Increasing FFT resolution using zero padding using niScopeFetchArrayMeasurement

[salomiva]

Hello!

I am using NI PXI-5124 digitizer to fetch data from a piezoelectric sensor. I need to analyze the spectrum of the signal in real time so I am using niScope Fetch Array Measurement Cluster.vi to calculate FFT.

In the Help it is explained how FFT works: “The FFT amplitude spectrum is calculated using a split-radix real FFT, and the frequency corresponding to the maximum amplitude is returned. If the input waveform size is not a power of two, the waveform is zero padded to the next higher power of two. The frequency resolution is

sampling rate / number of points”.

Is it possible to increase FFT resolution using additional zero padding, i.e. to pad more zeros than the algorithm does by the default? For example, for the signal length of 4000 to pad 4192 zeros and to get the FFT lenght of 8192.

[DFGray]

No, but you can do the same thing, with little, if any, time penalty, by fetching the data from the scope, padding it yourself, then using Extract Single Tone Information.vi to get the dominant frequency.  You may not need to pad your data, since Extract Single Tone Information.vi does the equivalent of a curve fit on the top points of the frequency peak to give you sub-sample accuracy.

You will need either a student of full version of LabVIEW to use this VI.  It is not included in the base version.