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JMC proof read

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Robin Clark 2012-06-19 17:59:20 +01:00
parent 82f6f50d9b
commit 9a2b15345d
1 changed files with 13 additions and 10 deletions
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23
papers/fmmd_software_hardware/software_fmmd.tex
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@ -101,7 +101,7 @@ failure mode of the component or sub-system}}}
\setlength{\headsep}{0in} \setlength{\headsep}{0in}
%\setlength{\textheight}{22cm} %\setlength{\textheight}{22cm}
\setlength{\textwidth}{18cm} \setlength{\textwidth}{18cm}
\setlength{\textheight}{24.5cm} \setlength{\textheight}{24.35cm}
%\setlength{\textwidth}{20cm} %\setlength{\textwidth}{20cm}
\setlength{\oddsidemargin}{0in} \setlength{\oddsidemargin}{0in}
\setlength{\evensidemargin}{0in} \setlength{\evensidemargin}{0in}
@ -171,20 +171,23 @@ Currently standards that demand FMEA for hardware (e.g. EN298, EN61508),
do not specify it for software, but instead specify, good practise, do not specify it for software, but instead specify, good practise,
review processes and language feature constraints. review processes and language feature constraints.
% %
This is a weakness This is a weakness.
Where FMEA % scientifically Where FMEA % scientifically
traces component {\fms} traces component {\fms}
to resultant system failures, software has been left in a non-analytical to resultant system failures, software has been left in a non-analytical
limbo of best practises and constraints. limbo of best practises and constraints.
% % % %
If software and hardware integrated FMEA were possible, electro-mechanical-software hybrids could If software and hardware integrated FMEA were possible, electro-mechanical-software hybrids could
be modelled; and could thus be `complete' failure mode models. be modelled, and could thus be `complete' failure mode models.
%
Failure modes in components in say a sensor, could be traced Failure modes in components in say a sensor, could be traced
up through the electronics and then through the controlling software. up through the electronics and then through the controlling software.
%
Presently FMEA, stops at the glass ceiling of the computer program. Presently FMEA, stops at the glass ceiling of the computer program.
%
This paper presents a modular variant of FMEA, Failure Mode Modular De-Composition (FMMD), a methodology which This paper presents a modular variant of FMEA, Failure Mode Modular De-Composition (FMMD), a methodology which
can be applied to software, and is compatible can be applied to software, and is compatible
and integrate-able with FMMD performed on mechanical and electronic systems. and integrable with FMMD performed on mechanical and electronic systems.
} }
%\today %\today
@ -213,7 +216,7 @@ and unstructured non-functional languages}.
%What FMEA is, briefly variants... %What FMEA is, briefly variants...
Failure Mode effects Analysis is the process of taking Failure Mode Effects Analysis is the process of taking
component failure modes, and by reasoning, tracing their effects through a system component failure modes, and by reasoning, tracing their effects through a system
and determining what system level failure modes could be caused. and determining what system level failure modes could be caused.
% %
@ -268,7 +271,7 @@ In a complicated system, mapping a component failure mode to a system level fail
will mean a long reasoning distance; that is to say the actions of the failed component will have to be traced through will mean a long reasoning distance; that is to say the actions of the failed component will have to be traced through
several sub-systems and the effects of other components on the way. several sub-systems and the effects of other components on the way.
% %
With software at the higher levels of these sub-systems With software at the higher levels of these sub-systems,
we have yet another layer of complication. we have yet another layer of complication.
% %
In order to integrate software, %in a meaningful way In order to integrate software, %in a meaningful way
@ -504,8 +507,8 @@ to supply a current signal to represent the value to be sent~\cite{aoe}[p.934].
Usually, $4mA$ represents a zero or starting value and $20mA$ represents the full scale, Usually, $4mA$ represents a zero or starting value and $20mA$ represents the full scale,
and this is referred to as {\ft} signalling. and this is referred to as {\ft} signalling.
% %
{\ft} has a an electrical advantage as well, because the current in a loop is constant~\cite{aoe}[p.20] {\ft} has an electrical advantage as well, because the current in a loop is constant~\cite{aoe}[p.20].
resistance in the wires between the source and the receiving end is not an issue Thus resistance in the wires between the source and the receiving end is not an issue
that can alter the accuracy of the signal. that can alter the accuracy of the signal.
% %
This circuit has many advantages for safety. If the signal becomes disconnected This circuit has many advantages for safety. If the signal becomes disconnected
@ -646,7 +649,7 @@ double read_ADC( int channel ) {
/* return out of range result */ /* return out of range result */
/* if invalid channel selected */ /* if invalid channel selected */
if ( channnel > ADC_CHAN_RANGE ) if ( channel > ADC_CHAN_RANGE )
return -2.0; return -2.0;
/* set the multiplexer to the desired channel */ /* set the multiplexer to the desired channel */
ADCMUX = channel; ADCMUX = channel;
@ -964,7 +967,7 @@ of reasoning for each component failure mode.
% %
% Part of the design philosophy of a {\ft} loop, is that % Part of the design philosophy of a {\ft} loop, is that
% if anything goes wrong, we should be able to detect it. % if anything goes wrong, we should be able to detect it.
% In fact unless all electrical elements in the loop % In fact, unless all electrical elements in the loop
% are in working order we will detect a failure in % are in working order we will detect a failure in
% the majority of cases. % the majority of cases.
% \paragraph{Sending side of a {\ft} loop} % \paragraph{Sending side of a {\ft} loop}