Farahani,

I am no electrical whiz, but looks like you either have a bad mechanical looseness problem or a bad electrical problem, if this thing is running uncoupled.
Have you strobed the motor to see what the shaft might be doing?

What does the waveform show?

Dear Ralph
Unfortunately, until now we have not stroboscope and also our data collector doesn,t show TWF. I want to use Oscilloscope for TWF but our accelerometer haven't required sensitivity and I have to prepare a new one.
Regards.

Having several run speed harmonics with low 1x and 2x as result of severe misalignment have been documented in vibration literature (for example, CSI) although without any solid theoretical back up.

What is not clear in the presented case is interpretation of 3.7hz spaced sidebands. Does not look like it is PPF. Although they are gone after alignment, it is interesting to research their origins.

Am I reading the last three spectrums on page 1 dated January 22, 2007 wrong? Are they from an entirely different motor than are the first set of spectrums dated January 14, 2007 at the beginning on the thread?