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VibraMac

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Reply with quote  #1 
Send a spectrum with an amplitude scaling as 'mg'.  I assume this is milli-g's (0.001 g).
Is this sometime new!!!!  What happened to log scaling.

Series of harmonic amplitude peaks between 30 to 45 (I assume 0.030g and 0.045g) on a full scale of 50 and suggesting bearing looseness!! 

If this is a valid amplitude scale is there any international spec quoting this type of scaling?
spciesla

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Reply with quote  #2 
Might as well be milligrams!
OLi

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Reply with quote  #3 
Or it is just the software guy on the loose or rather the graphics library he use.
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John from PA

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Reply with quote  #4 
Quote:
Originally Posted by VibraMac
What happened to log scaling.


Is it mg ("milli" g) or µg ("micro" g)?  1 µg (rms) is the reference for acceleration expressed in decibels (AdB).

I personally never cared for log scaling except for a few select instances (acoustics, side band analysis, etc.)  Every time you showed a customer inspector a log scale of a casing signal off a gearbox they wanted an explanation for every peak, regardless of amplitude.
JuddJones

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Reply with quote  #5 
IFM uses Milli G for all of their acceleration units. I use IFM quite a bit as it was installed on equipment in our mill when I began this crazy vibration stuff. It took me awhile to get used to the milli G...
VibraMac

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Reply with quote  #6 
Thanks for that..So I'm correct in that mg is milli-g.  Are there any international standards with this type of amplitude?

Not familar with IFM, please elaborate.  Much appreciated. 
John from PA

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Reply with quote  #7 
I think the IFM that "Big J" is referring to is a German firm.  The link, filtered to South Africa content, is http://www.ifm.com/ifmza/web/home.htm
MarkL

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Reply with quote  #8 
Seen an online monitoring setup in IFm recently and they measure mg instead of G and its a bit of a head-wreck, 
VibraMac

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Reply with quote  #9 
Someone help me here.  I have not monitored/analysed roller element bearings for many years.  My last 'hands on' was with the IRD 820 (I think) in the late 80's.  Why do we need to know the state of the bearing in mg.  Surely concern needs to be raised once it starts to generate the fundamental bearing frequencies.  I for one would not suggest removing bearings with such low amplitude levels that are measured in mg. Lets get some operational life from the bearing of concern.  Mention its to the client and monitor carefully.

If I remember the 820 had sometime like 'spike energy' which had to be used with the standard stinger (9'').  Never trusted it particular on pump (cavitiation) and always took the above approach.
OLi

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Reply with quote  #10 
I thought I saw that somewhere, we did setup alarm and monitoring settings on a couple of IFM systems on hydroplants. It is just a not so normal prefix scaling so it is a measurement in G just that the scale is in a 1/1000 G or milli G just to confuse you in to reading the manual maybe. So I have yet to see a bearing damage increasing the scale and at least one of them it is not likely as it does not have antifriction bearings. So it is normal procedure I guess, follow the trend regardless of the scaling.
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JuddJones

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Reply with quote  #11 
I believe IFM uses MG because there system takes the BPOR, BPIR, BSF x 2, and adds it together and plots its highest value in a history at intervals of your choosing. If I remember correctly the software creates a bandpass filter for the FFT that has a narrow envelope 2% on each side of the forcing frequency of those bearing defects and tracks them continuously , then plots the highest values of those summed values and stamps them in the history at your chosen interval (you can also log the average of the value over the set time). Because these are only the fault frequencies the values are rather low (see the chart posted below of there recommended damage levels). The other picture is a view of what a failing bearing in this history looks like.

IMG_2817.JPG

2017-04-30 07_20_54-LL Gang bearing change resized.png 

VibraMac

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Reply with quote  #12 
Thanks Big J. The acceleraton table atleast gives something to work with.

 Did you by chance seen the bearing's condition in question?
JuddJones

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Reply with quote  #13 
The answer to that would question would always be yes, however this piece of equipment belongs to my partner, I just stole the picture. I am not sure if he cut that bearing open or not.
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