diff --git a/component_failure_modes_definition/component_failure_modes_definition.tex b/component_failure_modes_definition/component_failure_modes_definition.tex index 0bb440b..7023747 100644 --- a/component_failure_modes_definition/component_failure_modes_definition.tex +++ b/component_failure_modes_definition/component_failure_modes_definition.tex @@ -4,22 +4,26 @@ \ifthenelse {\boolean{paper}} { \abstract{ -This paper defines what is meant by the terms +This paper defines %what is meant by +the terms components, derived~components, functional~groups, component fault modes and `unitary~state' component fault modes. %The application of Bayes theorem in current methodologies, and %the suitability of the `null hypothesis' or `P' value statistical approach %are discussed. The general concept of the cardinality constrained powerset is introduced -and calculations for it corrected for the `unitary state' fault mode conditions. +and calculations for it described, and then for +calculations under `unitary state' fault mode conditions. Data types and their relationships are described using UML. Mathematical constraints and definitions are made using set theory.} } { \section{Overview} -This chapter defines what is meant by the terms +This chapter defines %what is meant by +the terms components, derived~components, functional~groups, component fault modes and `unitary~state' component fault modes. The general concept of the cardinality constrained powerset is introduced -and calculations for it corrected for the `unitary state' fault mode conditions. +and calculations for it described, and then for +calculations under `unitary state' fault mode conditions. Data types and their relationships are described using UML. Mathematical constraints and definitions are made using set theory. } @@ -30,9 +34,9 @@ This chapter describes the data types and concepts for the Failure Mode Modular When analysing a safety critical system using this technique, we need clearly defined failure modes for all the components that are used to model the system. -These failure modes have a constraint such that +In our model we have a constraint that the component failure modes must be mutually exclusive. -When this constraint is complied with we can use the FMMD process to +When this constraint is complied with we can use the FMMD method to build hierarchical bottom-up models of failure mode behaviour. %This and the definition of a component are %described in this chapter. @@ -47,7 +51,7 @@ build hierarchical bottom-up models of failure mode behaviour. %% Paragraph component and its relationship to its failure modes %% -\section{ Defining the term `Component' } +\section{ Defining the term Component } \begin{figure}[h] @@ -59,7 +63,8 @@ build hierarchical bottom-up models of failure mode behaviour. \end{figure} Let us first define a component. This is anything which we use to build a -product or system with. This could be something quite complicated +product or system with. +It could be something quite complicated like an integrated microcontroller, or quite simple like the humble resistor. We can define a component by its name, a manufacturers' part number and perhaps @@ -75,27 +80,26 @@ The UML diagram in figure structure with its associated failure modes. From this diagram we see that each component must have at least one failure mode. -Also to clearly show that the failure modes are unique events associated with one component, +To clearly show that the failure modes are unique events associated with one component, each failure mode is referenced back to only one component. -This modelling constraint is due to the fact that even generic components with the same -failure mode types, may have different statistical MTTF properties within the same -circuitry\footnote{For example, consider resistors one of high resistance and one low. -The generic failure modes for a resistor will be the same for both. -The lower resistance part will draw more current and therefore have a statistically higher chance of failure.}. -%% sharing failure modes arrrgghh so irrelevant -%% wrong as well perhaps, as each component will have environmental constraints -%% that determine its statistical behaviour. A 1 Meg ohm resistor -%% is less stressed than a 100 ohm in the same circuit etc -% Perhaps talk here about the failure modes being shared, but by being referenced -% by the component ? +%%-%% MTTF STATS CHAPTER MAYBE ?? +%%-%% +%%-%% This modelling constraint is due to the fact that even generic components with the same +%%-%% failure mode types, may have different statistical MTTF properties within the same +%%-%% circuitry\footnote{For example, consider resistors one of high resistance and one low. +%%-%% The generic failure modes for a resistor will be the same for both. +%%-%% The lower resistance part will draw more current and therefore have a statistically higher chance of failure.}. A product naturally consists of many components and these are traditionally kept in a `parts list'. For a safety critical product this is usually a formal document and is used by quality inspectors to ensure the correct parts are being fitted. For our UML diagram the parts list is simply a collection of components -as shown in figure \ref{fig:componentpl}. +as shown in figure \ref{fig:componentpl}. The parts list is shown for +completeness here, as people involved with PCB and electronics production, verification +and testing would want to know where it lies in the model. +The parts list is not actively used in the FMMD method. \begin{figure}[h] \centering \includegraphics[width=400pt,bb=0 0 712 68,keepaspectratio=true]{component_failure_modes_definition/componentpl.jpg}