Method and apparatus for measuring rotor unbalance

1. A method for measuring rotor unbalance, comprising:

rotating a rotor about an axis at a range of rotating speeds;

generating a reference signal indicative of the instantaneous rotational frequency of the rotor;

detecting the vibration of the rotor while the rotator is rotating, and generating a vibration signal;

filtering the vibration signal, using the reference signal, to provide a synchronous vibration signal having a frequency equal to the instantaneous rotational frequency of the rotor;

recording a vibration vector, the vibration vector comprising amplitude and phase values for the synchronous vibration signal; and

measuring rotor unbalance based upon the vibration vector.

2. The method of claim 1 , further comprising:

recording a plurality of vibration vectors, each vector corresponding to one of a plurality of revolutions of the rotor; and

determining an average vibration vector from the plurality of recorded vectors.

3. The method of claim 2 , wherein determining an average vibration vector comprises:

calculating x and y components for each recorded vector, wherein the x-component of each vector comprises the amplitude of the vector multi the cosine of the vector phase angle, and wherein the y-component of each vector comprises the amplitude of the vector multiplied by the sine of the vector phase angle;

determining the sums of the x and y components of the recorded vectors to produce x and y component sums, X and Y;

determining an average amplitude value from the x and y component sums, where the average amplitude, A(avg.), is 1/n*(X2+Y2)½, where n is the number of recorded vectors; and

determining an average vector phase angle value from the x and y component sums, where the average vector phase angle is cos−1 (X/[X2+Y2]½), where Y $ 0, and 2B−cos−1(X/[X2+Y2]½), where Y<0.

4. The method of claim 2 , wherein at least about 100 vectors are recorded.

5. The method of claim 1 , further comprising determining a location for and amount of correction weights to be added to or removed from the rotor to reduce the detected rotor unbalance.

6. The method of claim 1 , wherein measuring rotor unbalance comprises determining the existence and location of a rotor anomaly.

7. The method of claim 6 , wherein the anomaly comprises a crack.

8. An apparatus for measuring rotor unbalance, comprising:

a vibration sensor which measures the vibration of the rotor while the rotor is rotating, and generates a vibration signal;

a speed sensor which generates a reference signal indicative of the instantaneous rotational frequency of the rotor;

a filter which filters the vibration signal, using the reference signal, to provide a synchronous vibration signal having a frequency equal to the instantaneous rotational frequency of the rotor;

a detector which measures a vibration vector, the vibration vector comprising amplitude and phase values for the synchronous vibration signal; and

a processor which records the vibration vector and measures rotor unbalance based upon the recorded vibration vector.

9. The system of claim 8 , wherein the dectector measures a plurality of vibration vectors, each vector corresponding to one of a plurality of revolutions of the rotor; and wherein the processor determines an average vibration vector from the plurality of recorded vectors.

10. The system of claim 9 , wherein the processor determines the average vibration vector by:

calculating x and y components for each recorded vector, wherein the x-component of each vector comprises the amplitude of the vector multiplied by the cosine of the vector phase angle, and wherein the y-component of each vector comprises the amplitude of the vector multiplied by the sine of the vector phase angle;

determining the sums of the x and y components of the recorded vectors to produce x and y component sums, X and Y;

determining an average amplitude value from the x and y component sums, where the average amplitude, A(avg.), is 1/n* (X2+Y2)½, where n is the number of recorded vectors; and

determining an average vector phase angle value from the x and y component sums, where the average vector phase angle is cos−1(X/[X2+Y2]½), where Y $ 0, and 2B−cos−1(X/[X2+Y2]½), where Y<0.

11. The system of claim 9 , wherein the detector measures and records at least about 100 vectors.

12. The system of claim 8 , wherein the processor determines a location for and amount of correction weights to be added to or removed from the rotor to reduce the detected rotor unbalance.

13. The system of claim 8 , wherein the processor measures rotor unbalance by determining the existence and location of a rotor anomaly.

14. The system of claim 13 , wherein the anomaly comprises a crack.