ilter <x@no.email> wrote in news:1146582612618-359556@exchange.ni.com:
> Dear All,
> I am acquiring analog signal and I am using 'filtering' , 'tone
> measurements' , 'fft' express vi's.I realized that fft found a peak
> frequency of a value which is 1000 times lower than the actual
> frequency. In my vi sampling rate is 1000 Hz, number of samples to be
> acquired is 1000. Looking at the
> attached example I figured out that I need the
> frequency spacing information. Using 'build cluster' I merged FFT
> output with sampling rate and resulting plot looked correct.But this
> does not solve my problem, since I need to have the dynamic data
> stream to be 'correct'. I need to find the frequency of a different
> signal using 'tone measurements' express vi which currently is giving
> a 1000 times lower value . I also want to use filtering vi, which does
> work properly under this condition. Any suggestion will be more than
> appreciated. Regards,
> ilter
>
>
> fft.JPG:
> http://forums.ni.com/attachments/ni/170/182552/1/fft.JPG
>
Since you sample rate is 1K, and you're getting a max at a frequency 1000X
less than you would think, you must be getting a max at .3Hz or less, I
would imagine.
Subtract the mean from your signal before taking the fft. Better yet, fit
the whole data set to a line, and then subtract out that line, and take the
fft.
--
Scott
Reverse name to reply
Using the Abort button to stop your VI is like using a tree to stop your car. It works, but there may be consequences.
