Chapter 6

Fault Detection and Isolation, Fault Tolerant Control 1

6.1. Introduction

Process automatic control has various objectives. Control performance concerns system stability (which must be guaranteed under any and all conditions), the error between reference and output in the control loops (which has implications, for instance, on product quality or motion precision), robustness against changes in the system’s parameters, or the time required to obtain a desired output. It also involves cost in an overall sense (energy or raw material consumption).

A second objective is increasingly being taken into account today by the control, which is improving the safety of the system, so as not to present any hazards to the men working close by, to the equipment or to the environment, while guaranteeing control performance. A more general term is dependability [LAP 92], used both in systems’ engineering and in computer science, and which covers the concepts of safety (the absence of catastrophic consequences), availability (readiness for correct service), reliability (continuity of correct service), integrity (the absence of improper system alteration), and maintainability (ability to undergo modifications and repairs).

Integrated automation is, therefore, not only focused on maintaining certain variables at their set-point value, but is also concerned from an overall perspective about the system and its various operating modes. These are the normal operating mode(s) and start-up or ...

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