Take measurements from analog input and put it on a text file

[rockgoldem]

Hi

I am new to Labview and I really have no idea. I am using DAQ PCI-6251 and labview 2011.

The analog input will receive a swept frequency signal (500hz - 20000 khz) with a 500 hz step.
I want to take the measurements and save it on a text file.
The measurements on the text file should be " all the detected frequencies and the corresponding peak to peak amplitude "Voltage", dB power.

Please help, I need this to get my project done. Could someone post the required VI file please.

I tried to find it on the "Find Examples" but I could not

[Hooovahh]

Well it sounds like you tried a few things so that's awesome for you.  One issue, you said you need to measure a frequency ranging from 500Hz to 20000khz (or 20MHz).  You will have a hard time finding DAQ hardware that can characterize a signal like that because nyquist says you must sample 10 times as fast (real world nyquist) so you need hardware capabile of sampling at 200MHz.  I hope this was a typo and you actually have an input from 500Hz to 20KHz then you need to sample at 200KHz which is much more doable.

Another issue is you never mentioned was how quickly the frequency changes to the next step.  While the sampling is hardware timed, if you don't have multiple cycles at each frequency, you are going to have a real hard tim detecting the different step changes.

If the two issues above are addressed then the easiest way is to use the DAQ Assistant.  Configure it to read the channel you have on your system, at 200000.  You need enough samples so that the slowest wave can be characterized.  Meaning probably 10 cycles at 500Hz which is 20ms.  20ms at 200KHz is 4000 samples.  So that means you need to take 4000 samples at 200KHz and measure the peak, db Power, and frequency then log those to a file using the Write to Spreadsheet file under File I/O.  Look under the Signal Processing >> Waveform Measurement to see what options you have for measuring the wave that the DAQ Assistant returns.