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electricpete, edison123, Franko, Looked again at spectrum with linear scale and the 21,600 is sidebanded with line frequency peaks at very low amplitude. Two on each side of the 21,600 peak are very distinctive then several more that more or less fade into the noise. Thanks. Randy Fizer

electricpete, edison123, Franko, I just set up the spectrum with log scale and 3600cpm fundamental plus harmonics 2 through 8 are present in the spectrum with the 21,600 being the highest. The ninth harmonic is very low and buried in the noise. 10th and 11th harmonics of Fl are present too...

Mcvibe,MJP80, I agree the fault is electrical. And if and when I resolve it, I'll be sure to let you know what I found. The machine drives a mine ventilation fan and must run 24/7 just like a lot of your machines and is difficult to schedule for outage so it may be some time before I can...

Irajak, Thanks for the suggestion. It is one I had not considered. Randy Fizer

Franko, The 21,600 or six time line frequency does not show up on the driven unit. Using an accelerometer for vibration data. The motor is fitted with various tranducers for temperature and vibration data. Will check with electrical department to see if there is any data transmission at this...

Bearing either SKF or FAG. Agree BSF alone is odd. I would think the 11th harmonic of BSF would be very low though I have no experince to back this opinion. Coast down good idea. Hard to shut machine down as it is a mine ventilation fan, but if opportunity comes I will do the coast down to...

Electricpete, Motors drive fans with 16 blades. Motor rotor bar count is 90. Motor does have rolling element bearings one end is a 6324 the other end is a 6234. Time wave form has major peaks that vary in frequency depending on where in the time wave form you make the measurement but all are...

Dave, No VFD's anywhere near these two motors. They are both across the line start. Regards Randy Fizer

I have two 1500 horsepower, 4160 volt, 900 rpm motors running from the same 60 hertz electrical supply. Both are exhibiting increasing peaks at 21,600 cpm. Line frequency and other harmonics of line frequency are present also but not as high and not increasing. Rotor bar peaks and two times...

With an Fmin of 0 cycles per minute and an Fmax of 120,000 cycles per minute and 1600 lines, the FFT bin width is 75 cycles per minute. If there are multiple peaks that fall within a bin, which peak will be shown on the FFT spectrum? If there are other peaks within the bin, how dows one...