High sampling rate with harmonic distortion anlyzer

[obarriel]

I have an adquisition board capable of working up to 25MS/s, normally I work bettwen 05MS/s-10MS/s. The adquisition itself works ok for any sampling rate I choose. The problems starts when I use harmonic distortion analyzer with the adquisition. If I choose slow sampling rates everything goes ok, and (at a fixed FFT size) the harmonic distortion analyzer give me the result at a increasing speed as I increase the sampling rate (as logical).

But there's a point when I reach a kind of limit, and when I increase the sampling rate, the speed does not increase. For example using a 1MS/s I have the same speed than when using 10MS/s if I am using the harmonic distortion analyzer in situ with the adquisition.

Hope there is any solution

Thanks!

[obarriel]

I suppose that the answer is that FFT is a CPU time demanding activity when using big FFT sizes, so increasing the sampling rate won't increase the speed since the speed limit is fixed by the FFT.

Is there any way to improve harmonic distortion analyzer speed?

[AitziberH]

Hi,

do you use the harmonic distorsion analyzer inside the acquisition loop?

Doing any kind of processing inside an acquisition loop can be a problem if you are managing lots of data at high speeds, cause each iteration slows down while the PC buffer keeps filling up with the data coming from the board, and the loop is not as fast as this if it have to do a slow process inside each iteration.

Even it could show you a message error indicating that the pc buffer has been overwritten.

This could be solved making the pc buffer bigger with the DAQmx Input Buffer.vi instead of letting the task decide which size to apply, or maybe doing the analysis calculations offline.