Extract Single Tone Information - phase step

[Thomas_S]

Hello!

I am using Extract Single Tone Information to measure amplitude, frequency and phase of a slowly varying signal.

But sometimes the phase jumps ~350 degrees for no apparent reason. I have made a small vi (in LabView 8.5 professional) to demonstrate this, see attachment.

Seems like the shift occurs when the ends of the input signal cross each others level, in opposite directions.

Guess I should start looking for an alternative method for doing the measurements.

Any suggestions or ideas are most welcome.

[Øyvind Ø]

Hi Thomas

It jumps 360 degrees to be exact. -180 degrees and +180 degrees is basically the same thing so the phase you are seeing is correct. It does not look very good in a chart though. To improve the looks you can use the subVI called "Unwrap phase".

Regards

Øyvind Ø 

[Thomas_S]

Yes, I have figured it out.

I just didn't use the unwrap_phase vi correctly.

Anyways, thanks for the input!