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Walt Strong

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Reply with quote  #16 
I hope that the OP (Curran99) will provide some feedback response to make this discussion worthwhile.

Walt
      
John from PA

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Reply with quote  #17 
Walt, not sure why but I don't see anything in the prior post immediately above this one.  I think you are using that secret ink again.  [smile]  However, if I do a reply with quote it appears as if your content is as below:

Quote:
Originally Posted by Walt Strong

I hope that the OP (Curran99) will provide some feedback response to make this discussion worthwhile.

Walt


I do recall that Curran99 made some comment about getting on a plane (2 days ago) so perhaps he is still involved with a project or traveling.
Curran919

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Reply with quote  #18 
It'll be worthwhile and appreciated! I was just working two weekends in a row with some tight deadlines and vacation begins tomorrow! I'll go through everything and give it's due attention :-)
Walt Strong

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Reply with quote  #19 
John, once in a while I do use disappearing ink! All I can say is that what you captured in your post is what I said, and fortunately the OP saw it.

Regards,
Walt
John from PA

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Reply with quote  #20 
Quote:
Originally Posted by Walt Strong
John, once in a while I do use disappearing ink! All I can say is that what you captured in your post is what I said, and fortunately the OP saw it.

Regards,
Walt


I wonder if you inadvertently selected white as your text color?  

text color.jpg 

OLi

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Reply with quote  #21 
You need a Torsion F/V converter to read those invisible writings?
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Curran919

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Reply with quote  #22 
Back from vacation now, but I was thinking about you guys the whole time. [wink]

Quote:
The frequency range that is shown does not even cover +/- 1xSS, and certainly not the +/- 5xSS expected from vane pass pulsation. I suggest using wider frequency range and Log amplitude scale to see if there is anything besides noise.


I don't really understand what you mean, Walt. The BPF vs. tooth carrier frequency is always going to be at a ratio of 5:32. That is fixed regardless of pump speed or sampling rate. Sampling rate is at 51.2kHz. More below.

Quote:
you could also use straingauges and telemetry.


Aye Olov, this would be my preferred method, but there is no bare shaft access. The pump is 4 wheels of about 8" diameter on a 20" shaft. It is directly mounted on the motor and does not have its own foundation. Its a weird product.

--------------------------------

It is my understanding that there are three main methods of extracting the modulation info:

1. It seems the overwhelming favorite and definitely the cheapest for a standalone device is the F/V convertors that measure time intervals for zero-passes. With this, the time interval between teeth 4 and 5 may be 480 samples, but between teeth 7 and 8 may be 517 samples, therefore torsional vibe. This is straightforward, but accuracy maxes out based on sample rate and there is tradeoff on precision of amplitude and precision of frequency depending on the encoder wheel resolution.

2. Alternatively, a more complicated/expensive frequency demodulation technique can be used to mathematically derive the modulation signal in post processing. These methods are way above my understanding and I won't even bother to try to understand, but once you have got a good working routine, it would automatic and very accurate in frequency and amplitude.

3. The final method is what I am trying to do, which is the sideband analysis. It benefits from higher precision with higher sample length and precision is not dependent on sampling rate. I am fairly certain this is possible to extract the torsional vibe frequencies and the amplitude for those discrete frequencies, but I am not sure how to formulate this extraction. This is an attractive option for me because we have a powerful, customizable (NI and LabView based with Matlab post processing) frequency analyzer that is capable of generating this information, I just need to know what I am doing so I can rationalize the results.
Curran919

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Reply with quote  #23 
Also, have you guys found Walt's missing message? It looks like it has gotten lost down here in the margin, haha.
John from PA

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Reply with quote  #24 
Quote:
Originally Posted by Curran919
Also, have you guys found Walt's missing message? It looks like it has gotten lost down here in the margin, haha.


As I had posted before, the message below is what Walt had earlier said.

Quote:
Originally Posted by Walt Strong

I hope that the OP (Curran99) will provide some feedback response to make this discussion worthwhile.

 

Walt

Curran919

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Reply with quote  #25 
Quote:
Originally Posted by John from PA


As I had posted before, the message below is what Walt had earlier said.

Walt



 Okay, so it only showed up for me like this then? [rofl]

2017-05-16 08_37_19-determining torsional vibe freqs from encoder sidebands_ - Vibration Analysis & .png 

Walt Strong

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Reply with quote  #26 
Curran,

Have you tried the NI torsional VI? Have you checked the NI resources? Here is a quick search:

Search: ni torsional vibration

 

Using the Torsional Vibration Measurement VIs (Sound and Vibration Measurement Suite)

 

Pasted from <http://zone.ni.com/reference/en-XX/help/372416A-01/svtconcepts/use_tv_vis/>

 

Performing a Torsional Vibration Measurement (Sound and Vibration Measurement Suite)

 

Pasted from <http://zone.ni.com/reference/en-XX/help/372416A-01/svtconcepts/perform_tv/>

 

measuring torsional vibration / frequency

 

Pasted from <https://forums.ni.com/t5/LabVIEW/measuring-torsional-vibration-frequency/td-p/1853333>

 

OAT Torsional Vibration (Digital Tacho) VI

 

Pasted from <http://zone.ni.com/reference/en-XX/help/372416B-01/lvoat/torsional_vib_dig/>

 

Torsional Vibration Analysis

 

Pasted from <http://forums.ni.com/t5/DIAdem/Torsional-Vibration-Analysis/td-p/3179648>


I have tried to write this with invisible ink, White Text, and vertical in the margin! What will happen next?

Walt
OLi

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Reply with quote  #27 
Upside down for those downunder? Inside out would be more complicated. Moebius ringed would be nice.
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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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Walt Strong

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Reply with quote  #28 
I thought about typing my previous response while riding on a merry-go-round. That would give me a rotational frame of reference and possibly some torsional vibrations as my grandchildren jumped around on their horses![rolleyes]

Walt
Barry

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Reply with quote  #29 
Things have gotten wired on this post guys. Where is Rusty when we need him.
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Barry
Walt Strong

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Reply with quote  #30 
Barry,

Do you have a contribution to our discussion about torsional vibrations, all kidding aside?

Walt
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