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1.1 Fault Diagnosis Introduction
Figure 1.1: The role of fault diagnosis in a dependable operation.
1.1 Fault Diagnosis
It is practically impossible to develop a complex system that is free from faults. These faults could
lead to failures; the undesirable situation that the system does not perform its intended function.
Fault tolerance techniques aim at the preservation of a dependable operation in the presence of
faults. Fault diagnosis is one of these techniques. Error detection and fault recovery include other
techniques to achieve fault tolerance and should not be confused with fault diagnosis techniques.
Error detection identifies the presence of a fault. Fault diagnosis is one step later; it identifies the
cause of an error. Fault diagnosis is important, because when the the cause of a failure is known,
it is possible to transform a faulty system state into a healthy system state (fault recovery). For
example, by replacing broken components with healthy components. Preferably, fault diagnosis
prevents healthy components or even the entire system from being replaced. This means error
detection, fault diagnosis, and fault recovery are interrelated. Figure 1.1 shows the the role of each
in achieving a dependable operation. The dashed circle in the figure delimits the main topic of this
thesis: fault diagnosis. Systems consists of software, hardware and mechanical components. The
focus of this thesis is on hardware. Because the hardware discussed in this thesis is part of Philips
Cardio-Vascular X-Ray System, the next subsection presents today’s approach to fault diagnosis at
PMS.
1.1.1 Fault Diagnosis at PMS
Philips Cardio-Vascular X-Ray System is a safety critical system. For this reason, it is a prime
concern to avoid catastrophic consequences for users and the environment. That is why certain
error detection mechanisms - the ones detecting errors that could result in failures harming doctors
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