Obtaining a collection of EXACT full wave cycles of AC voltage

[Henrik_Volkers]

here is a quick draft of another way:

use tone detection to get the exact frequency (in case you don't know it exactly)

calc 10 times the periode length and cut 🙂

things to add

-by using the phase information you can even cut at about the zero crossing....

-narrow the search

-define how to round the 10 periodes point length

However it would be better to know WHY you need 'exactly' 10 periodes (you can resample your data to always get 10 periodes into exaclty N-samples....)

 Edit: didn't saved default values.... choose apprpriate 😄

[TooEagerToLearn]

Thanks Henrik!

I just picked 10. What I wanted to know if to extract samples that relate to an INTEGER number of FULL WAVE CYCLES.

[Henrik_Volkers]

Seems that you want to do some power calculations....

the tone detection vi I used is nice to find a sine frequency information,  for power factor calculations with SMPS it migth not be correct. (If you look narrowband (sine) you are blind to harmonics)

Zimmer aka ZES have some good papers on power (quality)  calculations   and there is also a LabVIEW Addon IIRR.....

If you use a PXI system with a generator for your measurements, make shure they run with the same time base 😉

a FULL WAVE CYCLE doesn't have to start at zero 😉

[TooEagerToLearn]

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@Henrik_Volkers wrote:

Seems that you want to do some power calculations....

the tone detection vi I used is nice to find a sine frequency information,  for power factor calculations with SMPS it migth not be correct. (If you look narrowband (sine) you are blind to harmonics)

Zimmer aka ZES have some good papers on power (quality)  calculations   and there is also a LabVIEW Addon IIRR..... I looked for IIRR and it doesn't show up on NI website.

If you use a PXI system with a generator for your measurements, make shure they run with the same time base 😉

I am just using PXI digitizer to read voltage and current. They are sine waves with some noise.

a FULL WAVE CYCLE doesn't have to start at zero 😉

That makes my job even harder. 😞

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Once I find integer number of cycles, My power calculation will be more accurate. Does using AC-DC Estimator that outputs TOtal RMS power be better or using RMS vi?

[Henrik_Volkers]

IIRR  If I Remember Rigth  😄

The ZES paper deals with windowing etc.   at least it's shurely well ( or 'Well, it should be...' ) defined in the standards......

http://www.zes.com/en/Service/Downloads/Documents/Application-Notes

repositorium.sdum.uminho.pt/bitstream/1822/1864/1/ISIE-03_JLA.pdf

[Nathan-P]

There is also the Jitter Analysis Toolkit, which includes a RMS function, which will calculate the RMS values for full wave cycles.  Basically it finds all the zero crossings, and calculates the RMS voltage between all of them, from what I remember. 

http://sine.ni.com/nips/cds/view/p/lang/en/nid/210565