From Friday, April 19th (11:00 PM CDT) through Saturday, April 20th (2:00 PM CDT), 2024, ni.com will undergo system upgrades that may result in temporary service interruption.
We appreciate your patience as we improve our online experience.
From Friday, April 19th (11:00 PM CDT) through Saturday, April 20th (2:00 PM CDT), 2024, ni.com will undergo system upgrades that may result in temporary service interruption.
We appreciate your patience as we improve our online experience.
11-09-2007 10:15 AM
11-09-2007 10:21 AM
1) What is the phase output of the Spectral Measurements Express vi? I've seen several examples using this function and none of them use the phase output. If I put in a simulated sine wave with no phase offset, the FFT phase output is -90 deg at the input freq.
11-09-2007 01:30 PM
11-12-2007 03:34 PM
FFT-based spectral computations assume that the finite block of signal data represents one period of a periodic signal. The computed spectrum of this effective periodically extended signal shows energy spreading into frequencies that were not present in the original signal. To reduce this spectral leakage, use smoothing windows to taper the sharp transitions in the effective signal. You do not typically use windows if you can acquire an integer number of cycles of each frequency component measured or if you are analyzing noise spectra.
In response to question 2, the amplitude of the Tone Measurements Express VI returns the amplitude of the detected single tone in Volts peak (Vp).
In response to question 3, what is the phase of the signal that you're measuring? I used this VI with a Simulate Signal VI and simulated a sine wave and was able to correctly use the Extract Tone VI for all phases. Have you tried doing this?11-13-2007 07:21 AM
Hello Amanda,
Thanks so much for your helpful answer. This ("FFT-based spectral computations assume that the finite block of signal data represents one period of a periodic signal.") was particularly useful, since it doesn't appear in my help window. I'm using 7.1 and it looks like most of the the answers to my questions are in the version 8 help.
I tried to follow the link at the bottom of your reply and it didn't go anywhere, but knowing that the information was out there, I searched through the NI website and found what I think you were referring to. Is this it?
http://www.ni.com/pdf/manuals/370355f.pdf
It talks about Zoom FFT. Do your reply and the information in the pdf pertain to the 7.1 Spectral Measurements Express vi as well as the version 8 Zoom FFT?
Regards my question 3: I'll double check tomorrow when I return to my office (I'm in a lab in another town today).
Many thanks for your help. I can see why no one answered me - they know the information is in the help. But, I can't see the same help they are, because I'm using a different version of LabView.
Margaret
11-14-2007 08:26 AM