A Modified Approach to Observer-based Fault Detection

This paper presents a practical and useful modification to the observer-based fault detection technique so that the fault indicator is independent of the observer gain. To this end, the notion of "Total Measurable Fault Information Residual" (ToMFIR) is utilized. It is shown that the conventional fault indicator used in observer-based approaches (the observer output residual), being a function of the observer gain, is not totally reliable for the detection of small faults. We present a simple modification that results in a fault indicator which approaches the ToMFIR in the limit, if the fault function approaches a constant. A DC motor example is simulated in Matlab environment to illustrate the effectiveness of the modified observer residual as a fault indicator.