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All process investigations should start by a determination of the process model. The modeling strategy used will influence the value of the model parameters, which will in turn affect the controller values determined from tuning rules. This paper will describe an analytical method to identify a model of the dynamic characteristics of a process with a delay by using a tangent and point method, as originally suggested by Murrill, 1967. The methodology has been applied to eight benchmark transfer functions suitable for testing PID controllers, as suggested by Åström and Hägglund, 2000. The main advantages of the modeling approach are that it is simple and it will give more accurate, repeatable results than one based on the more traditional graphical approach.
Zhang, Yue and O'Dwyer, Aidan : Estimation of the parameters of a delayed process using open loop time domain techniques. Proceedings of the 4th Wismarer Automatisierungssymposium, Wismar, Germany, September 22-23, 2005.