Phase Angle Dephasing in Two time signal FFT

[DaiZheng]

Pardon my English, using "dephasing".

The problem happened with FFT(Two time signal)

1st input channel is /Time

2nd input channel is /SWA (steering wheel angle,it's a Frequency Sweap)

Output channel is /Acc_Y (lateral acceleration)  

The phase angle figure is as following:

The phase angle just changed the sign which is incorrect. The output channel is not ahead of the input.

Phase angle in deg

Following is the time domained graph for input and output.

The output has a delay more than half cycle after  ~2.7 Hz which leads to the sign change

Red is input , green is output

Is there any option to correct that excluding manual correction ?

[altenbach · Accepted solution]

You need to unwrap the phase. Start here.

[DaiZheng]

Thanks a lot , never know this function until your answer :- )