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MarkL

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Just been on the other forum and seen an old topic on a vertical motor with VFD which had a high peak and Ron Brook made a comment along the lines of 'VFD controlled motors and high acceleration readings go hand in hand'
 I am curious what is the process/methodology to this?  And I would be grateful if it can be explained to a non-electrical noob. I have recently started a contract in a new plastic extrusions plant with loads of VFD (Both DC and AC) controlled motors and notice a lot of higher than expected...(well from my limited experience in other factories I survey) acceleration readings.

I work in peak acceleration and have 1st alarm levels set at 0.8g(Alert) and 2nd alarm(Warning) set at 1.5g (these were levels passed onto me by predecessor before someone asks. Motors are almost all 4 poles 1450rpm 50hz supply.

I would love some Input by Mr Brook himself (if he see's this) but of course its open to anyone who can answer the question or add to my inquiry.

Many thanks
Ron Brook

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Mark,
The higher acceleration levels in motors on VFDs are as result of the high frequency switching of the voltages fed from the VFD.  These always result in broad band acceleration time waveform data.  Bad bearings due to EDM damage will have period spiking in the time waveforms as well as multiple harmonics of the BPFO or BPFI in the velocity data.  I will see if I can post some examples after I return to my office next week.
Regards,
Ron Brook
MarkL

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Cheer's Ron,
I appreciate your response, and that makes perfect sense to me, I have two particular problem children at the plant both have had repeated emd issues, and I did notice the acc twf was particularly spiky in comparison to others.
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