question about harmonic analysis

[knifeman]

My OS is LabVIEW 8.0. I want to analysis the harmonic containing in a waveform which I get from the signal source through the DAQ card. It is all OK until the next step FFT!

Signal source create a 50Hz, the amplitude is 1 square waveform and LabVIEW has received it successfully went with a error. The FFT result should be amplitude=1,dB=0 at the 50Hz point. The fact is amplitude=0.9040,dB=-0.8764 (I create a program to write the result in .mat format file and use Matlab to check it), and the front panel is given bellow. And the 061126_*.mat is the exactly data and

[crelf]

Please upload your code so we can comment.

[Neville D]

My OS is LabVIEW 8.0. I want to analysis the harmonic containing in a waveform which I get from the signal source through the DAQ card. It is all OK until the next step FFT!

Signal source create a 50Hz, the amplitude is 1 square waveform and LabVIEW has received it successfully went with a error. The FFT result should be amplitude=1,dB=0 at the 50Hz point. The fact is amplitude=0.9040,dB=-0.8764 (I create a program to write the result in .mat format file and use Matlab to check it), and the front panel is given bellow. And the 061126_*.mat is the exactly data and

[crelf]

A step change can only be represented by infinite number of sine waves of different frequencies.

Great to see some physics being brought into the equation knifeman - can you at least upload some of your raw data? Then we can check out if it's appropriate for harmonic analysis.