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Hi All

got an issue with a high 1x on the NDE of a 185KW motor. This motor is used to drive a gearbox which turn rotates 5 rollers which push product through to create animal feed.

Running speed is 1485rpm, used hi-res spectrum to see if I could locate any sidebands but couldn't find anything obvious.

please see attached doc for more details

will post any progress to keep you all updated.

Attachments

Tags: motor, 1x, High Vibration, NDE

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Hi Ralph

So from what I can make out they don't seem like sidebands but they are around 1.8-2.2 CPM apart. Would that reduce the possibility of it being a rotor bar issue ?

Like you mentioned I would have expected to see around 60cpm sidebands for rotorbar issues. 15 slip x 4 poles.

I'm curious as to why I would see such a dramatic difference between the NDE and DE, especially given the layout.

Also why would I have a fairly normal phase at the non drive end between the vertical and horizontal. But then almost in phase on the drive end side ? Just seems rather bizarre.

RM
@Registered Member posted:

Hi Ralph

So from what I can make out they don't seem like sidebands but they are around 1.8-2.2 CPM apart. Would that reduce the possibility of it being a rotor bar issue ?

Like you mentioned I would have expected to see around 60cpm sidebands for rotorbar issues. 15 slip x 4 poles.

I'm curious as to why I would see such a dramatic difference between the NDE and DE, especially given the layout.

Also why would I have a fairly normal phase at the non drive end between the vertical and horizontal. But then almost in phase on the drive end side ? Just seems rather bizarre.

James,

Thanks for the reply.

In your waveform, what are the frequency spacing between "the colored modulation peaks"?

Ralph

Attachments

Images (1)
  • James Waveform
RM

Hello James,

Concerning the waveform questions I had, it is sometimes difficult to put things in understandable words, well. at the least, for me.

Your spectrum appears to need more resolution to separated the sidebands and determine their origin. A 100 Hz Fmax and 6400 or 12,800 line should help. I am basing this on the "wide" empty area to the left of the "marked" 1x peak.

In my attached picture of your waveform plot, can you determine the frequency separation of the "black dot peaks" marked and then find these in the high resolution spectrum? These black dot peaks appear to be modulated themselves by what may be the 4 pole passage of the rotor.

What version of CSI software do you have?

Thanks and Have a Blessed Day,

Ralph

Attachments

Images (2)
  • James waveform Modulation
  • James Motor Spectrum 2
RM
Last edited by Registered Member

Hi Guys, so I went to take a reading today but unfortunately it wasn't running. What I was able to do is get them to run it very briefly so I could take a coast down reading... I've attached the coast down spectrum, it looks like the Coast down shows a range starting from 937cpm to around 1875cpm. This would encompass my 1485 running speed.

The weight of the motor is 1491KG, Can anyone tell me how I would work out how much weight to add to get it away from this range?

Attachments

Images (1)
  • mceclip0
RM
@Registered Member posted:

Hi Guys, so I went to take a reading today but unfortunately it wasn't running. What I was able to do is get them to run it very briefly so I could take a coast down reading... I've attached the coast down spectrum, it looks like the Coast down shows a range starting from 937cpm to around 1875cpm. This would encompass my 1485 running speed.

The weight of the motor is 1491KG, Can anyone tell me how I would work out how much weight to add to get it away from this range?

James,

Impressive spectrum.

But comparing this spectrum to the regular route spectrum, to me, it (the 1,312 cpm amplitude) is not showing under normal running conditions, but that may be (not showing) because the coastdown plot posted doesn't include this frequency (1,311).?????.

This 1,311 cpm peak may be far enough away from the 1485 cpm running speed and only happens on startup and shutdown. as the system goes through a natural frequency and that it (1,311 cpm) does not show in normal running mode.

I would still like to see a spectrum of 200 Hz Fmax and 6400 or 12,800 lines, if possible, so as to separate all the possible sidebands in normal running mode. Unless, it is running close to another natural frequency closer to 1x.

The "wide" noise band next to the left of 1x in your route data may be the part culprit

Just my opinion and I could be totally wrong.

Have a Great Day,

BTW: do you have the waveform belonging to the coastdown spectrum? Have you tried a bump test with the system down to see how "long" the ring-down is from the 1311 cpm frequency?

Ralph

RM
@Registered Member posted:

no you might be totally right it does seem rather odd ! The picture above is the spectrum taken at 1560cpm with 12800 lines ive had to zoom in a little to get a better image. the distance between the sideband is 0.36cpm so a very small difference there!

Thanks James. This is sort of strange for there to be sidebands off the 1x at such a CLOSE distance........

What is the motor driving, a gearbox? and what is the final rpm of the driven part?     If agitator, what is its rpm snd how many blades or paddles?

Ralph

RM

Why use peak hold averages spectrums if you can make waterfall plots, in my opinion 1000hz 400 lines will give you a very fast spectrum and any other harmonics will rise at a resonance "zone" which will give you a better confirmation of resonance

Agree with Ralph, phase at feet and what's this motor driving, motor - gearbox - rollers for a pellet press, how is the feeding "controlled" more material will slow down the motor (increased load) once the motor is free it will spin a little faster, this might look like a weird sidebands when using a averages or a long acquisition time.

Circular waveform of the high resolution spectrum is now always the best choice, try with 10khz and 1600 lines.

It's just my opinion and I could be totally wrong

RM
Last edited by Registered Member

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