A new criterion for detecting oscillations in control loops

We suggest a new criterion for automatically detecting whether a control loop has oscillative behavior or not. The criterion only uses data collected in closed loop, and is model free, i.e. no process model is needed and no experiments are required. It does not rely on frequency analysis. The criterion has been evaluated on a large set of data collected from many different loops at a paper mill. One of its strengths is that it detects oscillations containing several frequencies, irregular oscillations, and asymmetric oscillations.