Abstract: Automatic detection of excessive oscillations in feedback control loops of a completely general nature can be achieved by generating an autocorrelation function of the controlled variable or control error in the control loop. From the pattern of the autocorrelation, a decay ratio which is a function of the depth of the first minimum and height of the first maximum of the oscillation in the autocorrelation function can be generated as a measure of the oscillation in the control loop. When the decay ratio exceeds a predetermined threshold, an alarm or report can be provided indicating that an excessive oscillation has occurred and to what degree. The source of the oscillation, that is whether it is within the monitored control loop or from a source external to the control loop can then be determined and the necessary remedy applied including a step input signal to the final control element in the control loop.