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unit of y scale in waveform graph in labview for FFT (not power spectrum)

Hi 

 

 

I am capturing the waveform from agilant 5054 DSO to perform FFT and to calculate the THD+N .

So i captured the waveform and used "SINAD analyzer" vi to find THD+N. But it is giving THD+N as 1.423. To get in %, we have to multiply with 100 (this thing is mentioned in the "help window"). Then it will be 142% which is impossible.

 

 

So i want to know what is the unit in which the THD+N value is displayed on the front panel after using the "SINAD analyzer" VI ???

 

 

 

Thank you

 

 

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Please post your VI with some typical data saved as default. 

 

The output of the FFT VI is in the same units as the input. Search the LV help for "Output Units for FFT-Based VIs" to get more information about units.

 

The SINAD Analyzer uses FFT internally. It looks at three points to find an interpolated peak for the frequency and amplitude.  Are you using Advanced Search to limit the frequency range?  With a very small fundamental and large noise and interferring signals I can get SINAD Analyzer to return values greater than one (but only by a few parts per million).

 

Lynn

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