Showing results for 
Search instead for 
Did you mean: 

FFT of recorded waveforms

Go to solution

Hi all,

        I am pretty new to LabView and data aquisition. Sorry to bother you all. I have a question:


"I have recorded a distorted waveform using digital oscilloscope. The format of the file is .bmp i.e. Paintbrush picture. I want to perform the FFT analysis of this waveform. How can I do it in Labview????? I already have the magnitude spectrum using the FFT mode of the oscilloscope, but I need to get the phase spectrum as well so that I get the phase angle for each of the harmonics. Could you be very kind to guide me in this regards????"


         Thanking in anticipation.


Best regards,

0 Kudos
Message 1 of 31
You will have to record the waveform in some other data type. I don't think it's possible to do anything at all with an image of it.
Message 2 of 31
yeah I suppose you could analyze the .bmp image to try to estimate numbers but it'd take waay more time than it's worth and probably wouldn't be that accurate.  See if you can get your oscilloscope to give you actual numbers.
Message 3 of 31

Thank you very much for the reply. What other formats would you suggest me???


The only resources that I have to get the waveforms are Tektronix Oscilloscope, Current Probes, Labview, USB-6259 DAQ device and a computer. I want to record and analyze the waveforms for various electrical appliances e.g. iron, computers etc. I think USB-6259 cannot be used with such kind loads which may draw current around 10-12 amps at full load.


your guidance in this regard will be very helpful for me.



0 Kudos
Message 4 of 31
Connect the scope to the pc with RS-232/USB/Ethernet and transfer the waveform data to the scope. That's assuming that this scope has some sort of remote control capability. If it does, LabVIEW is perfect for that and chances are, you will find some prewritten code. Otherwise, read the manual and see if you can save the data as xls, csv, etc. How did you get the bmp from the scope to the pc?
Message 5 of 31

Thank you very much for your reply. I tried to connect it using Ethernet but unable to do it. I don't know how to do it using Labview. Do I need a cross cable or straight cable for ethernet???

I got the .bmp file using the capability of the oscilloscope.


Anyways, the good part is that, I have finally got some data information in .csv format. It's not very precise and I am still working on to get a more reliable data.


So, considering the fact that i have now got the data in .csv format,what should I do next to perform the FFT analysis in Labview??


Thanking in anticipation

0 Kudos
Message 6 of 31

Most oscilloscopes generate 8-bit data.  So you will never get "very precise" data from a scope.  Eight bits is equivalent to between 3 and 4 significant figures in decimal representation.


The simplest thing to try with your .csv data is to read it with the  Read from Spreadsheet, recalling to set the delimiter to match what is in your file if needed.  If that gets you an array with the data in the right format, just feed it to the FFT function.



Message 7 of 31
And hopfully, the csv file includes some timing information. Without it, you will have to manually provide it to the FFT function.
Message 8 of 31

Thanks for the reply again. I have read the data from .csv file in Labview now. But there is a confusion, there is a third column in output as shown in the attached scnreenshot. The two side ones are read from the two columns available in .csv file but the middle one which has only zero values is there for no reason known to me.


Now, how can I generate a waveform from this available data in the Labview?? May I please also know, what do you mean by time information.


Your reply will be of great help to me.


Thanking in anticipation.


Best regards,


0 Kudos
Message 9 of 31

It's unknown to me as well since you did not attach the csv file. Unknown to me is how you actually saved the file and what options for doing this are on the scope.


If you wish to extract information in the frequency domain, you need to know the sample rate of the signal.

0 Kudos
Message 10 of 31