FFT results are not reproducible

[AshaG]

I was trying to clean up my FFT power spectrum using the various averaging modes. I could clean it while the system was acquiring it through the DAQ assistant. While the data was being collected, I could work around wiith the various modes to clean up my FFT.

But when I use the waveform values from a stored data file and then try to use the same averaging mode, the FFT does not get cleaned. I could not figure out the reason.

Thanks,

Asha 

[GerdW]

Hi Asha,

do you mind to show any example vi, any example data, any expected results???

[AshaG]

Hi,

 I have uploaded two VIs - one for generating a waveform file and the other for reading it.I have put picture files showing my results for the RMS averaging mode. I have also added my data file.

Asha 

[altenbach]

When you read from file, you are only transforming a single trace, while during acquisition you are averaging 100 traces. To duplicate the result, you would need to read 100 traces in a loop (e.g. test_0.lvm ... test_99.lvm).

[AshaG]

HI,

 I am not able to follow you. I thought I had all the data I had collected in my file. Could you explain what you mean by test_0.lvm,test_1.lvm etc. I have written only to one file.

[Captain_Kirby]

HI AshaG,

Check the averaging perameters between the two VIs. In one, you are doing an RMS average, in the other, you do no averaging. In your RMS averaging, you are also only averaging 100 times. Given the current settings, there is no way the two measurements will be equivalent.