Multifunction DAQ

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Frequency Analysis

Hi, I'm using a piezoelectric stack  to generate some ultrasound in water to caluclating maximum pressure inside the beaker i'm using, for that i'm using labview Spectrum analysis(FFT) to find the resonance peak. first i'm sending uniform white noise to check where the maximum harmonic  i got  then at  that frequency i'm sending sinewave to get the resonace peak. that what i'm trying to do, but when i send white noise and , sine there is no difference in the FFT spectrum is anything wrong in my vi?

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Message 1 of 29

I do not have the Sound and VIbration toolkit so I cannot see some of the subVIs.


My first question is how confident are you that a strong resonance actually exists? A beaker of water may have significant damping and the low spectral density of a white noise signal may not excite that resonance well. Are you looking for the resonance of the water/beaker system or of somethng else? Do you have a good model which predicts accurately where the resonance should be? How broad do you expect the resonance to be?


Some of the default settings on your VI are inconsistent with your description. Sine wave signal rather than noise for example. And the sample rates being different on the DAQmx VIs and the SV Signal Generation VI.


I cleaned up the diagram on your VI. With crooked wires, wires behind other objects, right to left wires, and other issues, it is very difficult to determine what the VI is supposed to do.




Cleaned up loop.png

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Message 2 of 29

Hi john, we developed  the beaker model in comsol multiphysics, we find the good and maximum  pressure at the center and bottom of the beaker and later we send it to laboratory and made according to comsol dimensions. I had attached the image that was the older one when we use stinger and now we are using piezo stack. In that we placed pressure at bottom of the beaker.we used CLIO software and interface there we find maximum of 190dBSPL. now we are using labview to controlling of frequency and power.....

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Message 3 of 29

Can you post some data which you have received from the piezo stack? The time domain data before the spectral analysis.



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Message 4 of 29

Hi John, At present i doesn't have access for labview, so by tomorrow morning i will send you the time domain data is it ok?


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Message 5 of 29

Whenever is convenient for you.



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Message 6 of 29

Hai i had attached the time domain spectrum images before doing FFT analysis..

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Message 7 of 29

I would like something with the actual data so I can work with it. Either a VI with the values saved as default or the data saved to a file.





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Message 8 of 29

Hi John i had attached my vi with default this ok ?

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Message 9 of 29

That has defalut setting for the controls but no data. Actually your VI does not have an indicatro where I would like the data. Right click on the data output of the DAQmx Read inside the loop and select Create Indicator.


Data collector.png


Run the VI until some tyipcal data is in that indicator. Stop the VI. Right click on the new data indicator and select Make Current Value Default.


data indicatpr.png


Save the VI (probably with a different name) and post that.


Then the VI will have one iteration of raw data from the DAQmx Read so that I can see what is going on.



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Message 10 of 29