04-25-2009 02:49 AM
Dear all,
I have problem using Extract Single Tone Information vi to detect phase angle of a sine wave.
I posted similar question a few days ago regarding using the same vi to determine phase angle of a square wave and realised it couldn't be done because square wave is not single tone. I modified my program slightly and use it to examine a sine wave but I still couldn't get reliable results.
Please find the attached for the program code. When I set frequency to 5 Hz, everything worked fine but when I set it to 5.17 Hz with 20 degree phase, the detected phase value keeps changing. Appreciate if you could help me on this matter. Thank you very much!
Best regards
04-25-2009 03:36 AM
Hi looloo,
I've added a second chart to your VI to make it obvious what's happening. The second chart shows the Y-array input to the "extract single tone function". Phase - or starting-angle - changes periodically, when array-index output from Modulus-function "wraps" back to zero.
Cheers!
04-25-2009 03:56 AM
Hi tbd
Unfortunately I couldn't open your file as I am using LabVIEW 8.2. Do you mean that the sample size chosen is not appropriate?
Thanks
Best regards
04-25-2009 11:40 PM
Hi looloo,
Sorry for slow response! Here's the VI back-saved to LV8.2
(in case It's not too late to help...)
The "phase" output reflects the "angle" associated with the beginning value in the Y-array (when Y = amplitude, Phase is 90deg.)
Phase is changing because sine-wave (Y-input) is shifting each time single-tone is called...
Cheers!
04-26-2009 01:13 AM