sampling frequency

[maleeho@hotmail.com]

Hi

We are using  Tektronix scope TDS3012B, function generator GFG-8250A, and NI488.2 GPIB to interface the scope to PC.

FFT analysis is carried  successively for sinusoidal signals of different frequencies and amplitudes using FFT VIs.  ( we are using LabViEW 8.0in ower Lab).

My question is that what would be the sampling frequency for the system we are using, since for any   frequency we are adjusting for the sinewave we got exactly its value in the frequency spectrum. Does it has any relation with the scope sampling rate and frequnecy.

Thanks alot and regrads 

maleeh

[S_Hong]

Hi maleeh,

In order for any FFT to return the correct frequency components of your signal, you must ensure that your scope samples at a rate which does not violate Nyquist Theorem which states that your sampling rate must be larger than 2 times the largest frequency component you wish to detect in your signal. However, a general rule is to sample at 10 times the largest frequency in order to have a nice time-domain representation of the signal. I believe that most scopes will automatically set the proper sampling rate for you as long as your signal is within the scope’s specifications.

Nyquist Theorem
http://zone.ni.com/reference/en-XX/help/370592G-01/digitizers/nyquist_theorem/

I hope this helps,
S_Hong

[maleeho@hotmail.com]

Hi,    S_ Hong

Thanks a lot for your information regarding the sampling frequency.

Regards

maleeh