Modelling for fault detection and isolation versus modelling for control

The main purpose of this paper is to emphasize the particularities of model s needed for model-based fault detection and isolation (FDI) in contrast to the models used for control. Of special interest is the question of comple xity of the model, which is of great importance for the practical implement ation. This, of course, depends basically on the given situation such as th e kind of plant, the measurements, the kind and number of faults to be dete cted and the demands for fault isolation and robustness. However, the paper shows that diagnostic models, in contrast to the wide-spread opinion that those have always to be more complex than the functional models for control , may be even less complex, because they are restricted to only those parts of the system in which the faults occur. The issue of model complexity is discussed in terms of different model-based FDI approaches - analytical, kn owledge-based and data-based. The ideas are illustrated in a case study, wh ere several types of model-based FDI techniques are compared with the same plant, the amira three tank system.