Unbalance Definition
Unbalance occurs when the mass centerline does not coincide with the shaft centerline. It is also defined as the distance between rotation center and mass center.
3 types of unbalance ; Force, Couple and Dynamic .
Unbalance is always indicated by high vibration at 1X RPM of the unbalanced part (but,
vibration at 1X RPM is not always unbalance).
Normally, this 1X RPM peak will dominate
the spectrum.
In-situ Balancing
In-situ balancing eliminate the Imbalance/Unbalance mass of a rotor. Balancing spin the rotor to detect the center of mass through vibration sensors.
These vibration sensors are usually accelerometers.