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'How to measure frequency(noise) of boiling fluid?'
1998\11\20@184943 by PHXSYS

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Hi

I was wondering if anyone could recommend a method for measuring and
determining the noise frequency of a boiling fluid. I want to use a mic to
determine the boiling point of a fluid. The temperature range for boiling
point of my fluid is 200-500 deg F. I am looking for a simple method to
determine when a fluid is boiling.

What kind of frequency analyzer would I need?

Thanks

Jon

1998\11\20@185356 by Harrison Cooper

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I was just talking to a friend on 2meters the other night (K7ZTM), and he
was talking about a spectrum analysis program that you could read in a .wav
file and analyze the entire file.  But it might not be shareware, not sure
about it.

{Quote hidden}

1998\11\20@191050 by Scott Dattalo

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On Fri, 20 Nov 1998 .....PHXSYSKILLspamspam.....AOL.COM wrote:

> I was wondering if anyone could recommend a method for measuring and
> determining the noise frequency of a boiling fluid. I want to use a mic to
> determine the boiling point of a fluid. The temperature range for boiling
> point of my fluid is 200-500 deg F. I am looking for a simple method to
> determine when a fluid is boiling.
>
> What kind of frequency analyzer would I need?

Hi Jon,

This sounds very similar to Andy's desire to 'listen' to the sound from
his boat's prop to ascertain its RPM. Check the DTMF thread from a couple
of days ago (or wait a couple of weeks for it to automagically re-appear)
to see a method Payson and I discussed. But to summarize, you'd probably
want to implement something like this:

1) Hardware low pass the signal (I presume the frequency is relatively
low).

2) Sample about 4x the filter's cutoff point.

3) Compute the energy of the signal

4) Perform a frequency decomposition of the signal (e.g. fft)

5) Normalize the fft by dividing the binned frequencies by the total
energy. This division doesn't have to be a 'real' division. Instead, it
can define the threshold used to determine whether or not a frequency bin
contains 'a strong component'.



OTOH, I presume that the boiling rate changes slowly and hence the
frequency is relatively constant (that is, while the measurement is being
performed). That being the case, it may make more sense to just cycle
through several bandpass filters. This is more like the '2nd solution'
posted in the DTMF decoding thread. I suspect you can use the 1-bit A/D
converter decoding technique quite reliably to implement this.

Scott

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