Determine phase shift ben input & output

hello guys,
I want to determine the phase shift between input and output signals. I want to measure the phase difference as lomg as I apply input. And save that to a file for reveiwing it later.Can anyone please help me with that. I am using Labview 7.1.
Thanks,
Jinal

Hi Jinio,
Please take a look at the following KnowledgeBase article:
How Can I Determine Phase Mismatch Between Two Channels?

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Unfortunately, I wouldn't consider this very likely at all. While there is 8 DIO lines on this boards, you only have immediate software update control over them. (No strobed, hardware-timed output.) So you'd need a program that constantly toggled the state of these lines which would not be very fast or deterministic for that matter.
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In LabVIEW 6.0, I am attempting to apply a uniform phase shift to a non-periodic waveform but have run into a problem. Theoretically, if I take the Fourier transform of the signal, apply an offset to the phase and then take the inverse transform of that, the output of this process should be my original waveform with all of its frequency components delayed by the same number of radians (different amounts of time). However, I am not getting this result from LabVIEW. In the attached example code I generate a sine wave burst, take the FFT, convert from cartesian to polar, apply an offset to the phase, convert back to cartesian and take the inverse FFT. However, instead of getting a phase-shifted, same-amplitude versio
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Attachments:
phase-shift.vi ‏51 KB

This only works (partially) if your array size is an integral power of 2 (e.g. 512, 1024, etc.), i.e. in cases where the fast fourier transform can be used.
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Please see my example posted HERE
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I am using LabView7.1 and am trying to understand how the FFT measures the phase difference between 2 analog input signals. The 2 signals have about the same amplitude and their phases will be about the same. I am getting a phase difference of exactly 0.000000 but there should still be a difference. Not sure how the FFT block compares the two signals. Do I need to specify which is the reference signal? If so, how do I go about doing that?
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BTB Acceleromter.vi ‏378 KB

I admit this is not 100% on mark but may give you some ideas. In this thread I suggested using a zero-phase shift filter. Ignore this post if it does not help.
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Ben Rayner
I am currently active on.. MainStream Preppers
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Hi,
I've recently started a project where the idea is that we have an ultrasonic transmitter and a receiver. The transmitter will send out a signal at 40 kHz that will hit some object, most likely a book, and reflect that signal to the receiver. The received signal should have a phase difference from the outgoing signal. Now, when we vary the outgoing signal, the phase shift should also change. Likewise, if we vary the distance to the object, the number of wavelengths that can fit in between the object and the transducers should also change. We would multiply the incoming and outgoing signals and measure the beat signal, but I'm not sure how we would do this in labVIEW. We can calculate the distance to the object by figuring out what d(phase)/d(frequency) is. So far,when I am having problems with actually getting an incoming signal and figuring what that phase shift is. I'm not sure how I could use simulate signal to accuately and precisely send out a 40 kHz sine wave, and then vary that signal by steps of 1 Hz. I have also tried using a signal generator, and having once BNC cable go to the input of the transmitter and the other going to input of the DAQ. I have another BNC cable going from the output of the receiver to the input of the DAQ. I had multiple channels on my DAQ, and used split signals to see the transmitted and received signal. But this doesn't seem to be working. I also tried to add gain to the received signal, but when adding an Op-Amp LF356 to the receiver, the signal completely disappears. Attached are some of the VI's I have, but none of them seem to be working. Thanks in advance for any help.
Attachments:
Latest version of final.vi ‏64 KB
Draft for final project.vi ‏89 KB

Have you done the basic physics and mathematics? For the speed of sound = 343 m/s and the frequency = 40 kHz the wavelength is 8.6 mm. At 40.001 kHz the wavelength is 214 nm shorter.
So, how do you propose to keep track of the number of wavelegnths if the target moves more than 8.6 mm?
To measure a phase shift you must have some kind of reference. Typically a fraction of the transmitted signal is used as a reference. Since you probably do not know how much phase shift occurs in the power amplifier driving the transmitter or between the electrical signal at the transducer and the acoustic signal in air, it is usually best to measure both, ideally with the same receiver and amplifiers.
The LF356 should be good for modest amounts of gain. The transducers can look like a capacitance to the circuits. Do you have a DC offset which is saturating the amplifier?
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How to measure the phase shift using AC analysis?

Hi,
I have a simple RLC circuit consisting of no more than 4 components. If i hook up the network analyser function to the circuit and read the S11 values, i can see a change in the input impedance and a phase shift when i run it across a range of frequencies.
I am trying to do the same with the AC analysis tool. I've placed a probe on the positive input line. Using the AC analysis i've obtained the input impedance by using the expression mag(V(Probe1))/mag(I(Probe1)). Everything looks fine but i just can't seem to obtain the correct expression to gain the phase shift. All of the values i get out seem to flat line.
It would be great help if someone could point me in the right direction, as i'm running out of ideas.
Thanks for the help.
Attachments:
M1.png ‏3155 KB
m2.png ‏618 KB

Hi 08Ultrasound,
You need to measure the voltage phase difference over a load as the voltage source is ideal so will always be in phase.
Regards,
Adam Brown
Applications Engineer
National Instruments UK

Calculation of phase shift

Hi all,
I am continuously acquiring two sinusoidal signals from the analog inputs of a daq card and saving the samples of the two signals into two different float type arrays. Can anyone tell me that how to calculate the phase shift between these two signals and as well as the peak voltage of the two signals? Please expain me with the help of an example code.
Thanks

Hi AI S
I have gone through the example of phase diff e.g and i have written the following code but when i run it , it gives the max value of 1st sine wave (outarray1) nearly equal (i-e 7.7 volt ) but it should be 8 V pk.
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Here is my code
double outarray1[8192],outarray2[8192] ;
double *peakLoc, *peakAmp, *peakDeriv;
    int count;
static double wave1maxval = 0.0;
static int wave1maxind = 0;
static double wave2maxval = 0.0;
static int wave2maxind = 0;
static double phasediff;
PeakDetector (outarray1,8192,0.0, 3, 0, 1, 1, &count, &peakLoc, &peakAmp, &peakDeriv);
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        wave1maxind = peakLoc[0];
        wave1maxval = peakAmp[0];
SetCtrlVal(panelHandle,PANEL_wave1maxind, wave1maxind);
SetCtrlVal(panelHandle,PANEL_wave1maxval, wave1maxval);
    if (peakLoc)
        FreeAnalysisMem (peakLoc);
    if (peakAmp)
        FreeAnalysisMem (peakAmp);
    if (peakDeriv)
        FreeAnalysisMem (peakDeriv);
    PeakDetector ( outarray2,8192,0.0, 3, 0, 1, 1, &count, &peakLoc, &peakAmp, &peakDeriv);
    if (count>0)
        wave2maxind = peakLoc[0];
        wave2maxval = peakAmp[0];
SetCtrlVal(panelHandle,PANEL_wave2maxind, wave2maxind);
     SetCtrlVal(panelHandle,PANEL_wave2maxval, wave2maxval);
    if (peakLoc)
        FreeAnalysisMem (peakLoc);
    if (peakAmp)
        FreeAnalysisMem (peakAmp);
    if (peakDeriv)
        FreeAnalysisMem (peakDeriv);
    phasediff = (8/8192) * (wave1maxind - wave2maxind) * 360;
    phasediff = fmod (phasediff, 360);
   SetCtrlVal(panelHandle,PANEL_Phase_Diff,phasediff);

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Invert
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+display, the wave’s crests become troughs and vice versa.+
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DIAdemTexte.pdf ‏435 KB

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Determine phase shift ben input & output

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