Dynamic Signal Acquisition

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shifting peak frequency

Hello,

 

I am measuring sound signals using a PCB microphone and NI9234 module. For identical conditions, the fft peak shifts by 2 to 10 Hz on both sides when I take multiple identical samples. Could anyone know the source of change please? The background noise is also similar throughout the measurement.

 

Many thanks for your reply and time

Jaefer

 

 

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Message 1 of 13
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Please provide more information about the signal source, connections, VI used to capture the signal, sampling rate and some sample data for review.

Santhosh
Soliton Technologies

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Message 2 of 13
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Thank you Santhosh;

 

Signal source: bubbling water in a tank

Matlab 2018a to acquire data

Sampling frequency 51200 Hz

sampling time 10 seconds

ICP® Electret Array Microphone model 130A23

NI 9234 

 

Data is so big to upload even for one sample.

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Message 3 of 13
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What phase noise ( jitter/ frequency shifts) do you expect from a bubbling water tank? 😄

Have a nice weekend 🙂

 

 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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Message 4 of 13
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Thank you, Henrik,

 

I don't expect any frequency shift.

 

Happy weekend to you too.

 

Jaefer

 

 

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Message 5 of 13
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Do you only care about low frequencies? If so, lower the sample rate by a factor of 10 or more and share multiple datasets. Give us some hints, what should I expect to see/hear from the spectrum of acoustic data from a bubbling tank?

Doug
NI Sound and Vibration
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Message 6 of 13
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Thank you, Doug.

 

I am interested in the peaks. If the parameters that bubble the tank do change during measurement, why does my peak frequency shift slightly? I just want to know the source of change.

 

My data file is more than 10MB, so I am not able to upload it here.

 

Jaefer

 

 

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Message 7 of 13
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One way to isolate if the shift in the frequency is in fact from the signal or an artefact of your code, connect the AI to a function generator that generates a clean sinewave, now your FFT should be consistent.

 

If the data file is larger, you can even do a smaller capture like 1 sec instead of the whole 10 sec. Do you think your issue will not be reproduced when using just a 1 sec capture?

 

BTW, you've not shared your MATLAB code so that any MATLAB experts could review whether you are doing things the right way.

Santhosh
Soliton Technologies

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Message 8 of 13
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Try Santhosh's suggestion (input a known signal to your system). You could also try somebody else's code ( https://www.ni.com/en-us/support/downloads/drivers/download.dsa-soft-front-panels.html#).

 

That's the best I can offer with no data and no code. 

Doug
NI Sound and Vibration
Message 9 of 13
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Many thanks, Santhosh:

 

I will apply your suggestion

 

I am using very generic code (attached in the file). I am afraid less than 10 seconds of data may not reproduce the scenario.

 

Here I have attached a file that contains the code, setup, and frequency domain graph.

 

Kind regards

Jaefer

 

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Message 10 of 13
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