A Fuzzy-logic System for Detecting Oscillations in Control Loops

The automatic detection of oscillations in control loops is essential for effective performance monitoring. However, the methods known from the literature are often sensitive to normal system responses such as step changes in the reference or the rejection of disturbances. Therefore, a novel criterion is proposed in this paper. It uses on-line spectral analysis over a moving window and subsequent fuzzy decision making based on the magnitude and duration of oscillations as criteria. An offline adaptation mechanism is available to tune the system with the help of data and expert knowledge. The usefulness of this criterion has been demonstrated by using real-time data from dissolved oxygen and pH control loops in a fermentation process.