Verification of magnetic balance for magnetically levitated impeller

1. A method of verifying magnetic balance of a magnetically-levitated impeller of a centrifugal pump, wherein the pump includes a pump housing having levitation magnets for providing a levitation field, wherein the impeller includes embedded magnets, wherein the pump housing defines a chamber containing the impeller, and wherein the impeller is axially movable between first and second sides of the chamber, the method comprising the steps of:

mounting the centrifugal pump on an acceleration fixture while the impeller is held against a predetermined one of the first and second sides by the levitation magnets;

determining a desired retention force for holding the impeller against the predetermined side that corresponds to a desired balance force to be applied to the impeller when levitated away from the predetermined side;

applying a first predetermined acceleration to the acceleration fixture that corresponds to a force of acceleration on the impeller less than the retention force;

determining whether the impeller detached from the predetermined side, wherein an unbalanced condition is detected if the impeller has detached;

with the impeller held against the predetermined side, applying a second predetermined acceleration to the acceleration fixture that corresponds to a force of acceleration on the impeller greater than the retention force; and

determining whether the impeller detached from the predetermined side, wherein an unbalanced condition is detected if the impeller did not detach.

2. The method of claim 1 wherein the desired retention force is determined as a range, and wherein the first and second predetermined accelerations correspond to forces of acceleration bracketing the range.

3. The method of claim 1 further comprising a repeat of the determining and applying steps with the impeller held against the other one of the first and second sides.

4. The method of claim 1 further comprising the steps of:

weighing the impeller; and

determining the first and second predetermined accelerations in response to a value of F R /m imp , where F R is the retention force and m imp is the mass of the impeller.

5. The method of claim 4 wherein the first and second predetermined accelerations are applied vertically, and wherein the step of determining the first and second predetermined accelerations is compensated for gravity.

6. A method of verifying magnetic balance of a magnetically-levitated impeller of a centrifugal pump, wherein the pump includes a pump housing having levitation magnets for providing a levitation field, wherein the impeller includes embedded magnets, wherein the pump housing defines a chamber containing the impeller, and wherein the impeller is axially movable between first and second sides of the chamber, the method comprising the steps of:

mounting the centrifugal pump on an acceleration fixture while the impeller is held against a predetermined one of the first and second sides by the levitation magnets;

applying a plurality of predetermined accelerations to the acceleration fixture to exert a plurality of different forces of acceleration on the impeller;

determining whether the impeller detaches from the predetermined side as a result of each different force of acceleration to identify adjacent forces for which a transition occurs between detaching and not detaching;

comparing the transition with a desired retention force to determine whether the pump achieves magnetic balance.

7. The method of claim 6 wherein the desired retention force is proportional to a desired balance force to be applied to the impeller when levitated away from the predetermined side.

8. The method of claim 6 wherein the desired retention force is proportional to a retention force measured with the impeller held against the other one of the first and second sides.