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2.1 Preliminaries State-of-the-Practice Fault diagnosis at PMS Figure 2.1: Philips Cardio-Vascular X-Ray System 2.1.2 Introduction of the Power Supply Example This section introduces an example that is used throughout this thesis for clarifying fault diagnosis related concepts and ideas. The Cardio-Vascular X-Ray System is a complex system that has dozens of components. Consequently, the power supply of all electrical components has quite some complexity. Figure 2.2 partially shows the architecture of the system in respect to the power supply. The idea is to keep it simple, and therefore it is not complete in its depicted components. On the left, the most important power supply of the Cardio-Vascular X-Ray System, the so-called Power Distribution Unit, is shown. Its function is to switch on the various subsystems by supplying voltage (230V). The components on the right (Flat Detector, TBCB, CRCB, Collimator, Chiller) are all components that need voltage. Their behavior is beyond the scope of this thesis. The function of the component in between, the chameleon, is to provide part of the components with low voltages (24V). From now on, this example is referred to as the power supply example. The power supply example is used in Chapter 3 for introducing various automated approaches to fault diagnosis. Chapter 4 uses it to show a realistic example of model-based diagnosis applied to the Philips Cardio-Vascular X-Ray System. The following preliminary section also uses the power supply example in order to introduce some fault diagnosis related concepts. 2.1.3 Faults, Errors and Failures The previous section introduced a subsystem of the Philips Cardio-Vascular X-Ray System. Notice that the term subsystem refers to a subset of interrelated components within the X-ray system, and not to the subsystem decomposition as defined in the system design document [16] of the X-Ray System. This section uses power supply example to introduce notions related to fault diagnosis. Fault diagnosis is a mean to deal with the threats to a dependable operation; faults, errors and failures. It is important that the reader fully understands these concepts, because these are part of 10
State-of-the-Practice Fault diagnosis at PMS 2.1 Preliminaries Figure 2.2: Partial architecture of the power supply. the environment of any fault diagnosis technique. Consider the power supply example. The function of the power supply subsystem is: if the power distribution unit, all cables, all fuses and components themselves are ”healthy”, the Flat Detector, TBCB, CRCB, Collimator and Chiller are on if the system is switched on. This healthy case is referred to as the intended, or nominal behavior. If something in the system is broken the system is ”unhealthy”, and shows other behavior than the nominal behavior. This behavior is unexpected and preceded by a transition of correct functioning to malfunctioning. Such a transition is called a failure. A failure is defined as an event that occurs when the delivered service deviates from correct service [4]. Due to a failure the operator is unable to perform certain functions of the system. For example, the operator is unable to generate images of a patient’s vasculars. The reason for this is that after a failure the external system state of the system deviates from the correct system state. Here, it is assumed that the deviations are part of the state of the power supply example, as shown in Figure 2.2. Suppose the deviation from the correct system state is that TBCB, CRCB and Collimator are off, while they should be on. This is called the error. An error is defined as the deviation between external system state and correct system state [4]. In fault diagnosis, it is common to use the word symptom instead of error. The terms symptom and error are interchangeable. The cause of error is called a fault. An example of a fault that could cause an error in the power supply example is the malfunctioning of CableB. A fault is defined as the adjudged or hypothesized cause of an error [4]. In respect to the result of a fault diagnosis process, a fault is called a diagnosis. Like the terms error and symptom, the terms diagnosis and fault are interchangeable. There are many classes and types of faults (see [4]). A fault could refer to the malfunctioning of a component, but it could just as well refer to particular causes why a component malfunctions. However, in a company that uses many third party components in its systems, it is likely that these low-level details are unknown. Therefore, fault diagnosis at PMS aims to identify 11
Page 1: Automated Fault Diagnosis at Philip
Page 4 and 5: © 2006 W.M. Lindhoud. Document gen
Page 7: Preface The work presented in this
Page 10 and 11: CONTENTS 4.4 Modeling . . . . . . .
Page 13: List of Tables 3.1 Evaluation appro
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Page 48 and 49: 4.1 Fundamentals Model-Based Fault
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Diagnosing the Beam Propeller Movem
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Chapter 6 Conclusions and Recommend
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Conclusions and Recommendations 6.2
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BIBLIOGRAPHY [12] Johan de Kleer an
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Appendix A Glossary of terms In thi
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Glossary of terms • Diagnostic Pe
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Glossary of terms • Model: an abs
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Glossary of terms • System: an en
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B.2 System Data Case Study Details
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B.4 Full List of Examined Fault Sce
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B.5 Discretization of Implementatio
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C.1 The Synthetic Models that are U
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C.2 Model of the Power Supply Examp
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C.3 The Models Constructed for the
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Appendix D State-of-the-Future Faul
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