0.0000 4 75 105 7785 2340 *\001 -4 0 0 50 -1 0 12 0.0000 4 75 105 5670 2340 *\001 -4 0 0 50 -1 0 12 0.0000 4 75 105 3510 2385 *\001 -4 0 0 50 -1 0 12 0.0000 4 135 135 1620 1035 A\001 -4 0 0 50 -1 0 12 0.0000 4 135 135 2970 945 B\001 -4 0 0 50 -1 0 12 0.0000 4 135 135 5985 810 A\001 -4 0 0 50 -1 0 12 0.0000 4 135 135 7515 810 C\001 -4 0 0 50 -1 0 12 0.0000 4 135 240 4770 3690 R1\001 -4 0 0 50 -1 0 12 0.0000 4 135 240 5985 1800 R2\001 -4 0 0 50 -1 0 12 0.0000 4 135 240 2340 2160 R3\001 diff --git a/logic_diagram/repeated.jpg b/logic_diagram/repeated.jpg index 325f0e1..b0fe9a1 100644 Binary files a/logic_diagram/repeated.jpg and b/logic_diagram/repeated.jpg differ