Combining qualitative model-based diagnosis and observation within fault-tolerant systems

The increasing importance of fault-tolerant technical processes leads to ne w model-based approaches. In the approach proposed here, the effects of fau lts are decreased by additional control commands supplied by a fault-tolera nce algorithm. This algorithm combines qualitative model-based diagnosis an d observation. The main idea is to reach the non-faulty output and non-faul ty state as accurately as possible even in the presence of faults. The sign als and faults are described qualitatively by discrete values, and their re lations are formalized by an automaton. This automaton is used in diagnosis to identify faults, in observation to identify the present state, and in s imulation to identify the correct output and state. A correction mechanism determines an additional control command which would have led to correct be haviour at the current time point and applies it to the process at the foll owing time point. The approach is illustrated by an example of chemical pro cess engineering.