I am not sure why no one has replied to your post and questions. Sorry.

Might be because you have already made your report and determinations of the problems.

I do not recall ever making a rotor bar call based on 2xLF, if that is what you seem to be doing. May be that I just have not seen one  (loose or broken rotor bars) with a signature of 2xLF, especially sidebanding off of 1x running speed, one of your pictures seems to show. I have seen plenty of occasions of 2xLF sidebanding off of PPF but they seemingly were not related to rotor bar problems, but more related to off-centered rotor to stator, such as caused by softfoot. But that is from my experience. Maybe I am learning something from your "problem".

I am wondering if the posted data (first screen shot in your post) showing very close to a 4x running speed, is actually related to 1x as the 4th harmonic. Based on the picture , the frequency markers seem to be drifting off, both as a "plus" and a "minus" of the "harmonics", especially on 3x and 5x, if they are really harmonics? Do your cursors setting drift off, as not harmonics as does the frequency lines?

Markers 3x and 5x, are they sidebands off of the tall peak, which is close to 4x or are all the peaks actually 1x and harmonics?

How many "blades" does the pump have? 4?

Thanks and Have a Great Day, Ralph


Why do you think there is a problem in the first place? The vibration amplitudes are very low, so I suspect something else is making you think there is a problem. I don't know anything about your analysis experience so just in case: when you see some characteristic frequency, it's not necessary you deal with some failure.


Quote:"I don't know anything about your analysis experience". Unquote

The following might help us know a little about ANIS VA's analysis experience. Looks like he is a CAT III.

Quote: " ANIS VA

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Describe your interest in maintenance, reliability or asset management

O&M Mechanical Advisor & Vibration analyst CAT III

Will you check your spam folder for our email verification message?

Yes" Unquote.


I would rather not talk about my opinion regarding experience correlated to CAT categories so I will wait if I get the answer to my basic question. By the way I may not be suitable person for this debate because I am CAT 0 (still I find it strange about max. amplitude of 0,45 mm/s causing worries).

Thank you everyone for your feedback,

I did not have a great experience, I consider myself a new in this area (5 years). I have been a member of this forum for almost 4 years and i learned a lot from your comments and recommendations. 
I raised this case because I heard a noise that sounds like an electric noise, it's true that the amplitude is low but. On the one hand, the rotating looseness is remarkable up to 8 X, according to the forum and ISO standard, from 5 X, there is a problem of looseness. I wonder what is the level of alarm admissible in this case?
- 2 xLF is present in all the vertical or horizontal spectrum rather motor/pump. I think that we need to correct the soft-foot.
- I am convinced that the problem of the loose rotor bar  does not exist.
- The pump contains 6 blades, VP is present on the spectrum.
My question is about alarm limits:

rotating looseness and 2xLF?

Thanks in advance.

we should follow the ISO standards or we should setup our limits of alarm?


Thanks BECAR.

This is new installation and i'm trying to setup alarm levels for each machine (more than 200 machines). That's why i'm asking about limits. In this case, it would better to follow ISO standards or to go through another previous history ? 

What do you think?

Thanks in advance


According to my experience, whenever there is a rotating looseness symptom in a motor, its very likely that the bearing housing has excessive clearance or play.

In your case the rotating looseness is of very low amplitude to start a maintenance activity, otherwise I would also have checked for loose rotor on the shaft.

If rotating looseness is present at both pump and motor and and maximum at inboard sides, you need to take a look at your coupling too.

Also, you should be right about cavitation in pump, if cavitation is not present, this type of spectrum is also observed in case of any worn component. 

Let us know whatever you find.

Thanks for this input Ahmed.

in fact, we decide that the next opportunity will check the soft-foot and aligneent as well. at the same time we will take measurement monthy to confirm if theses issue existe. It is new installation, we need to setup our limits alarm for each equipment.

sure i'll share once we do it.


Is the machine new or the instrument new? As BECAR says "the vibrations are very low". You apparently are looking for something/anything in the low-level measurements. I would be very careful about presenting a long list of faults and recommendations to others (boss, operators, and maintenance) without being sure that a real problem/fault is present, especially if machine is new. Once you loose credibility with your results, then others may disregard your future good work!


Hi Walt

From the beginning, I seek the good health of the machine since it is a new installation, maybe because of transport or installation, some faults can appear. it is true that the amplitudes are low but there is looseness is remarkable with noise come from machine. that's why I'm looking for a confirmation or recommanadation.
Finally, we decided to follow the machines without taking any action for it in this moment. and we will setup limit alarms.
sure the next time i'll show you real problem with good clarification and clear spectrum due to i'll install a new software version.

"I seek the good health of the machine since it is a new installation, maybe because of transport or installation, some faults can appear." I completely agree!.

Can you say how the "looseness" is correlated with the audible sound? It is difficult to directly hear 4xSS, especially from a small motor. Perhaps you are hearing a mid-high frequency sound that may be from "rattling" of a loose component? I have seen this with motor air shrouds and vents and coupling guards. A missing wave washer in motor bearing can allow a loose fit that makes noise. Incorrect shaft end-gap can allow shafts to bump together. Is there an identical machine that does not have the same "unusual sound" for data comparison?

I always carry a sound meter with AC signal output in my vibration analyzer case. I can then measure the overall sound level and do spectrum analysis to correlate with vibrations. I also may record the sound on my Sony recorder or phone for later listening and analysis. I also use an ultrasound meter for finding loose components.

I don't want to discourage you from being a good detective (machinery analyst)!


hi Walt.

Maybe I did not take the right example, besides I have a problem with updating the software that's why I made this report manually from the analyzer, threfore my diagnostic is not accurate . but, i think that i collect more recommendations for the next time I will take care on it.
for the ultranonic device, I used a lot of times before but unfortunately in this new project, we have not yet bought it.

Sure, I'll take care up next.


Assume pole pass frequency: 1500-1462X4=152 cpm or 2.53 hz pole pass frequency. Is the motor driven by VFD or speed drive

If I read your plots correctly the vibration level @ 1X rpm is equal to .001 in/sec in vertical direction, then the axial direction 6 m/s2 around 1200 hz? This is like 2.0 in/sec?

The link below is a mobius calculator, I input 1462 cpm with .03 mm/sec rms

Examples, The first plot 24000 cpm or 400 hz 6400 lines 2 avg 50% overlap hanning shows multiple turning speed harmonics with multiple pole pass frequency sidebands around each running speed harmonic 


The below plot zooms in to show sidebands 1200 rpm machine


3600 rpm machine also showing pole pass sidebands around turning speed harmonics and yes waveforms show modulation in both examples


Recommend you take low frequency high resolution data to ensure you have the correct data to make a definitive call on the problem

Bad rotors in a motor will exhibit loud beating noise, motor will vibrate because one rotor bar starts to move outward causing imbalance, motor will run hot, motor will loose horsepower/KW, motor amps will constantly swing even though the load is steady, plus vibration signatures. Be cautious about calling bad rotor bars using rotor bar passing frequency, it has been my experience that pole pass is a better identifier of bad rotor bars. 99% of all motors over 25 years that I monitor exhibit 2xLF around rotor bar passing frequency without rotor bar issues. Some motors are built with less quality than others, some rotor bar and stator slot combinations are noisy, hollow bases amplify motor noise, have seen bad gear coupling create similar vibration as to what you have posted

Motor Circuit Evaluation can be done while motor is under 70% load or greater, this test also identifies if there is a suspected problem with motor rotor bars.




Photos (3)

I agree with Walt.

What in is this world is Lisa Alix talking about?

From the info on the registration profile, it appears the person, be it man or woman, is in the auto transport business, or something other than vibration analysis.

I bet, who ever it is, doesn't even know what "rotor bars" are.

Quote from the person's profile: "We provide car transport, vehicle transport, auto transport, car shipping, auto shipping, vehicle shipping services. We will provide safe and secure given your car at your destination without a problem, and we are a top-listed forum for the help people for other detail visit our site."

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