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ARRARARARRAGGHHHHH going mad

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removing we from sentences. TORTURE
MENTAL TORTURE
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Robin Clark 2013-09-08 18:38:48 +01:00
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9
mybib.bib
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@ -941,7 +941,6 @@ ISSN={1530-2059},}
YEAR = "1988"
}
@book{DBLP:books/ph/KernighanR88,
author = {Brian W. Kernighan and
Dennis Ritchie},
@ -1136,6 +1135,14 @@ ISSN={0098-5589},}
}
@MISC{microchipreliability,
author = "Microchip",
title = "Microchip: Reliability Data Search Engine: Annual Product Reliability Reports",
howpublished = "Microchip Inc. http://www.microchip.com/reliabilityreport/Default.aspx",
year = "2013"
}
@MISC{javaarea,
author = "Sun~Micro~Systems",
title = "Java Area Operations",

170
submission_thesis/CH2_FMEA/copy.tex
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@ -24,11 +24,11 @@ are examined in the context of two sources of information that define failure mo
To introduce the concept of FMEA, a simple example is given, using a hypothetical four to twenty milli-amp ({\ft}) %milli-amp
reader.
%
The four main current FMEA variants are described and we develop %conclude by describing concepts
The four main current FMEA variants are described %and we develop %conclude by describing concepts
the concepts
that underlie the usage and philosophy of FMEA.
that underlie the usage and philosophy of FMEA discussed.
%
We return to the overall process of FMEA and model it using UML.
The overall process of FMEA is then reviewed and modelled using UML.
%
By using UML
the entities needed to implement FMEA
@ -95,11 +95,12 @@ function that they perform.
We begin FMEA with the basic, or starting components.
%
These components are the sort we buy in or consider as pre-assembled modules.
We term these the {\bcs}; they are considered ``atomic'' i.e. they are not broken down further.
These components are the sort bought in or considered as pre-assembled modules.
These are termed {\bcs}; they are considered ``atomic'' i.e. they are not broken down further.
%
Firstly we need to know how these can fail, so our first relationship
is between a {\bc} and its failure modes, see figure~\ref{fig:component_fm_rel}.
The first requirement for a {\bc} is to define the ways in which it can fail,
this relationship %between a {\bc} and its failure modes,
is shown in figure~\ref{fig:component_fm_rel}.
\fmmdglossBC
%DIAGRAM of Base components and failure modes
@ -114,8 +115,8 @@ is between a {\bc} and its failure modes, see figure~\ref{fig:component_fm_rel}.
The next stage is analysis, that is reasoning applied to the system in the event of
a given failure mode.
%
To perform this we need to know how a failure
mode, considering its effect on other components in the system,
To perform how a failure
mode, after considering its effect on other components in the system,
will translate to a system level symptom/failure.
%
The result of FMEA is to determine system level failures,
@ -147,17 +148,23 @@ of this chapter.
\fmmdglossBC
\label{sec:determine_fms}
\fmodegloss
In order to apply any form of FMEA we need to know the ways in which
the {\bcs} we are using can fail. In practise, this part of the process is guided by
the standards to which we are seeking to conform.% to.
In order to apply any form of FMEA the ways in which
the {\bcs}\footnote{A good introduction to hardware and software failure modes may be found in~\cite{sccs}[pp.114-124].} %used
can fail must be clearly defined.
%
\footnote{A good introduction to hardware and software failure modes may be found in~\cite{sccs}[pp.114-124].}
In practise, this part of the process is guided by
the particular standard
which is being conformed to. %we are seeking to conform.% to.
%
Typically, when choosing components for a design, we look at manufacturers' data sheets
Standards may differ in their definitions for the {\fms} of {\bcs}.
The reasons for these differences are examined below using two example components.
%
%
Typically, when choosing components for a design, engineers will look at manufacturers' data sheets
which describe functionality, physical dimensions,
environmental ranges, tolerances and by `reading~between~the~lines'
in some cases can indicate how a component may fail/misbehave
under given conditions.
in some cases can indicate how a component may fail/misbehave.
%under given conditions.
%
How %base
components could fail internally, is not of interest to an FMEA investigation.
@ -168,8 +175,10 @@ A large body of literature exists giving guidance for the determination of comp
For this study FMD-91~\cite{fmd91} and the gas burner standard EN298~\cite{en298} are examined.
%Some standards prescribe specific failure modes for generic component types.
In EN298 failure modes for most generic component types are listed, or if not listed,
are determined using a procedure where we consider
all pins open and then all adjacent pins shorted.
are determined using a procedure:
typically of the form of examining scenarios such as
`all~pins~open' and then `all~adjacent~pins~shorted'~\cite{en298}[A.1 note e].
%a procedure where failure scenarios of all pins OPEN and all adjacent pins shorted
%are examined.
%
@ -185,9 +194,18 @@ component {\fms} suitable for use in FMEA.
A third document, MIL-1991~\cite{mil1991} provides overall reliability statistics for
component types, but does not detail specific failure modes.
%
Using MIL1991 in conjunction with FMD-91 we can determine statistics for the failure modes
Using MIL1991 in conjunction with FMD-91 statistics can be determined for the failure modes
of component types.
%
As these documents are now a little old, the results
from them can be on the conservative side.
\frategloss
\fmmdglossFIT
%
A FIT value for a micro-processor
may be determined at around 100 using these documents for instance, but
FIT claims for modern integrated micro-controllers are typically less than five~\cite{microchipreliability}.
%
The FMEA variant\footnote{EN61508 (and related standards) are based on the FMEA variant Failure Mode Effects and Diagnostic Analysis (FMEDA)}
used for European standard EN61508~\cite{en61508}
requires statistics for Meantime to Failure (MTTF) for all {\bc} failure modes.
@ -211,22 +229,25 @@ requires statistics for Meantime to Failure (MTTF) for all {\bc} failure modes.
\section{Determining the failure modes of Components.}
\fmodegloss
The starting point in the FMEA process are the failure modes of the components
we would typically find in a production parts list, which we can term the {\bcs}.
The starting points in the FMEA process are the failure modes of the {\bcs}.
%s
%Typically found in a production parts list, which are termed the {\bcs}.
%
In order to define FMEA we must start with a discussion on how these failure modes are chosen.
In order to define FMEA, a discussion on how these failure modes are defined and
their relationship to particular standards is presented below.
%
In this section we pick %look in detail at
two common electrical components as examples, and examine how
the two chosen sources of {\fm} information define their failure mode behaviour.
We look at the reasons why some known failure modes % are omitted, or presented in
%specific but unintuitive ways.
%We compare the US. military published failure mode specifications wi
can be found in one source but not in the others and vice versa.
%In this section we pick %look in detail at
Two common electrical components are used as examples,
and examined against two sources of {\fm} information. % define their failure mode behaviour.
%
Finally we compare and contrast the failure modes determined for these components
These definitions for a given generic component may not always agree.
%
The reasons why some {\fms}
can be found in one source but not in the others and vice versa, are discussed.
%
Finally the failure modes determined %for these components
from the FMD-91~\cite{fmd91} reference source and from the guidelines of the
European burner standard EN298~\cite{en298}.
European burner standard EN298~\cite{en298} are compared and contrasted.
\subsection{Failure mode determination for generic resistor.}
\label{sec:resistorfm}
@ -238,14 +259,14 @@ The resistor is a ubiquitous component in electronics, and is therefore a good c
%
FMD-91\cite{fmd91}[3-178] lists many types of resistor
and lists many possible failure causes.
For instance for {\textbf{Resistor,~Fixed,~Film}} we are given the following failure causes:
For instance for {\textbf{Resistor,~Fixed,~Film}} the following failure causes are given:
\begin{itemize}
\item Opened 52\%
\item Drift 31.8\%
\item Film Imperfections 5.1\%
\item Substrate defects 5.1\%
\item Shorted 3.9\%
\item Lead damage 1.9\%
\item Opened 52\% ,
\item Drift 31.8\% ,
\item Film Imperfections 5.1\% ,
\item Substrate defects 5.1\% ,
\item Shorted 3.9\% ,
\item Lead damage 1.9\% .
\end{itemize}
% This information may be of interest to the manufacturer of resistors, but it does not directly
% help a circuit designer.
@ -253,27 +274,27 @@ For instance for {\textbf{Resistor,~Fixed,~Film}} we are given the following fai
% against {\fms} that the resistor could exhibit.
% We can determine these {\fms} by converting the internal failure descriptions
% to {\fms} thus:
To make this useful for FMEA/FMMD we must assign each failure cause to symptomatic failure mode descriptor
as shown below.
To make this useful for FMEA/FMMD each failure cause must be mapped to a symptomatic failure mode descriptor
as listed below:
%
%and map these failure causes to three symptoms,
%drift (resistance value changing), open and short.
\begin{itemize}
\item Opened 52\% $\mapsto$ OPENED
\item Drift 31.8\% $\mapsto$ DRIFT
\item Film Imperfections 5.1\% $\mapsto$ OPEN
\item Substrate defects 5.1\% $\mapsto$ OPEN
\item Shorted 3.9\% $\mapsto$ SHORT
\item Opened 52\% $\mapsto$ OPENED,
\item Drift 31.8\% $\mapsto$ DRIFT,
\item Film Imperfections 5.1\% $\mapsto$ OPEN,
\item Substrate defects 5.1\% $\mapsto$ OPEN,
\item Shorted 3.9\% $\mapsto$ SHORT,
\item Lead damage 1.9\% $\mapsto$ OPEN.
\end{itemize}
%
We note that the main causes of resistor value drift are overloading. % of components.
Note that the main causes of resistor value drift are overloading. % of components.
This is borne out in the FMD-91~\cite{fmd91}[232] entry for a resistor network where the failure
modes do not include drift.
%
If we can ensure that our resistors will not be exposed to overload conditions, the
probability of drift (sometimes called parameter change) occurring
If it is ensured that our resistors will not be exposed to overload conditions, the
probability of drift (sometimes called parameter change) %occurring
is significantly reduced, enough for some standards to exclude it~\cite{en298,en230}.
@ -328,8 +349,8 @@ The differences in resistor failure modes between FMD-91 and EN298 are that FMD-
include the failure mode DRIFT. EN298 does not include this, mainly because it imposes circuit design constraints
that effectively side step that problem.
%
For this study we will take the conservative view from EN298, and consider the failure
modes for a generic resistor to be both OPEN and SHORT. We use the function $fm$
For this study the conservative view from EN298 is taken, and the failure
modes for a generic resistor taken to be both OPEN and SHORT. The function $fm$ is used
to return a set of failure modes,
i.e.
\label{ros}
@ -348,7 +369,7 @@ $$ fm(R) = \{ OPEN, SHORT \} . $$
The operational amplifier (op-amp) %is a differential amplifier and
is very widely used in nearly all fields of modern analogue electronics.
%
Only one of two sources of information on {\bc} {\fms} we are comparing
Only one of two sources of information on {\bc} {\fms} being compared
has an entry specific to operational amplifiers (FMD-91).
%
EN298 does not specifically define the
@ -358,16 +379,17 @@ components types not specifically listed in it.
%
Operational amplifiers are typically packaged in dual or quad configurations---meaning
that a chip will typically contain two or four amplifiers.
For the purpose of example for EN298, we look at
%
For the purpose of example for EN298, %we look at
a typical op-amp designed for instrumentation and measurement, the dual packaged version of the LM358~\cite{lm358}
(see figure~\ref{fig:lm258}).
(see figure~\ref{fig:lm258}) is examined.
%
With the results from both sources of {\fm} definition %
%we compare
the failure mode definitions for FMD-91 and EN298
relating to operational amplifiers are compared.
\paragraph{ Failure Modes of an Op-Amp according to FMD-91 }
\paragraph{Failure Modes of an Op-Amp according to FMD-91.}
\fmodegloss
%Literature suggests, latch up, latch down and oscillation.
For Op-Amp failures modes, FMD-91\cite{fmd91}{3-116] states,
@ -382,38 +404,40 @@ Again these are mostly internal causes of failure, more of interest to the compo
than a test engineer % designer
looking for the symptoms of failure.
%
We need to translate these failure causes within the Op-Amp into {\fms}.
These failure causes within the Op-Amp need to be translated to symptomatic {\fms}.
%
We can look at each failure cause in turn, and map it to potential {\fms} suitable for use in FMEA
Each failure cause is examined in turn, and mapped to potential {\fms} suitable for use in FMEA
investigations.
\paragraph{Op-Amp failure cause: Poor Die attach.}
The symptom for this is given as a low slew rate. This means that the op-amp
will not react quickly to changes on its input terminals.
The symptom for this is given as a low slew rate.
%
This means that the op-amp will not react quickly to changes on its input terminals.
%
This is a failure symptom that may not be of concern in a slow responding system like an
instrumentation amplifier. However, where higher frequencies are being processed,
a signal may be lost entirely.
We can map this failure cause to a {\fm}, and we can call it $LOW_{slew}$.
This failure cause can be mapped to a symptomatic {\fm} called $LOW_{slew}$.
\paragraph{No Operation - over stress.}
Here the OP-Amp has been damaged, and the output may be held HIGH or LOW, or may be
effectively tri-stated, i.e. not able to drive circuitry in along the next stages of
the signal path: we can call this state NOOP (no Operation).
the signal path: this {\fm} is termed NOOP (no Operation).
%
We can map this failure cause to three {\fms}, $LOW$, $HIGH$, $NOOP$.
This failure cause thus maps to three {\fms}, $LOW$, $HIGH$, $NOOP$.
\paragraph{Shorted inputs: $V_+$ to $V_-$.}
Due to the high intrinsic gain of an op-amp, and the effect of offset currents,
this will force the output HIGH or LOW.
We map this failure cause to $HIGH$ or $LOW$.
This failure cause maps to $HIGH$ or $LOW$.
\paragraph{Open input: $V_+$.}
This failure cause will mean that the minus input will have the very high gain
of the Op-Amp applied to it, and the output will be forced HIGH or LOW.
We map this failure cause to $HIGH$ or $LOW$.
This failure cause maps to $HIGH$ or $LOW$.
\paragraph{Collecting Op-Amp failure modes from FMD-91.}
We can define an Op-Amp, under FMD-91 definitions to have the following {\fms}.
An Op-Amps' failure mode behaviour, under FMD-91 definitions will have the following {\fms}.
\begin{equation}
\label{eqn:opampfms}
fm(OpAmp) = \{ HIGH, LOW, NOOP, LOW_{slew} \}
@ -425,15 +449,20 @@ We can define an Op-Amp, under FMD-91 definitions to have the following {\fms}.
EN298 does not specifically define OP\_AMPS failure modes; these can be determined
by following a procedure for `integrated~circuits' outlined in
annex~A~\cite{en298}[A.1 note e].
%
This demands that all open connections, and shorts between adjacent pins be considered as failure scenarios.
We examine these failure scenarios on the dual packaged $LM358$~\cite{lm358} %\mu741$
and determine its {\fms} in table ~\ref{tbl:lm358}.
Collecting the op-amp failure modes from table ~\ref{tbl:lm358} we obtain the same {\fms}
that we got from FMD-91, listed in equation~\ref{eqn:opampfms}, except for
%
% Collecting the op-amp failure modes from table ~\ref{tbl:lm358} we obtain the same {\fms}
% that we got from FMD-91, listed in equation~\ref{eqn:opampfms}, except for
% $LOW_{slew}$.
%
Collecting the op-amp failure modes from table ~\ref{tbl:lm358} the same {\fms}
that we got from FMD-91 are obtained---listed in equation~\ref{eqn:opampfms}---except for
$LOW_{slew}$.
%\paragraph{EN298: Open and shorted pin failure symptom determination technique}
@ -636,11 +665,14 @@ Let us choose resistor R1 in the OP-AMP gain circuitry.
\item \textbf{F - Failures of given component} The resistor (R1) could fail by going OPEN or SHORT (EN298 definition).
\item \textbf{M - Failure Mode} Consider the component failure mode SHORT
\item \textbf{E - Effects} This will drive the minus input LOW causing a HIGH OUTPUT/READING
\item \textbf{A - Analysis} The reading will be out of the normal range, and we will have an erroneous milli-volt reading
\item \textbf{A - Analysis} The reading will be out of the normal range, i.e. will have an erroneous milli-volt reading
\end{itemize}
\fmeagloss
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%% WE removal project ends here today 08SEP2013 %%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
The analysis above has given us a result for % one failure %scenario i.e.
one single component failure mode.
@ -649,8 +681,10 @@ for each failure mode of all the components in the system under investigation.
%
In theory we have had to look at the failure~mode
in relation to the entire circuit.
%
We have used intuition to determine the probable
effect of this failure mode.
%
For instance we have assumed that the resistor R1 going SHORT
will not affect the ADC, the Microprocessor or the UART.
%