Two-Point Characterization of FOPDT Process Response

Corripio reviewed the two-point Smith method for characterizing the open-loop process variable response to a step change in controller output by an apparent dead time, ADT, and an apparent first-order time constant, TFO. The two data points on the process variable response curve are taken at 

3 and T63.2. The data taken are the time elapsed after the step change in controller output for the process variable to reach 28.3% and 63.2% of the steady-state change. The ADT and TFO are calculated from Equations 10.3 and 10.4  

Using Equations 10.2 and 10.3 for the case with T] = 22 and 7 = 0, the calculated first-order time constant is TEO = 1.5(23.7 

Many different tuning rules have been published for estimating the controller tuning parameters to use for a first-order plus dead time (FOPDT) process response, and they are too numerous for a complete review in this book. Only a few will be presented. 

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