Problem reading PXI 5122 with command AIReadAcquisition

[shawnyap]

Hi,

Here is some background information.

My sensor works between 0 to 800Hz and it gives an output (Please see attached file).

The 1st peak's period is stated.

I'm performing a Fast Fourier Transform (FFT) on it.

My question is, after FFT, am i expected to see an impluse at 700Hz(1/period)?

Thanks.

[Tica]

Hi Shawnyap,

A general answer to your question is yes. If you expect a single spike like what you show on your plot the FFT will give you an impulse at the inverse of the period. If on the other hand your signal is continuous (repeats itself over and over again) then the impulse will look cleaner or more defined but it will still be at the inverse of the spike period. I have modified one of our Example VI’s to show you what the FFT will look like. This is a really good way to look at the FFT of signals you simulate with LabVIEW.

Regards,

Tica T

Applications Engineer

National Instruments

[shawnyap]

Hi Tica Ti,

The waveform doesnt repeat itself, so I suppose i should only observe 1 spike at the inverse of period.

However, I do not have the Labview software to open the ext .vi file.

Is it possible for you to send me a sample using Labwindows?

Thanks.

[Tica]

Hi Shawnyap,

I do not have the code in LabWindows but I have taken pictures of both a sine and a signal similar to yours to give you an idea of what the FFT looks like.

Hope this helps,

Tica T

[shawnyap]

Hi Tica T,

I understand how will FFT will look like on my program. Thanks!

It's a pity that I cannot get hold of a Labwindow FFT sample program.

Is there anyone else who can send me a Labwindow FFT sample?

Thanks.

shawn