Journal Article

Detection and Diagnosis of Oscillation in Control Loops

N. F. Thornhill, Tore Hägglund


Previous work presented a real-time algorithm for detection of oscillations in PI and PID feedback control loops. This paper examines further opportunities for oscillation detection in the off-line analysis of ensembles of data from control loops. Its use with measurements from routine operations is emphasised. The paper presents operational signatures that indicate the cause of an oscillation. Typically, a full diagnosis requires a special test for which the loop is taken out of routine operation. The signatures lead to recommendations about which special test is most appropriate. They therefore reduce the time spent in trouble-shooting by guiding the choice of thest.


Control loop, fault diagnosis, performance analysis, power spectra, valve friction

Control Engineering Practice, 5:10, pp. 1343–1354,1997.