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At horizontal direction we measure not only velocity but also acceleration. Two questions:

1. I see a peak around 65000 rpm with sidebands at running speed (1500 rpm) - see illustrations below, I suspect it not a bearings failure but as electrical problem.
2. Here, too, I guess it electrical problem – suddenly the g' of the motor jumping and characterized by high peak around the 160000 – 200000 rpm, also with sidebands but at line frequency relative to motor running speed. For example, motor running speed is 1490 rpm the sidebands will be close to 6000 rpm. Even in case the motor has VFD (motor 3000 rpm 50-60Hz) and the running speed is close to 3600 so the sidebands will be 7200 rpm – see illustration below. Sometimes, it supported at the velocity spectrum by high harmonics at line frequency (6000 rpm).


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  • acceleration
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