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Noknroll

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At what frequency would you expect to hear a ringing noise (sorry Dan Timberlake I believe describing noises are your pet hate) I was asked to look at a Francis Turbine that was making a ringing/squealing noise at 80 - 100% guide vane opening.
I only have data out to 5000Hz. Operating speed is 428rpm/7.13Hz
When guide vanes approach and exceed 80% opening there is a clear increase in amplitude at approx 1600Hz and virtually nothing from there up to the 5000 Fmax. 

So, is 1600Hz in the human audible range? and would it be considered high pitched?


Edwin

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The 1600Hz could be the noise you hear. Typical frequency of a dry bearing is around 3500 Hz. More severe damage occurs around 1500 to 2000 Hz. But that sounds more like growling.

Do you know if there are oil slinger rings there? They can also generate a ringing noise but it will not be seen in vibration. The energy in it is too small. But it will show as copper particles in the oil.

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John from PA

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1600 Hz is certainly in the range of human hearing.  You might try an online signal generator to generate a 1600 Hz audible tone and see if it is close to what you actually hear.  The one I use is at http://arachnoid.com/SigGen/index.html.  By default it generates a 440 Hz tone which is adjustable in the Signal Generator Properties section.  Once the frequency is adjusted, uncheck the "Mute output audio" (see below).  The audio is muted when you first go to the website.

sig_gen.jpg 

jvoitl

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Slightly over 1661Hz is the 72nd out of 88 keys on a piano.
Batman

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Recently I was helping my son with some physics, (on waves) and his textbook claimed that audible sound to the human ear is from 20Hz to 20kHz. I'm sure mine is not that good[redface]
Danny Harvey

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Reply with quote  #6 
They probably got that reference off of some loudspeakers.

Some may be able to hear that range but most can't.

We discussed this recently and John contributed some very good information about how amplitude enters into the scenario.

You might look back and find it.
Noknroll

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Thanks All

Edwin, the high pitch noise is coming from the volute housing, bearings are hardly affected and not showing the higher amplitude.

John from pa, thanks for that link, 1600Hz in that signal generator could well be what I was hearing. I guess there has to be some difference in lap top amplifier and speaker quality 

jvoitl, that 72nd key is getting up there in the higher pitch region.

now I'm off to find the discussion you refer to Danny.
John from PA

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Quote:
Originally Posted by Noknroll
Thanks All
now I'm off to find the discussion you refer to Danny.


This thread, http://www.machineryanalysis.org/post/gear-train-problem-8197308?pid=1293788992 and item #47.
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