Parameter estimation of an unstable process in the frequency domain

The parameters of an unstable delay type process are estimated in the frequency domain. The independence of the Fourier transform amplitude to time delay changes and the Levi method (1959) are utilized to obtain explicit expressions for the parameters. We further use the controller settings data to reduce the influence of disturbance and noise on the parameter estimation. The proposed method is applicable to both under and over-damped closed loops.