measure out of phase signal

[simimasa]

I want to measure a signal with in phase and out of phase part, how can I set up a VI to measure them separately?

[simimasa]

I want to add something more so that you can fully understand what I'm talking about.

The signal I want to meaure consisting two parts, with phase of 90 degree apart. What I want to do is to extract these two mixing signals out and display them in a waveform chart.

Thanks in advance!

[dnchen]

Wouldn't two signals that are out of phase just appear as one signal?

See cos(x)+sin(x): http://www.wolframalpha.com/input/?i=cos%28x%29%2Bsin%28x%29

If that's the case, you can mathematically calculate what the two signals are from the characteristics of your signal, and then recreate the two separate signals

[simimasa]

Hi, thank you for your reply.

The signal is in the form of a+bi, it's a complex number, and I want show a and b separately. Do you have any idea of how to achieve this?

Thanks again!

[Henrik_Volkers · Accepted solution]

The phase of a signal related to what?

For a phase measurement you always need a time reference (or a reference phase of another signal)

If you have a coarse sine signal you can try the tone detection vi , the output is amplitude and phase, so you just have to calculate a and b (see the complex number functions)

Or you use the FFT vi and get the already complex bins at frequencies that hopefully match the ones you are looking for, unless you match the input data (or do some more math 😉 , BTW that's what the tone detection vi does)

[simimasa]

Hi Henrik,

Thank you for your kind reply.

As for the measured phase related what, I will set one of them as reference, the other will be 90 degree apart. The point is that I want to extract a and b from the signal, as they both represent valuable parameters, by doing this I can get two equations to solve for the unkowns. By the way, this method is called 3 omega method to measure the thermal conductivity in thin film.

I will try these two vi and will let you know whether it works or not.

Thanks!

[simimasa]

Hi, I think the FFT spectrum (Real-Im) VI may work for me. But I don't know how to display the output signal in a waveform chart, as it's a 3 elements cluster. Why it is a 3 elments cluster? Could you please tell me how can I disppaly and store them?

Thanks!

 

[dnchen]

Use the "Unbundle by Name" function on the cluster and select real/imaginary part. This is basic clusters! http://www.ni.com/white-paper/7571/en/

[simimasa]

Hi,  thank you so much. I have worked it out.