lunchtime work edit

component_failure_modes_definition/component_failure_modes_definition.tex

@@ -50,7 +50,7 @@ component by its name, a manufacturers part number and perhaps
 a vendors reference number.
 What these components all have in common is that they can fail, and fail in
 a number of well defined ways. For common components
-there is established literature for the failure modes for the system designer consider (with accompanying statistical
+there is established literature for the failure modes for the system designer consider (often with accompanying statistical
 failure rates)\cite{mil1991}. For instance, a simple resistor is generally considered 
 to fail in two ways, it can go open circuit or it can short.  
 Thus we can associate a set of faults to this component $ResistorFaultModes=\{OPEN, SHORT\}$.
@@ -98,24 +98,27 @@ The aim of FMMD analysis is to produce complete  failure
 models of safety critical systems  from the bottom-up,
 starting, where possible with known component failure modes.
 
+An advantage of working from the bottom up is that we can ensure that
+all component failure modes must be considered. A top down approach
+could miss individual failure modes of components.
+
 In order to analyse from the bottom-up, we need to take
 small groups of components from the parts~list that naturally
 work together to perform a simple function.
 The components to include in a  functional group are chosen by a human, the analyst.
 We can term this a `Functional~Group' and represent it as a class. When we have a 
 `Functional~Group' we can look at the failure modes of all the components
-in it and determine a failure mode behaviour for that group.
+in it and determine a failure mode model for that group.
 Or in other words we can determine the failure modes of the functional
-group. An advantage of working from the bottom up is that we can ensure that
-all component failure modes must be considered. A top down approach
-could miss individual failure modes of components.
+group. We can now consider the functional group as a sort of super component
+with a know set of failure modes.
 
 
 \subsection{From functional group to newly derived component}
 
 The process for taking a functional~group, considering
-all the failure modes of all the components in it,
-and analysing these is called `symptom abstraction' and 
+all the failure modes of all the components in the group,
+and analysing it is called `symptom abstraction' and 
 is dealt with in detail in chapter \ref{symptom_abstraction}.
 
 In terms of our UML model the symptom abstraction process takes a functional~group,
@@ -126,7 +129,7 @@ and creates a new derived component from it.
 %must consider all the failure modes of the components in the functional
 %group.
 The newly created derived~component requires a set of failure modes of its own.
-These failure modes are the failure mode behaviour of the fungtional group that it was derived from.
+These failure modes are the failure mode behaviour of the functional group that it was derived from.
 Because these new failure modes were determined from a derived component we can call 
 these `derived~failure~modes'.
 %It then creates a new derived~component object, and associates it to this new set of derived~failure~modes.
@@ -252,10 +255,9 @@ we state this formally
 % \end{equation}
 
 That is to say that it is impossible that any pair of failure modes can be active at the same time
-for the failure mode set $F$ to exists in the family of sets $U$
-
+for the failure mode set $F$ to exist in the family of sets $U$.
 Note where that are more than two failure~modes, 
-by banning pairs from being active at the same time
+by banning any pairs from being active at the same time
 we have banned larger combinations as well.
 
 
@@ -263,7 +265,7 @@ we have banned larger combinations as well.
 \section{Component Failure Modes and Statistical Sample Space}
 %\paragraph{NOT WRITTEN YET PLEASE IGNORE}
 A sample space is defined as the set of all possible outcomes.
-For a component this set of all possible outcomes are its normal correct
+For a component in FMMD analysis, this set of all possible outcomes is its normal correct
 operating state and all its failure modes.
 When dealing with failure modes, we are not interested in 
 the state where the component is working perfectly or `OK' (i.e. operating with no error).