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FFT Spectrum (Mag-Phase) VI output vs SCOPE display (Delta Y seems different)
yeah
07-30-2022 11:46 PM
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Hello All,
I try to do FFT analysis for attached time-volt waveform, but the result seems different between FFT Spectrum (Mag-Phase) VI and the scope itself. Does anyone could give me some advice for the cause of the differece?
as you can see, the Delta dB is about 66 on the scope screen while it seems should over 75 in labview.
santo_13
07-31-2022 12:06 AM
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You're just giving two bottles of juices and asking why they are different without giving any information about whether the same fruit, the same juicer was used etc.,
Similarly, did you give the same exact signal to both? how do the instrument specifications compare?
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07-31-2022 01:33 AM
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Hello Santhosh,
The input was the same square wave. The top picture of the second attachment is read out from the scope by USB connection.
santo_13
07-31-2022 09:26 AM - edited 07-31-2022 09:31 AM
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What instrument did you use to get signal capture into LabVIEW?
Edit: In the FFT VI I would recommend using rectangular window and removing averaging, windowing improves the noise floor and you'll get better results. Do you know the settings on your scope for FFT?
Soliton Technologies
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07-31-2022 04:23 PM
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Hello Santhosh,
The instrument is Tektronix scope 1102x.
there is not too much setting we could do for this model. Tried the settings seems do not have too much impact on the result. I tried rectangular window and removed averaging, it seems almost the same.
But I was thinking wether the scope have a filter in its FFT calculation to remove something. I'm really new in FFT analysis and still not very clear about FFT. I will continue to have try.
Thank you too much for your inputs.
