I'll admit I'm fairly new to the ultrasound game so this problem may be elementary to some.
I checked the bearings on a 300hp, 1200rpm, 2300v motor the other day and the dB level would start at around 50 then go up to around 65 then drop down to as low as 30 then come back to the 50 range. Both bearings do it. I had another co-worker check it and he got the same results. I don't think it is a lack of grease but I'm not sure. Out of approx. 500 motors this is the only one I'v heard it on. It started about 2 months ago and I'm thinking of pulling it out of service just to check it.
Any thoughts or suggestions??

Paul,

Is the amplitude variation periodic? For example, does it match slip speed {(1200-Actual speed) x 6 poles}. Say actual speed was 1185 rpm, then (1200-1185)*6 = 90 cpm or 1.5 Hertz with a time period of 0.67 seconds. Have you done any vibration analysis? Have you done any motor current spectrum analysis? Is motor an open frame that is in a dirty environment? Have there been any motor bearing replacements? Why not find out what's wrong before "pulling the motor"?

Walt
w_f_strong (at) msn (dot) com