Natural frequency extraction
Natural frequency extraction
(OP)
Hi everyone.
I have the impulse response output of a 2nd order system.
What I did was got the frequency response from the transfer function(2nd order equation) and the peaks of the frequency response represents the natural frequency and I found that the natural frequency from these response are correct.
But the problem is that when I got the frequency response function(FRF) from the impulse response output. The values of frequency corresponding to peak FRF are not matching with the natural frequencies.
I am struck in here from 2 days. Please help me, I would really appreciate ur help.
Thanks.
I have the impulse response output of a 2nd order system.
What I did was got the frequency response from the transfer function(2nd order equation) and the peaks of the frequency response represents the natural frequency and I found that the natural frequency from these response are correct.
But the problem is that when I got the frequency response function(FRF) from the impulse response output. The values of frequency corresponding to peak FRF are not matching with the natural frequencies.
I am struck in here from 2 days. Please help me, I would really appreciate ur help.
Thanks.





RE: Natural frequency extraction
(otherwise it would seem unlikely that you would have a transfer function).
The FRF should be fourier transform (or roughly fft) of the impulse response.
Perhaps you can share more details so we can understand what you've been doing and have a hope of figuring what might be wrong
=====================================
(2B)+(2B)' ?
RE: Natural frequency extraction
yes i am working in matlab. I used an example and created 2nd order system. The transfer function is for that 2nd order system.
I got the impulse response for that system.
I used FFT to convert it in to FRF.
I have attached the file for the response that I got with the FRF. It is clear from that file that the frequency of corresponding peak magnitude is not equal to natural frequencies. The most left hand side of the figure has the natural frequencies.
RE: Natural frequency extraction
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Natural frequency extraction
What do u meant by bin number?
Do u mean the left most side of the figure?
The left most side of the figure represents the natural frequency.
I got those values by theoretical analysis. I have verified those values too, they are correct.
RE: Natural frequency extraction
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Natural frequency extraction
nat1 there represents natural frequency.
Does peak value of magnitude FRF represents natural frequency.
Thanks.
RE: Natural frequency extraction
Y1_1=Y2(:,1);
fft1=fft(Y1_1);
fft2=abs(fft1);
figure;
plot(fft2);
axis([0 1000 0 80e-03]);
you are plotting the array fft1 against the array index (ie the bin number), not the frequency
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Natural frequency extraction
Should i take
f=1/t;
and plot(f,fft2).
Are you suggesting that this might help.
I tried this Greg. That did not help.
RE: Natural frequency extraction
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Natural frequency extraction
I can do that.
But am i going in a correct way to get natural frequency from impulse response.
RE: Natural frequency extraction
Time=6500;
Y1_1=Y2(:,1);
N=length(Y1_1);
k=0:N-1;
T=N/Time;
freq=k/T;
X=fft(Y1_1);
plot(freq,abs(X));
The only problem is the rate that is 6500. I took this value with out any calculation. I guessed a value and took it. Can I know how can we get that rate.