114 lines
5.1 KiB
TeX
114 lines
5.1 KiB
TeX
%% INTRO
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% the problem
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% the solution
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% why you would want to read the paper
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The certification process of safety critical products for European and
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other international standards often demand environmental stress,
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endurance and Electro Magnetic Compatibility (EMC) testing. Theoretical, or `static~testing',
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is often also required. Failure Mode effects Analysis (FMEA) is a tool used
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for static testing. Its use is traditionally applied to hardware (electrical and mechanical) systems.
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With the increasing use of micro-controllers in smart~instruments and control~systems,
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software is increasingly being seen as the `missing~factor' in FMEA analysis.
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This paper takes a simple example of a hardware/software hybrid (an industry standard {\ft} input), analyses it
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using hardware and software FMEA, and then discusses the effectiveness of the
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failure modelling from the perspective of the hybrid hardware/software sub-system.
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FMEA performed on mechanical and electronic
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systems can be termed Hardware FMEA (HFMEA), and on software, SFMEA.
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This paper highlights the pitfalls and benefits of applying HFMEA and SFMEA
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to a hybrid system.
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%% MIDDLE
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% some background
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% how important software is today, how there is no FMEA to encompass both software and hardware
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FMEA is a bottom-up technique that aims to assess the effect all
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component failure modes on a system.
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It is used both as a design tool (to determine weaknesses), and is a requirement of certification of safety critical products.
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FMEA has been successfully applied to mechanical, electrical and hybrid electro-mechanical systems.
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Work on SFMEA is beginning, but
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at present no technique for SFMEA that
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integrates hardware and software models %known to the authors
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exists.
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Software in current embedded systems practise sits on top of most modern safety critical control systems [and inside many
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data collection/actuator modules (smart~instruments)], and defines their most important system wide behaviour, interfaces and communications.
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Currently standards that demand FMEA for hardware (e.g. EN298, EN61508),
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do not specify it for software, but instead specify, computer architecture, good software practise,
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review processes and language feature constraints.
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Where FMEA % scientifically
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traces component {\fms}
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to resultant system failures, software has been left in a non-analytical
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limbo of best practises and constraints.
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Where SFMEA has been applied---for some automotive and highly safety critical systems---it has always been
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performed separately from HFMEA.
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The {\ft} input circuitry used in the example and its related software, are accepted practise and in common use, and therefore the failure mode
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behaviour is well known and understood.
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For this reason it is a good example to use for comparing the results from the SFMEA and HFMEA methodologies
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with known failure mode behaviour from the field/direct experience of engineers.
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%% CONCLUSIONS.
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This paper presents an analysis of a simple software/hardware hybrid sub-system, the {\ft} input circuit consisting of
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a resistive element, multiplexer (MUX), Analogue to Digital Converter (ADC) and two software functions.
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The purpose of this sub-system is to convert an electrical current signal into a value for use in software.
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HFMEA is applied to the hardware (resistive element, MUX and ADC) and SFMEA to the software components (two `C' functions), producing two separate
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failure mode models for the {\ft} input.
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The two failure models are then discussed and compared with heuristic
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knowledge of {\ft} inputs, circuitry and software.
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Conclusions are then presented listing the benefits and draw-backs
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of analysing the hardware/software hybrid system using HFMEA and SFMEA.
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Authors:
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\begin{table}[h]
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\center
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\begin{tabular}{||p{3cm}|p{6cm}|p{5cm}||}
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\hline \hline
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{\em Author } & {\em Email} & {\em Institution} \\ \hline
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& & \\ \hline
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R.P. Clark & r.clark@energytechnologycontrol.com & Energy Technology Control Ltd. \\ \hline
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%R.P.Clark@brighton.ac.uk & Energy Technology Control Ltd \\ \hline
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A. Fish & Andrew.Fish@brighton.ac.uk & Brighton University, UK \\ \hline
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C. Garrett & C.Garrett@brighton.ac.uk & Brighton University, UK \\ \hline
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J. Howse & John.Howse@brighton.ac.uk & Brighton University, UK \\ \hline
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& & \\ \hline
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\hline
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\end{tabular}
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%\caption{Authors}
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\label{tbl:authors}
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\end{table}
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Presenting Author is R.P. Clark.
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\begin{table}[h]
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\center
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\begin{tabular}{||p{1cm}|p{10cm}|p{1cm}||}
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& Short Biography & \\ \hline
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& R.P. Clark is an embedded software Engineer, working with
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safety critical industrial burner controllers, and the design of safety critical sensors. He is currently
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working for a part-time PhD at Brighton University.
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& \\ \hline
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& & \\ \hline
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\end{tabular}
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%\caption{Authors}
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\label{tbl:bio}
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\end{table}
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