Messrs. Forum:

Good evening, I will greatly appreciate a query regarding the attached SKF (Acceleration Enveloping (gE) Alarm), there is confusion about it, in vita that literature has been found where it says that the values of Enveloping Severity in this table are Global Values (RMS) of gE and there are other literatures where it says that these values of Enveloping Severity of the table correspond to values Peak to Peak of gE.

Please your technical support.

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Original Post

Very good question! I am not a big fan of the ˝table˝ envelope analysis (I don't use it) but I know this SKF enveloping alarm table and I know the confusion about it. Can you provide some source, where you have seen that the values in the table should be RMS values? As the table comes from SKF, I think you should accept the SKF literature only.

But here is one thing that bothers me. Per my experience the values in the table should be closer to RMS than P-P. That is why I never used it for reference.

There is one other tricky thing. Imagine you measure the same bearing with different equipment at the same time. RMS envelope value will not be the same at all equipment providers.   

jorgeluis-2000 posted:

Messrs. Forum:

Good evening, I will greatly appreciate a query regarding the attached SKF (Acceleration Enveloping (gE) Alarm), there is confusion about it, in vita that literature has been found where it says that the values of Enveloping Severity in this table are Global Values (RMS) of gE and there are other literatures where it says that these values of Enveloping Severity of the table correspond to values Peak to Peak of gE.

Please your technical support.

Hi

Can you attach the literature where the gE values are said to be in RMS.

SKF table is in pk-pk.

Thanks

Akhil

 

Akhil Rathore posted:

That literature is still awaited...!!!

Meanwhile you can see this Webinar recording..watch it till the end.

http://hiresmedia.skf.com/camp...sentation_html5.html

 

 

Good afternoon, attached an extract of a Thesis that I found on the Internet (in Spanish), in the Envelope spectrum says Ge peak to peak but in the spectrum note says global value 3,814 gE RMS and this has created confusion, it is assumed that the global value should I say 3,814 gE peak to peak or 3,814 gE RMS ?.
I will appreciate your comments.

Greetings.

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Again as I said RMS is of little use with gE, always use peak or if possible true peak.

the reason for this is impacting get avergaed out and are of little use. 

Please find from skf technical newsletter.

Quote-

gE why not to average.

Fast Fourier Transform (FFT) relies on a signal consistently repeating itself with time and averaging is used for standard Condition monitoring as it allows the data to become more statistically correct. However the process of averaging when applied to gE readings actually damages the data – Why? Bearing defect frequencies can be looked at as random signals in our data block as they do not happen synchronously with other rotational characteristics. Averaging exponentially reduces random frequencies with each average so we are potentially exponentially removing the bearing fault frequencies with every average applied.

One long FFT is much better than several quick overlap averages. In addition to this, the averaging process uses overlapping. This process allows us to reuse a percentage of the last signal block as the first corresponding percentage the signal in the second data block speeding up data acquisition 50% has become the standard overlap when averaging data. This reuse of the signal can make the bearing signals appear even more random and removed in the average process. 

Rms V Peak/True Peak.

The choice of amplitude descriptor (detection type) also has a large effect on the quality of the data. If we look at a typical data block in the time domain (picture below), we can see some tall peaks due to short duration impacts - potentially bearing defects? If we use an RMS amplitude descriptor, then we sum the individual values and reduce the measured level to a much lower calculated value. Individual peaks would have to grow massively before they have an impact on the RMS value. If we select to use Peak or Peak-to-Peak then we are still not capturing the data correctly, as these two descriptors are calculated from the RMS value (Pk =1.414* RMS) (Pk-Pk = 2 *Peak) The correct way to look at this data is with a TRUE Peak detector as used in the Microlog

 

 

That’s true but the document is aimed at the technologies initial basic use.

The Lubrication capability was a field engineers discovery in later years. I

I myself use gE for Lubrication purposes in my field work but still have it setup to detect in peak.

i don’t speak Spanish so cannot decipher what that document is outlining. 

 

jorgeluis-2000 posted:
Good afternoon, attached an extract of a Thesis that I found on the Internet (in Spanish), in the Envelope spectrum says Ge peak to peak but in the spectrum note says global value 3,814 gE RMS and this has created confusion, it is assumed that the global value should I say 3,814 gE peak to peak or 3,814 gE RMS ?.
I will appreciate your comments.

Greetings.

As per the spectrum you've attached the gE value recorded is 3.814 & the Y axis shows the measurement in Pk-Pk. I dont know why he wrote gE RMS below the spectrum when he measured it in pk-pk. Also if he mathematically converts 3.814 pk-pk to RMS the value will change. So I would personally consider the comment below the spectrum a Typo error mentioning it in RMS.

Thanks

Akhil

This is as usually not a digital choice, right or wrong. I read a old SKF research report long time ago and in short, if you use accel and peak you will have early detection and a jumpy trend, if you are a different person and look for later detection and a stable trend, use velocity and RMS like soon 300+ Chinese do. So make your choice or not, for route collection I use both as I am that kind of person wanting the cake and eat it.....

Becar posted:

@DBTCMP

The SKF newsletter doesn't consider that some people (not me) use Envelope / Peakvue / Demudulation for lubrication issues also. In that case the RMS value is a lot more important than P-P. 

 
Sir @DBTCMP:
Good afternoon, please attach the SKF newsletter, I will be extremely grateful.
Best regards.
 
OLI posted:

This is as usually not a digital choice, right or wrong. I read a old SKF research report long time ago and in short, if you use accel and peak you will have early detection and a jumpy trend, if you are a different person and look for later detection and a stable trend, use velocity and RMS like soon 300+ Chinese do. So make your choice or not, for route collection I use both as I am that kind of person wanting the cake and eat it.....

Mr. Oli:

Good afternoon, I will be extremely grateful to attach the SKF technical report that you mention, it will be very helpful.

Best regards.

Walt Strong posted:

Mr. From:

Good morning, I would really appreciate it if I had the article SKF Acceleration Enveloping and Other Bearing Defect Detection Methods.pdf? please share it.

Best regards

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