Check for Sinusoid

[ATE-EGNE]

Background: Widget Co. Is building a new line of devices that, if wired correctly, output two sinusoidal signals(S1,S2) based on a knob position (Θ) and constant sinusoidal signal (I = 5V at 400 Hz) If a device is correctly wired, the following table should be true

Θ    I, S1 and S2

0     I = S1 = S2

45   I = 2*S1 = -2*S2
90   I = -S1 = -S2

Problem:

If I'm using the NI-DAQmx Express VI to acquire data from the device as a tester rotates the knob smoothly from Θ=0 to Θ=90. What is the best way to analyze the collected signal data to make sure that the device is wired correctly?

keeping in mind that a human operator will be doing the turning so Θ will be turned from 0-ish to 90-ish and smoothness of "smoothly" will vary.

Right now, I'm just taking one sample wavefom at 0, 45, and 90 based on when the user clicks a "test at point" button, but I'd like to know if there would be any way to get LabVIEW to directly track the change in S1 and S2 over time relative to I

[RavensFan]

I would do an FFT on the signal.  The two highest peaks would represent the two sine waves that make up the signal.

If you do this on a windows of the signal that you move along in time, you should be able to track how the frequencies of the sine waves change in time.

[ATE-EGNE]

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@RavensFan wrote:

If you do this on a windows of the signal that you move along in time, you should be able to track how the frequencies of the sine waves change in time.

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I'm not sure what you mean by widows of the signal: could you provide a link to the appropriate VI's or an example?

[RavensFan]

Let's say you have 10 seconds worth of a waveform,  do the FFT on 1 second of the waveform, then the 2nd second, then the 3rd second.  .....  Now you'll have 10 FFT's that represent how the sine waves changed from second to second.  That second Is the "window" of the original waveform collected.