how to calculate phase shift between two sine wave signals, implementing embedded c

[veerubiji]

I two sinewave signals with same frequency. I want to measure phase shift between two signals. There will be a small phase difference between two signals. I am using ATmega32-A micro controller and external ADC AD7798 to read the voltage of both signal. I am able to read both signal voltages using SPI communication. How to find Phase difference between two sine signals. I am using CodeVisionAVR compiler.

I know that phase shift between two signals can be find out using the fallowing formula.

    A(t)= Am sin(Wt+/-theta).

I know only amplitude(Am) and w =2*pi*f. But How to calculate phase difference between two sinewave signals with knowing amplitude and frequency. Any suggestions please.

 

[barry]

You could measure the time difference between the zero-crossing of the two signals. (You would also have to pay attention to the slope of the signals at the zero cross as well). Then the phase difference would be:

(360 degrees/period)*time difference

 

[jeffrey samuel]

That formula alone is enough then Barry why is there a need for slope to be considered here

 

[veerubiji]

You could measure the time difference between the zero-crossing of the two signals. (You would also have to pay attention to the slope of the signals at the zero cross as well). Then the phase difference would be:

(360 degrees/period)*time difference

Can anyone explain me how to calculate time difference between the zero-crossing of the two signals. Any algorithm or procedure? Because I am just reading the both signals amplitude using ADC and i know the frequency. How to calculate time difference?

 

[jeffrey samuel]

The point where the ADC op is 0V that point is the zero point comparing the op of the ADC will suffice you

 

[veerubiji]

The point where the ADC op is 0V that point is the zero point comparing the op of the ADC will suffice you

I am able to read ADC value when output is 0V, then I can read when it is maximum. But how to measure time difference. I didn't understand the concept really. That is why I have asked like that.

 

[jeffrey samuel]

Since discrete entries are only sampled by the ADC 's at the same time Use a counter that gets initialised to 0 when the first ADC op is 0 till the time the second ADC points to 0

Also consider the Slope of the curve they must be same other wise an error of 180 deg is possible

 

[barry]

Ok, here's an algorithm:

Sample the first signal
When the signal crosses zero with positive slope, initialize a counter
Now sample the second signal
When the second signal crosses zero with positive slope, stop the counter. The counter now contains a value proportional to phase difference

 

[veerubiji]

Hi ,

I am using external ADC to signal voltage. I am selecting input or output signal through MUX (multiplexer). I can read only one signal at a time.

- - - Updated - - -

Thanks for the algorithm, Now I will try to implement.

 

[veerubiji]

Can any one suggest me which is the best method to calculate the phase shift between two signals with same frequency 250KHz.

I am selecting input and output signals through multiplexer. I want to calculate phase shift between input and output signals.

After selecting signal through multiplexer, the signal is passing through demodulator. I am getting demodulator output as D.C signal with max peak voltage of multiplexer output(Sinewave)signal.I am reading that signal using ADC.

Can I calculate phase shift using software without adding any hardware? If not possible with software then suggest me any other way? I am using CodeVision AVR compiler.

 

[barry]

Sense makes this not.

1) What kind of 'demodulation' is occurring?
2) You are sampling two DC signals which are proportional to magnitude, DC SIGNALS HAVE NO RELATIVE PHASE SHIFT!!