FFT

[mf_hussin]

Hi All,

I'm trying to develop the FFT program for voltage and current parameters for my monitoring application. The reason is to obtain the element for the THD such as 3rd harmonic from the FFT graph. My FFT graph show the data in continous form. How I'm going to change it to obtain in spike from. Hope to get some adivise from you guys..

[johnsold]

Is your data such that you expect to get a spike?

Many things can cause a spectrum to have broad peaks. Insufficient samples, peak location at spectral bin boundaries, noise, windowing effects come to mind immediately. Tell us more about you application. What is the sampling rate? What frequenicies are expected to be present in your signal? How many samples are you sending to the FFT?

Post your VI along with some typical data and someone will probably be able to help.

Lynn

[Kurt_NISalesEngineer]

Hi,

I'm wondering what version of LabVIEW you are working with. Have you had a chance to check out some of the awsome examples that are shipped with LabVIEW. Goto > help > find examples to launch NI Example finder. There are two vi's that I have found in LabVIEW version 8 titled:

1) Amplitude Spectrum (sim).vi

2) DC Centered Spectrum.vi

that might be of interest to you. I have also found a kool tutorial on FFT's check it out:

http://zone.ni.com/devzone/conceptd.nsf/webmain/03B5B1617959FCC286256AD200483C55

I hope this helps!

Kurt