From abb122a1a85769d15ca0a2668be4a82b6428fdec Mon Sep 17 00:00:00 2001 From: Robin Clark Date: Thu, 26 Jan 2012 19:36:08 +0000 Subject: [PATCH] added to introduction. Ill (bronchitis ~ off work ~ temperature) but still need to finish the last example circuit for C Garret --- .../opamp_circuits_C_GARRETT/opamps.tex | 43 ++++++++++++++++--- 1 file changed, 36 insertions(+), 7 deletions(-) diff --git a/old_thesis/opamp_circuits_C_GARRETT/opamps.tex b/old_thesis/opamp_circuits_C_GARRETT/opamps.tex index 9a5c5eb..41a2ad0 100644 --- a/old_thesis/opamp_circuits_C_GARRETT/opamps.tex +++ b/old_thesis/opamp_circuits_C_GARRETT/opamps.tex @@ -28,6 +28,7 @@ \begin{document} \begin{abstract} +\pagenumbering{roman} Circuits from email conversation. Not a document to be proof read. @@ -37,25 +38,54 @@ Proof of analysis concept. Function $fm$ applied to a component returns its failure modes. -The circuits specified are not typical saftey critical circuitry which usually +The circuits specified are not typical safety critical circuitry which usually has both redundancy and self~checking and/or diagnostic features build in. These are examples of the FMMD methodology being applied to some standard electronic circuits. \end{abstract} \maketitle \tableofcontents \listoffigures - - -\clearpage +\listoftables + +\clearpage \pagenumbering{arabic} \section{Basic Concepts Of FMMD} +The idea behind FMMD is to modularise, from the bottom-up, traditional FMEA techniques. +Traditional FMEA takes part failure modes and then determines what effect each of these +failure modes could have on the system under investigation. +It is worth defining clearly the term part here. +Geoffry Hall writing in space Craft Systems Engineering~\cite{scse}[p.619], defines it thus: +``{Part(definition)}---The Lowest level of assembly, beyond which further disassembly irrevocably destroys the item''. +In the field of electronics a resistor, capacitor and op-amp would fit this definition of a `part'. +Failure modes for part types can be found in the literature~\cite{fmd91}\cite{mil1991}. +Traditional FMEA, by looking at `part' level failure modes +involves what we could term a large `reasoning~distance'; that is to say +in a complex system, taking a particular failure mode, of a particular part +and then trying to predict the outcome in the context of an entire system, is +a leap~of~faith. There will be numerous possibilities of effects and side effects on +other components in the system; more than is practically possible to rigorously examine. +To simply trace a simple route from a particular part failure mode to a top level system error/symptom +oversimplifies the task of failure mode analysis, and makes the process arbitrary and error prone. + +Fortunately most real-world designs take a modular approach. In Electronics +for instance, commonly used configurations of parts are used to create +amplifiers, filters, potential dividers etc. +It is therefore natural to collect parts to form functional groups. +These commonly used configurations of parts, or {\fgs}, will +also have failure mode behaviour. We can take a {\fg} and determine its symptoms of failure. +When we have done this we can treat this as a component in its own right. +If we terms `parts' as base~components and components we have determined +from functional groups as derived components, we can modularise the FMEA task. +If we start building {\fgs} from derived components we can start to build a modular +hierarchical failure mode model. + \paragraph {Definitions} \begin{itemize} -\item {\bc} - a component with a known set of unitary state failure modes. Base here mean a starting or `bought~in' component. -\item {\fg} - a collection of components chosen to perform a particular task +\item {\bc} - is taken to mean a `part' as defined above~\cite{scse}[p.619]. We should be able to define a set of failure modes for every {\bc}. +\item {\fg} - a collection of components chosen to perform a particular task \item {\em symptom} - a failure mode of a functional group caused by one or more of its component failure modes. \item {\dc} - a new component derived from an analysed {\fg} \end{itemize} @@ -66,7 +96,6 @@ level up to the top, or system level, with analysis stages between each transition to a higher level in the hierarchy. - The first stage is to choose {\bcs} that interact and naturally form {\fgs}. The initial {\fgs} are collections of base components. %These parts all have associated fault modes. A module is a set fault~modes.