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???
11/08/06 06:29
Modified:
  11/08/06 06:49
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 		 #127535 - Re: Analogue method.
Responding to: ???'s previous message
Dear Steve,

Thanks for your reply, the analog method you suggested looks good, but in my application I dont intend to change any hardware. I want to do it all digitally. I have 12 bit 500 samples per cycle and want to compute THD directly using these samples without any analog.

After reading your reply, I got a new idea. I have 500 instantaneous values over a cycle. i can compute RMS value of signal then using this RMS value caculate 500 instantaneous values of pure sine wave. then subtract my measured values from these calculated pure sine wave instantaneous values. Finally compute RMS of the diffrence and this should be THD of waveform am I right?

Thanks & Regards,
Prahlad Purohit

List of 32 messages in thread
TopicAuthorDate
Measuring THD [ Total Harmonic distortion ]            01/01/70 00:00      
   ANalogue method.            01/01/70 00:00      
      Re: Analogue method.            01/01/70 00:00      
         fundamental flaw?            01/01/70 00:00      
            Re: Fundamental Flaw.            01/01/70 00:00      
               Digital filter            01/01/70 00:00      
                  Re: Fundamental Frequency.            01/01/70 00:00      
               FFT            01/01/70 00:00      
                  mains frequency            01/01/70 00:00      
                     Why rely on an assumption?            01/01/70 00:00      
                  Re: FFT            01/01/70 00:00      
                     FFT            01/01/70 00:00      
         What use?            01/01/70 00:00      
   Goertzel filters, maybe ?            01/01/70 00:00      
   FFT is the first choice            01/01/70 00:00      
      Is it?            01/01/70 00:00      
         If you know the fundamental.            01/01/70 00:00      
            Re: Fundamental            01/01/70 00:00      
               Multiple cycles            01/01/70 00:00      
                  The 50Hz fundamental must dominate            01/01/70 00:00      
               Fundamental and harmonics!            01/01/70 00:00      
                  Re: Fundamental and harmonics.            01/01/70 00:00      
                     You're getting into theory            01/01/70 00:00      
                     That is very simple!            01/01/70 00:00      
         I think, yes            01/01/70 00:00      
   Alfredos Code Doesnt seem to work properly.            01/01/70 00:00      
      Do you want it to write in "C"?            01/01/70 00:00      
         Yes Kai,            01/01/70 00:00      
      Eh? Endian issue.            01/01/70 00:00      
         Tags            01/01/70 00:00      
   How about this method for THD.            01/01/70 00:00      
      Mix of numerical calculation and FFT            01/01/70 00:00      

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