I have a motor with 1, 2, and 3 times RBPF skirted by 2x Fl (7200cpm/120Hz). Every time I have encountered this problem prior to this 2x RBPF has been elevated accompanied by 2x Fl, but I have a 3x RBPF in the mix. The 2x RBPF is not elevated to a magnitude of concern as yet. However, the 2x Fl side banding is larger than 50% of the 2 x RBPF signatures. Haven’t found Fs or Fp around 1x fundamental or multiplies of. Can anyone be of assistance on this? Thanks Jerry Bryant

First make sure you have enough resolution to see the sidebands around 1x spaced at Fs or Fp. (For example: Fmax=12000cpm and 3200LOR)

JB,
Is this a Toshiba motor? I ask because I have seen multiples of RBPF with no rotor damage. I believe they just have a weaker housing structure. It is usually indicative of rotor deflection in the airgap (dyanamic airgap). Check the vibration into the motor from the driven equipment.

No Ron it is a US Electric
Thanks for the come back.

Thanks Elias I have 1600 LOR @ present and looks as if side bands of Fp and Fs are riding 1x TS and fundements but am going to 3200 LOR to confirm

JB

Have you had a chance to run this motor uncoupled? And what about soft foot, anything there?

Also Elias had a good suggestion. I had the similar thing happen to me recently, and getting that higher resolution really makes the difference, and can differentiate and separate those peaks. Also zoom in on your spectrums, and see if you have any pole pass freq between the .03-2.0 htz range. That helped me find my uneven air gap problems in my last motor I pulled. Those low frequency spectrums at a higher resolution looks just like the Tech Associate Wall chart.