Matlab wavelets feature extraction

[aswathymohan]

Hi How to find out the amplitude and duration of a sine wave of different amplitudes?

Consider a voltage sag ie, a 50hz signal of amplitude less than the normal one.I have to find out the amplitude and duration at wich this disturbance occurs.

I have read some articles which gives some information that we can extract time and frequency information using wavelets db4 using multi resolution analysis .As i am a beginner i have just a rough idea about the work.Can anyone please direct me to accomplish my works and obtain output in matlab?

Thanks

 

[tgootee]

You could just do it directly. If you continuously sampled the waveform (maybe from a voltage divider's output, so it would be in ADC's input range), then you could find each local peak voltage value. You would just compare that value to the threshold you set, to decide if it is below the threshold (i.e. in a "sag" condition).

If you were not already in a sag condition, record the time as the start of a sag, in a sag event log.
If you were already in a sag, just continue.
If you were in a sag but the new peak is above threshold, then record the end of the sag in the event log.

 

[aswathymohan]

Matlab wavelet feature extraction help

How can we extract information from wavelet approximation and detail coeffients .for eg.i hav a voltage sag signal with start time=0.016 and end tim=0.02.How can i determine this duration from coeffients and the magnitude of the signal

my matlab code is

u = inline('t >= 0');
n=1:4
 %waveform generation
fs=250
A=0.7; t1=12; t2=24;
 t = 0:0.1:100
v1=sin(2*pi*(50/fs)*t);

v2=(1-A*(u(t-t1)-u(t-t2))).*sin(2*pi*(50/fs)*t);
figure(1);
plot(v1);
title('Original signal');
Ylabel('s');
figure(2);
plot(v2);
title('Voltage Sag');
Ylabel('s');
[c,l]=wavedec(v2,6,'db6');
a6=wrcoef('a',c,l,'db6',6);
figure(2);
subplot(7,1,1);
plot(a6);
title('Decomposes the sixth layer with dbs=a6+d6+d5+d4+d3+d2+d1');
Ylabel('a6');
for i=1:6
decmp=wrcoef('d',c,l,'db6',7-i);
subplot(7,1,i+1);
plot(decmp);
Ylabel(['d',num2str(7-i)]);
end
A = appcoef(C,L,'db6',6)