Using Extract Single Tone Information to detect phase

[looloo]

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

[tbd]

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!

[looloo]

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

[tbd]

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!

[ssingh1]

Did a little modification to looloo's code to correct phase change(by having fixed time input).  🙂