Tri-valued Evaluation of Residuals as a Method of Addressing the Problem of Fault Compensation Effect

Authors:

• Jan Maciej Kościelny,
• Michał Bartyś,
• Zofia Łabęda-Grudziak

Abstract

The fault compensation effect sets an important and up-to-date unsolved theoretical and practical problem for diagnostics of processes. Compensation of influences of faults on residual values has a significant impact on the diagnosis. On the one hand, there is a view that model-based diagnostics does not allow for the fault isolation for which a fault compensation effect occurs. On the other hand, there is a view that application of approaches based on Reiter’s theory allows for the isolation of such faults. The paper shows that these views are not necessarily true. Based on the analysis of a simple system composed of two interconnected tanks, it has been shown that the use of a tri-valued evaluation of residuals allows not only for increasing values of fault distinguishability metrics, but also to take into account the problem of their mutual compensation. In addition, it has been shown that consistency based diagnostics methods developed on the basis of Reiter’s theory may lead to the generation of false diagnoses indicating seemingly compensating faults, even though it is, in fact, impossible due to specific physical limitations of the diagnosed system.