When unbalance has been identified with the help of FFT vibration analyzer, then the correction is straightforward. Weight has to be either added or removed from the rotating equipment.
Unbalance is measured and reported in two ways. One is a measure of the effect of the vibration and the other is a measure of the heavy spot. The vibration measure is used in fieldwork and embodies the speed characteristics of centrifugal force effects. In field balancing rotors runs at their own operating speed, with minimum disassembly. A basic requirement in place balancing is that the rotor has to be accessible to make corrections.
The vibration level measured at the 1*rpm is used as an indicator of the amount of unbalance. The location is determined by measuring the phase. Phase, is measured by an indicator in the instrument, triggered by a photocell.
The common language definition of unbalance is the unequal distribution of the weight of a rotor about its rotating centerline.
The Formal definition of unbalance is that condition which exists in a rotor when vibratory force or motion is imparted to its bearings as a result of centrifugal forces.
The technique of field balancing offers some distinct advantages as:
Balancing is performed on the complete assembled machine and hence compensates the assembly tolerances.
The cost and time to dismantle the machine is saved.
The possibility of damage to rotor in dismantling and carrying it to balancing station is eliminated.
The effects of temperature, pressure, distortion and other environmental influences can be incorporated.