Re: Electrical signal analisis

[Joe Koski]

There are two more signal processing libraries (besides those with octave
and octave-forge) of which you should also be aware, and possibly install.
The URLs for them are

http://www-stat.stanford.edu/~wavelab/
http://wiki.octave.org/wiki.pl?WavelabOnOctave

And 

http://iut-saint-nazaire.univ-nantes.fr/~auger/tftb.html
http://perso.ens-lyon.fr/patrick.flandrin/emd.html

The latter has a routine extr.m that finds all local maxima and minima of a
time (or frequency) series.

For help with octave and octave-forge signal processing routines, check the
information at 

http://octave.sourceforge.net/index/index.html

There is a wealth of good signal processing software available. Good luck.

Joe Koski

on 8/17/04 7:10 PM, Jaime Alberto Silva at address@hidden wrote:

> I'm new in the use of this tools (octave, mathlab, etc.) and since I'm a
> full time Linux user I am using octave.
> 
> Currently, I'm trying to do some electrical signal analysis and I will
> like to know if there are predefined functions for some calculations or
> how can I do them with octave:
> 
> 1. Frecuency: I have founded in the "Signal Processing" section the fft
> function, OK it is great but how do I find the frecuencies from the
> returned vector. I know that using the max function I can find the
> fundamental frecuency like this:
> 
> # Create the signal:
> octave:190> t= [0: 1/2000: 5 - 1/2000];
> octave:191> sint= sin(2*pi*60*t);
> # Transform the signal:
> octave:192> ft= abs(fft(sint));
> # Find the position of the max value of the transformation:
> octave:193> [val, idx]= max(ft);
> # Use the sampling rate to obtain the fundamental frecuency:
> octave:194> fund_frec= 2000 * idx/ length(ft)
> fund_frec = 60.200
> octave:195>
> 
> But how can I find the other frecuencies in case it has more components
> like in
> f= sin x + 0.5 sin 3x + 2 sin 10x ?
> 
> 2. Phasors: If I have 2 signals like v1 an v2 how do I find the angle of
> v2 with respect of v1. I mean if v1= sin (t) and v2= sin (t + 15°) and I
> have sampled those signals in time, how do I find that v2 is delayed 15
> degrees with respect to v1? taking in account that v2 samples where
> taken in different times to v1 samples like this: v1(1) was taken at T0,
> v2(1) was taken at T0 + dT. And, of course, you know the value of dT.
> 
> 3. Electric Power: If I have sampled the signals of voltage (V) and
> current (I) are there any tools that l can use to obtain the active (P)
> and reactive (Q) power, the S vector angle, etc. ? I know that I can
> multiply the signals but, you know if there are tools for that why do it
> again.
> 
> Thanks in advance for any help you can bring me.



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