phase of a signal

[Hillman]

Hi,

The Extract Single Tone Information.vi you find that the data is apparently derived from a complex FFT. I think the phase you get from an FFT is related to the reference function. I quote from Chapter 4 of the LV Analysis Manual:

"The phase is relative to the start of the time record or relative to a single-cycle cosine wave starting at the beginning of the time record. Single-channel phase measurements are stable only if the input signal is triggered. Dual-channel phase measurements compute phase differences between channels so if the channels are sampled simultaneously, triggering usually is not necessary. The phase is the arctangent of the ratio of the imaginary and real parts and is usually between π and –π radians, or 180 and –180 degrees."

Amp and Phase spectrum seems to be the cause of it. Its always important to pass the expected data form to these functions. And I imagine we're not passing or understanding the output of the amp and phase spectrum properly. However, from the help, I couldn't work it out.

Any ideas?

Kind Regards,  

[IanW]

The LV Analysis Manual sounds like a useful document. I tried searching for it on the NI site but couldn’t track it down, any ideas where it's hiding?

 Thanks. Ian

[rpursley8]

All that is true, but why does the vi within Extract Single Tone Information called Extract Single Tone Information from Hann Spectrum literally adds 90 degrees to the phase output as a last step before the output (nested sequence structures (ugh!!!))?  That is the only part I don't understand.

[ssingh1]

It seems that it has something to do with the single-cycle cosine wave referance used by FFT Function (sine and cosine are 90 deg. out of phase)

Message Edited by ssingh1 on 11-11-2009 03:55 PM

[mahammed1116]

hi,

  I need to see extract single tone information.vi block diagram.could u send the vi.actually it is locked in my labview.please sned it ASAP.i need to know how they are calculating the amplitude and phase from time domain signal.it is required urgently for me

regards

mohammed