Phase Response

[viksen]

Hi, I've set up a program which inputs a sinusoid to hardware via labview and a daq, and retrieve its frequency response via a position sensor to the DAQ. I can receive the amplitude of response, however, I'm not sure how to find the phase of it (so i can see the phase lag between input and output).

I would appreciate it if someone could help me with this.

Much thanks

Viksen

[YatinM]

Hi

Could you describe your setup a bit more. Which version of LabVIEW and drivers are you using? From the top of my head I think you might be able to use Extract Single Tone Information.vi, this allows a signal to be input and it gives the information on amplitude, frequency and phase of the signal. The function can be found at Signal Processing >> Waveform Measurement.

Let me know more information and I will be able to help you more

Kindest Regards

YatinM

Message Edited by YatinM on 05-25-2007 04:13 AM

Message Edited by YatinM on 05-25-2007 04:15 AM

[johnsold]

Viksen,

From trigonometry the product of two sine waves of the same frequency has a zero frequency component proportional to the cosine of the phase angle difference and a second harmonic component. Multiply the input and output together. Filter the product (or use AC/DC Estimator) to get DC component. Scale appropriately. Result is cosine of phase shift.

Lynn

[Matt_W1]

You could use cross power spectrum  on the two signals, find the index of maxium magnitude (array min & max) use that index to find the right phase (index array). You can multiply the the index by df to get the frequency it detected.