09-04-2018 03:56 AM
@bseguin wrote:
At this point, just ignore the phase shift because phase shift will be relevant only if you compare with another signal.
Benoit
but i need to let suppose i want to know the exact phase shift in a signal i am acquiring how would i know that?
let suppose there is a signal that have zero phase shift i acquire that through daq but i am getting some virtual phase shift so how can i correct that?
09-04-2018 04:03 AM
OK I think you have a logical problem.
Let's say that you are taking a race.
To find who is the winner, you need to compare at least to runner.
If there is only one runner, how can you know witch one arrive first?
A phase in signal is used only to compare between two signals. Per example a cos signal and a sin signal are exactly the same if they have the same amplitude and the same frequency. You will never know the difference unless you know the time 0.
So to go back to your particular application, Ignore the phase shift if you acquire only one signal since you don't know when it start.
when you will measure the current signal and the voltage signal, then you will be able to compare them and put a phase shift measurement between them.
***VERY IMPORTANT***
But this measurement will be valid only if the acquisition start at the same time for both signal.
Like the two runner, if they do not start at the same time, you cannot tell witch one if the winner.
Benoit
09-04-2018 04:13 AM
@bseguin wrote:
OK I think you have a logical problem.
Let's say that you are taking a race.
To find who is the winner, you need to compare at least to runner.
If there is only one runner, how can you know witch one arrive first?
A phase in signal is used only to compare between two signals. Per example a cos signal and a sin signal are exactly the same if they have the same amplitude and the same frequency. You will never know the difference unless you know the time 0.
So to go back to your particular application, Ignore the phase shift if you acquire only one signal since you don't know when it start.
when you will measure the current signal and the voltage signal, then you will be able to compare them and put a phase shift measurement between them.
***VERY IMPORTANT***
But this measurement will be valid only if the acquisition start at the same time for both signal.
Like the two runner, if they do not start at the same time, you cannot tell witch one if the winner.
Benoit
i am uploading a picture of what i am doing. i am sorry right now i am not at my work bench so i can send you the vi i hope it will give you an idea.
09-04-2018 04:19 AM
You generate a signal with the DAQ or only input?
Benoit
09-04-2018 04:21 AM
@bseguin wrote:
You generate a signal with the DAQ or only input?
Benoit
i am generating signal through function generator, acquire through daq. in the pic the sine generatior is the sinewave generate vi whic i used for reference.
09-04-2018 04:29 AM
As I explained above, If you have two signal, you will need two DAQ that are starting the acquisition exactly at the same time. Then using zero crossing detection of amplitude detection, you will be able to compare the difference of the time between them and knowing the frequency, the phase difference will be easy to calculate.
The virtual phase shift that you see is not real... It is impossible to compensate without reference. If you really create an artificial reference, just detect the zero crossing and determine that this is your zero point. but careful... when you will compare the two signal together, you cannot use the artificial reference. you need to use one signal as reference and compare the other one.
If you do not understand any of the explanation above, I suggest you to go back to the first step... understanding the phase detection BETWEEN signals.
Benoit