Patent US 4,989,159

Method of monitoring the operational state of a machine, particularly one having two mutually co-acting rotating machine parts operating at different revolutionary rates. Sensed vibration spectra are compared with theoretically calculated spectra and the peaks in the respective spectra are mutually matched. Each match or assignation is alloted an adjustment weight, which is specific for a given machine part and which increases with the amplitude of the peak and decreases with the frequency distance between the peaks. The adjustment weights are summed into weights which are attributable to the respective machine part. The part weights form weight vectors, and a reference class is formed on the basis of a plurality of weight vectors obtained during normal operation. Each new weight vector is compared with the reference class, and it is then determined whether the difference exceeds a predetermined statistical spread value.