# Shiftet values of omega in bode plot as result from generating idfrd() and tfest()

3 vues (au cours des 30 derniers jours)
Rai Way le 17 Juil 2024
Commenté : Rai Way le 18 Juil 2024
Hello,
i have a problem at the calculation / estimation of a transfer function when using frequency-domain data.
My task is to get the continious transfer function for further simulation from measured magnitude and phase response by an impedance analyser.
The quality of the estimated curve is ok, but the problem is that the curve is shifted in omega and i cannot observe the problem.
The frequency limits of the measured data are 20 Hz to 5000 Hz with the units (freq. [Hz], magn [-], phase [°]).
Figure 1 and Figrue 2 shows the magnitude and phase of the measured data.
In Figure 3 shows the bode plot with idfrd() / frd() and the estimated TF.
Here the values are shiftet.
What ist the problem in this case?
format short g
clear
fre = matt(1:300,1);
abso = matt(1:300,2);
absdb = 20*log10(abso);
phdeg = matt(1:300,3);
% options = bodeoptions;
% options.FreqUnits = 'Hz';
figure(1)
semilogx(fre,absdb)
legend()
ylabel('magn. [dB]')
xlabel('freq. [Hz]')
grid()
figure(2)
semilogx(fre,phdeg)
ylabel('magn. [dB]')
xlabel('freq. [Hz]')
legend()
grid()
tf_estimated = tfest(vect_mess,3)
tf_estimated = 2.637 s^2 + 77.66 s + 337.4 ------------------------------- s^3 + 175.3 s^2 + 1839 s + 3528 Continuous-time identified transfer function. Parameterization: Number of poles: 3 Number of zeros: 2 Number of free coefficients: 6 Use "tfdata", "getpvec", "getcov" for parameters and their uncertainties. Status: Estimated using TFEST on frequency response data "vect_mess". Fit to estimation data: 99.13% FPE: 8.091e-08, MSE: 7.774e-08
figure(3)
bode(vect_mess,tf_estimated )
legend()
grid()
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### Réponse acceptée

Paul le 17 Juil 2024
If fre is in Hz, then this line
should be
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Rai Way le 18 Juil 2024
Oh, oh, oh.
Thank you so much.
No one should tell my professor ;)

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