Wavelet Transform Based Methodology for Detection and Characterization of Multiple Oscillations in Nonstationary Variables

Diagnosing the root cause of a propagated oscillation in the operation requires detection of all process variables that are oscillating with similar frequencies followed by application of an appropriate root cause diagnosis procedure. Oscillations in chemical processes are usually caused by controller tuning, valve problems, or external oscillatory disturbances. There are several methods proposed in literature for root cause diagnosis of oscillations within the system. However, most of the methodologies can only work for a specific type of oscillation. For example, the methodologies based on quantifying the nonlinearity of variables can help with root cause diagnosis of a valve-induced oscillation but cannot help if the oscillation actually has occurred due to aggressive controller tuning or due to an external oscillatory disturbance. Therefore, before trying to find out which loop within the system has caused the oscillation, it is important to categorize the oscillation meaning to learn if the oscillati...