Two Minute Tips  

Motor Magnetic Center

Noah Bethel | Vice President-Product Development, PdMA Corporation

Running a motor uncoupled will pull the motor rotor into a magnetic center, often marked on the shaft to ensure that the rotor is lined up on the magnetic center when it is coupled to the load. Axial misalignment of a coupling can occur if the coupling ends are not close enough when they are bolted together resulting in pulling the rotor out of magnetic center. When this happens, the rotor is constantly trying to pull itself through axial thrusting back to magnetic center and could result in uneven and or excessive bearing wear. Using the Emax technology you can evaluate the 5th harmonic peak as an indicator of this magnetic center offset and axial movement. Normally the 5th harmonic is a single clean peak in the current spectrum. However, if axial thrusting is occurring the 5th harmonic will split into two smeared peaks.

To see an example and hear a case study on a suspect magnetic center offset visit the PdMA YouTube Channel at:

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3 years ago

If the motor has deep groove antifriction bearings, then how can we identify the magnetic center?

2 years ago
Reply to  Rajesh

If the motor has AF bearings, it would not have a magnetic center.

1 year ago
Reply to  Rajesh

Very good question, I am facing the same issue.

Pinak Vadher
Pinak Vadher
1 year ago

During a decouple trail, what shaft position should a motor with both journal bearing indicate? Will the shaft beacome steady at magnetic centre mark or keep axially floating?

About the Author

Noah Bethel Vice President-Product Development, PdMA Corporation

Noah has over twenty-five years of broad operations and electrical systems maintenance experience in industrial, commercial, and military settings ranging from nuclear submarines to world class amusement parks. His experience includes high and low voltage, AC and DC, power generation, power distribution, motors, and motor controllers. Noah is currently in charge of product development for new and existing PdM technology at PdMA Corporation.

Noah is a graduate of the University of the State of New York and the Naval Nuclear Power School and Training Unit. He is a Certified Maintenance Reliability Professional, with field experience in motor circuit analysis, current signature, power analysis, thermography, vibration analysis, oil analysis and ultrasonic testing.