How to measure relative phase of several sine wave inputs

[Scott56789]

I'm using a USB-6229 to acquire 10 sine waves, and I would like to output their rms amplitudes and relative phases.  The rms amplitude is not a problem, but I wasn't sure how to go about determining the phase of one signal relative to another.  Do I need to use the Frequency Response analysis step?  Thanks.

[hoffiz]

Hi,

There are some functions you can use to measure the relative phase. You can either measure the phase of every signal related to another one using like you said: a frequency response function step. Using one of these to functions might do the job: “Frequency Response, Express VI” or “Frequency Response Function (Mag-Phase).vi, if you are working in LabVIEW. The first one of these functions "Frequency Response" is also found in signal express and is the one I think you are refering to.

Although this functions is use for a stimulus response approach they will give you the relative phase of Y with respect to X, “Typically, time signal X is the stimulus, and time signal Y is the response of the system.  in signal express your options is the frequency response step.

I would also like to point you to some references that might serve you as reference when doing spectrum analysis: An Overview of Frequency-Domain Measurements and FFT Analysis.

Message Edited by Jaime F on 02-06-2008 11:42 AM

[Scott56789]

Hi, thanks for the fast response.  I'm measuring power system signals (60Hz sine waves), so I was hoping to have the "frequency response step" output the phase at 60Hz only, not the entire spectrum.  Is this possible only using SignalExpress or do I need a LabView vi?  I don't have LabView, can I still use a VI to accomplish this if a VI is needed?

thanks,

-Scott

[hoffiz]

Hi,

You have to options: one is to zoom into the frequency response graph step in Signal Express by changing the limits on the x-axis and approximate the phase at the desired frequency or get LabVIEW where you can manipulate the data retrieved form the function to show only the phase at the desire frequency.

I hope it helps