In the design of IMC controller or other robust controller for robust performance in process control application, one of the necessary conditions is model (or process) uncertainty bound. The method of calculating model (or process) uncertainty bound for the first order lag process with dead time (FOPDT) in the robust controller design is reported in literatures. Up to the now, however, no any analytical method of calculating model (or process) uncertainty bound can be used in the second order lag process with dead time (SOPDT). Therefore, the design of the IMC controller for robust performance used to SOPDT also can not be simply achieved.By using first order Pade approximation for the dead time,an analytical method of calculating model (or process) uncertainty bound for SOPDT in the robust controller design is given for the first time.By using this bound, IMC controller design for robust performance can be made satisfactorily.
