Initial experience in applying qualitative reasoning to process control

The application of qualitative reasoning methods to the control of single-input-single-output systems, using the two-coupled-tanks system as an example, is considered. The basic issues are discussed, and the benefits of combining qualitative and domain-specific quantitative knowledge is demonstrated. it is shown that a combination of simple qualitative modeling and domain-specific quantitative knowledge can mitigate the drawbacks of the basic qualitative controller. The identification of the significant quantitative parameters and their values requires some experimentation. For the two-tanks problem the trend interval and the practical rate of change of levels have been identified as important parameters in addition to the sample-action interval and the voltage increment. The resulting performance is comparable to that of a proportional-integral-derivative (PID) controller