From 75cb65c596191f68c58ee22175a88cdfdc075e51 Mon Sep 17 00:00:00 2001 From: Robin Clark Date: Sat, 4 Feb 2012 13:19:56 +0000 Subject: [PATCH] Notes and skeleton chapters. --- .../component_failure_modes_definition.tex | 25 ++++++++++++++++--- .../symptom_abstraction.tex | 8 +++--- 2 files changed, 26 insertions(+), 7 deletions(-) diff --git a/old_thesis/component_failure_modes_definition/component_failure_modes_definition.tex b/old_thesis/component_failure_modes_definition/component_failure_modes_definition.tex index 341a64d..201eefe 100644 --- a/old_thesis/component_failure_modes_definition/component_failure_modes_definition.tex +++ b/old_thesis/component_failure_modes_definition/component_failure_modes_definition.tex @@ -86,7 +86,7 @@ defines a `part' thus The term component, in American English, can mean a building block or a part. In British-English a component generally is given to mean the definition for part above. For this study, we will use {\bc} to mean a `part', and component -to mean a part or sub-assembly. +to mean a part or a sub-assembly. What components all have in common is that they can fail, and fail in a number of well defined ways. For common base-components @@ -146,9 +146,9 @@ When building from the bottom up, it is more meaningful to call them `derived~co \section{Failure Modes in depth: A detailed look at the op-amp and the resistor} -We look in detail at two common electrication components in this section and examine how +We look in detail at two common electrical components in this section and examine how two sources of information on failure modes view their failure mode behaviour. -We look at the reasons why some known failure modes are ommitted, or presented in +We look at the reasons why some known failure modes are omitted, or presented in specific but unintuitive ways. - Failure modes. Prescribed failure modes EN298 - FMD91 @@ -156,14 +156,28 @@ specific but unintuitive ways. \subsection{resistor} EN298 says...... -Parameter change not considereed for EN298 because the resistors are downrated from +Parameter change not considered for EN298 because the resistors are down-rated from maximum possible voltage exposure -- find refs. + +FMD-91 gives the following percentatges for failure rates in +\label{downrate} +The parameter change, is usually a failure mode associated with over stressing the component. +In a system designed to typical safety critical constraints (as in EN298) +these environmentally induced failure modes need not be considered. + \subsection{op-amp} Literature suggests, latch up, latch down and oscillation. FMD-91 states, V+ disconnected, V- V+ shorted, NOOP and Low slew. +EN298 does not specifgically include OP_AMPS and these would fall under +table \cite{en298}[A.1 note e]. +This demands that all open connections, and shorts between adjacent pins be considered. +We can examine these failure modes by taking our 358 op-amp and examining + + + looking at Discuss why. Determine more user friendly terms from FMD91 definition. @@ -887,6 +901,9 @@ levels of electrical interference, high voltage contamination on supply lines, radiation levels etc. Environmental influences will affect specific components in specific ways. Environmental analysis is thus applicable to components. +Environmental influences, such as over stress due to voltage +can be eliminated by down-rating of components as discussed in section~\ref{downrate}. +With given environmental constraints, we can therefore eliminate some failure modes from the model. \paragraph{Operational states.} Within the field of safety critical engineering we often encounter sub-system that include test facilities. We also encounter degraded performance diff --git a/old_thesis/symptom_abstraction/symptom_abstraction.tex b/old_thesis/symptom_abstraction/symptom_abstraction.tex index f2cf60d..2764172 100644 --- a/old_thesis/symptom_abstraction/symptom_abstraction.tex +++ b/old_thesis/symptom_abstraction/symptom_abstraction.tex @@ -97,12 +97,12 @@ When all test cases have been analysed, we switch our attention to a higher abst % Each `test case' is labelled from the perspective of the failure as seen at sub-system level. % -We can now try to simplfy by determining common symptoms. +We can now try to simplify by determining common symptoms. A common symptom, in this context, is defined as faults caused by different component failure modes that have the same effect from the perspective of a `user' of the sub-system. -Test case results can now viewed as failure modes of the sub-sytem or `black box', and grouped together +Test case results can now viewed as failure modes of the sub-system or `black box', and grouped together where there are common symptoms. These are grouped together by joining them with lines. These lines form collected groups (or `spiders'). See figure \ref{fig:gensubsys3}. @@ -320,7 +320,7 @@ In other words we have derived failure modes for this sub-system. % is represented as a contour. These contours represent the failure modes of the sub-system. % \end{itemize} -This sub-system may now therfore, be represented as three separate failure modes. +This sub-system may now therefore, be represented as three separate failure modes. We may now treat this sub-system as we would a component with a known set of failure modes. The failure modes of the Sub-system $SS$ are now the set $SS_{fm} = \{ SP1, SP2, SP_3 \}$. @@ -365,7 +365,9 @@ with known failure modes. +\section{Boolean definition of a symptom} +Need to explain why its XOR not OR here. \section{To conclude}