An accurate method to obtain magnitude and phase of rotor unbalance signal

摘要

It is very improtant to balance rotor in-situ for gas turbines and power engines. Rotor balancing is usually carried out through vibration phase and magnitude of rotors. Normally vibration phase and magnitude are obtained from FFT of the vibration picked at bearing supports. Because leakage, aliasing and grid leaking exist in FFT, the precision of phase and magnitude especially vibration phase is not high enough which will decline balancing efectiveness. This paper presents a practical method to obtain vibration phase and magnitude accurately in-situ. By FFT theory, if sampling by an integer factor via rotary speed while taking balance, leakage, aliasing and grid leak will not exist in FFT calculation and accurate phase and magnitude can be obtained. Tracking sampling via rotor rotary speed satisfies the demand of sampling by an integer factor. To generate tracking pulses, PLL )Phase Lock Loop) technique is used to track the change of rotary speed. If rotary speed dose not change very swiftly, the precision of phase and magnitude could be quite high inspite of rotary speed waving. Beside theoretical analysis, experimental results and comparison between free sampling and tracking sampling are also given.