TRANSFER FUNCTION IN System Identification Toolkit

[Mao85]

Hi,

I try to using signal express and System Identification Toolkit for identify transfer function of a R-C circuit(low pass filter). The thorical function is G(s)=1/1+sRC. But if i calculate this function, according to the characteristics of the circuit elements, I obtain a different results compared to what i get from signal express. I try to read manual of SI Toolkit and follow this example http://www.ni.com/white-paper/4604/en/. but i don't find response. To be sure I also simulated the circuit response in matlab I get the correct results.

Maybe some person who has already used this toolkit it could help me.

This is the result of signal express analysis.

And this is system resonse to the stimulus:

Thanks a lot.

[CBart91 · Accepted solution]

Goodmorning,

I made some test about your configuration. it's not possible to display the transfer function as you desire.

the transfer function can only be displayed in the following form :  G(s) = G(0)(s-z)/(s-p)

the esponential at the left of your formula represent the delay you have selected in Parametric estimation>> model order setting. if you choose 0 delay you will set the esponential to 1.

To display the transfer function as I wrote, you should change some configuration.

Convert to control design model>> control design model type>> Zero-Pole-Gain

Discretize model>>method>>Backward

Best regards

Claudio