Description Imbalance occurs on rotating shafts when the center of rotation and the center of mass do not match. The centrifugal driving force that is generated is proportional to the square of the shaft rotating speed. Therefore, the higher the rotating speed, the better the balance of the rotor should be.
Symptoms Overall value Increased overall vibration amplitude.
Spectrum Peak at 1xRPM with low spectral noise level.
Phase Stable phase readings with a phase change of 90° when moving radially the sensor position by 90°.
Waveform You can see a sine wave.
Severity It depends on the machine type, but in general alarm values range between 3 and 8 mm/s.
Measurement In a machine where there is an imbalance problem we will find an increase in the vibration amplitude in radial measurements, while axial vibration measurements may remain low. In machines with a cantilevered rotor we will also find an increase in the amplitude of the vibration in axial measurements.
Detection Imbalance detection is performed by configuring a frequency band from 0.8x to 1.2x RPM. The monitoring of the measured values in this band gives us the first symptom that the machine can suffer an imbalance.
Correction Imbalance is corrected with a compensating mass at the appropriate location. With a vibration analyzer you can obtain the weight and the angle where to place this compensating mass.