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how to measure a FFT of 50Hz signal?

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Mudasir Ahmed
Mudasir Ahmed 2016-11-27
评论： Walter Roberson 2016-11-28
hi
I want to measure the FFT of 50HZ signal. I collect the data from oscilloscope which is also attached herewith. the total sample points are 10000. I need the FFT in bar graph as like in attached picture ( mag (% of Fundamental) vs Harmonic Order )but I am unable to do this. kindly help me I will be highly thankful to you.
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Walter Roberson
Walter Roberson 2016-11-28
Looking through the data, I can see that the times given are stored to only two digits after the decimal place, which is a problem because at the initial range the change is all in the third decimal place. You would be better off ignoring the times and re-synthesizing them knowing they are 1E-5 apart.
Walter Roberson
Walter Roberson 2016-11-28
"but the sampling rate is 10KHZ"
Your timestamps do not make any sense unless the data points are 1E-5 apart, which corresponds to 100 kHz not to 10 kHz.

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回答（1 个）

Image Analyst
Image Analyst 2016-11-27
Did you use fft() or pwelch()? If not, why not? If you did, what did you do? Where is your code?
  2 个评论
Mudasir Ahmed
Mudasir Ahmed 2016-11-27
编辑：Walter Roberson 2016-11-28
dear sir,
first I load excel file in Matlab. then I give the command
[R, HARMPOW, HARMFREQ] = thd(signal,10000,100) ;
then I convert harmonic power in percentage
h=100.*(10.^(HARMPOW/20));
t=1:1:100
bar(t,h)
but the graph does not look like as attached in a picture.
Walter Roberson
Walter Roberson 2016-11-28
The graph uses 40 harmonics separated by 1/2 rather than 100 harmonics separated by 1.
Also as I indicated above, your sampling frequency is surely 100000 rather than 10000 .

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