Deadtime Modeling for First Order Plus Dead Time Process in a Process Industry

In this present work consistency of thick stock varying between 2.5%-3.5% in the wet end machine has been chosen for its operation and control. Normally, it gives a first order with dead time response and therefore it is an important candidate for performing the modeling of dead time for further analysis. The dead time expression involves an exponential term in the transfer function and to handle dead time in Laplace domain, it is customary to use approximations for the dead time expression. The Pade approximation is very useful in control analysis in this aspect. In this paper, dead time modeling analysis for an important parameter of paper mill, i.e. consistency is performed using MATLAB software with unit step response for different orders of Pade approximations viz first, fifth, tenth, fifteenth and twentieth order.. The response results are analyzed, compared and important conclusions are derived. Further, it is shown that the higher the order of the approximation used, the more accurate it is at higher frequencies, but at the expense of increased complexity.