[moved] how to measure phase difference in matlab?

[HI12345]

Hi all

I just got the graphs of current and voltage from the NI device.
I want to measure the phase difference between them.
And, I have a program to measure the phase difference, but I don't know how to import my graphs into the program.

Thanks

 

[barry]

A "graph" is visual representation of data. When you say you are trying to "import my graphs" do you really mean you are trying to import data from an NI system into matlab? What is the format of that data? Is it compatible with Matlab? Is it ASCII text?

 

[HI12345]

I import the excel file into Matlab.
However, the phase angle is too small and it shows zero degree.

 

[barry]

Well, you've got two choices:
1) Your phase angle is, in fact, very small.
2) Your calculation is wrong.

Did you plot your data in Matlab? Does it look the same as it does in NI?

Your initial post says you didn't know how to import your data, now you say 'the phase angle is too small'. You don't really give a lot of information. Is your problem actually that your Matlab program is not working properly?

 

[HI12345]

Sorry for giving too little information.
I did plot my data in matlab and it looks same as NI showed
My phase angle is very very small which is about 0.05 degree
However, I have to calculate the phase angle by using an algorithm

 

[FvM]

To determine a phase angle, you have to know the signal period.

 

[barry]

Sorry for giving too little information.
I did plot my data in matlab and it looks same as NI showed
My phase angle is very very small which is about 0.05 degree
However, I have to calculate the phase angle by using an algorithm

So, what is your problem? How do you know your phase angle is 0.05 degrees? Is that the physical reality? Is your sampling system precise enough to measure this? Is this a computation problem? A measurement problem?