How to get the phase difference between two channels

[weatherhound]

I have two incoming channels via a 4472 DSA card. I want to compare the phase response of the channels and graph the difference between the phases of both channels. I'm using labview 7.0. any hints? thankyou, Jim

[dsb@NI]

Do you have the LabVIEW Sound and Vibration Toolset 3.0? If so, perform an acquisition and use the SVT Gain and Phase VI to measure the interchannel phase mismatch.

Using analysis available in the Full and Pro versions of LV you can perform a similar measurement using Extract Single Tone Information.vi found in the Analyze-->Waveform Measurements palette. Subtract the phase returned by each instance. The phase of either channel independently is irrelevant, but the relative phase should be accurate.

[Ahmed Khwaja]

are u sure name of the vi is SVT Gain and Phase VI. Because I cannot find such vi. There are other subsets or vi like SVT FFT, SVT frequency etc. Can you be more precise.

Thanks

[dsb@NI]

Yes, the name of the VI is "SVT Gain and Phase.vi" If you have the Sound and Vibration Toolset 3.0, this VI is in the Sound & Vibration-->Single Tone Measurements palette.

This measurement was not available in the Sound and Vibration Toolset prior to version 3.0.

[AVR]

If you want the phase information, perform an FFT and keep the imaginary portion of the result. Most users perform an FFT to get a single-sided, real-valued output. This buries the phase information in the amplitude of the real output due to the fact that the single-sided operation multiplies the results of the FFT by its own complex conjugate. As the imaginary data represents the phase information (muliplied by "i"), you can use the complex portion of the FFT result for your comparision.

[Jamaloogy]

Hi dsb@NI...

Regarding your quote...

Do you have the LabVIEW Sound and Vibration Toolset 3.0? If so, perform an acquisition and use the SVT Gain and Phase VI to measure the interchannel phase mismatch.

Using analysis available in the Full and Pro versions of LV you can perform a similar measurement using Extract Single Tone Information.vi found in the Analyze-->Waveform Measurements palette. Subtract the phase returned by each instance. The phase of either channel independently is irrelevant, but the relative phase should be accurate.

Doug B
National Instruments

I have one important question..

I have NI digitizer that has two channel that use to measure 2 voltage.. from it I want to find the phase difference by comparing channel 1 and channel 2... can I use your stated method above? Now I'm unable to test it because I don't have the function generator due to RMA..

thank you

[dsb@NI]

I am attaching two example VIs. The first example illustrates relative phase measurement when a tone (energy at single frequency) is input to the two channels of interest. The second example illustrates how you can use the frequency response function to measure the broadband (energy at all frequencies) phase response between two channels.