A quick reference for vibration spectra of rotor imbalance including Static Imbalance, Couple Imbalance, Dynamic Imbalance and Overhung Imbalance. It covers typical vibration spectrum shape and important tips of each imbalance type.

1. Static&Imbalance-
• Also%known%as%forced%imbalance%2
• Weight%distribution%axis%parallels%the%rotational%axis.2
• Occurs%when%a%heavy%spot%is%located%at%the%mid>point%between%the%bearings.%2
• More%common%in%rotors%that%are%short%compared%to%diameter.%2
2
Couple&Imbalance-
• 180°%out>of>phase%on%same%shaft2
• 1X%always%present%and%dominates%the%spectrum%2
• Amplitude%varies%with%square%speed.2
• Weight%distribution%axis%intersect%the%rotational%axis2
• Correction%requires%the%balance%weights%in%at%least%2%planes.%2
2
Dynamic&Imbalance-
• Also%known%as%quasi>static%imbalance%2
• Most%common%imbalance2
• Occurs%when%the%rotational%axis%and%the%weight%distribution%axis%do%not%intersect%at%all.%2
• A%combination%of%static%and%couple%imbalances%2
Overhung%Imbalance-
• 1X%radial%and%axial%vibrations2
• Radial%signals%are%because%of%bending%effects2
• Axial%readings%might%be%unsteady2
1X:$$$Radial$
RPM$
Amplitude$$
1X:$$$Radial$
RPM$
Amplitude$$
1X:$$$Axial$&$Radial$
RPM$
Amplitude$$
1X:$$$Radial$
RPM$
Amplitude$$
www.mo7onics.com$$$$$$$$info@mo7onics.com$
$