Process Control: Modeling, Design, and Simulation

3.1. Background

One of the major goals of this chapter is to obtain an understanding of process dynamics. Process engineers tend to think of process dynamics in terms of the response of a process to a step input change. Assume that the process is initially at steady state, then apply a step change to an input variable. The majority of chemical processes will exhibit one of the responses shown in Figure 3-1. In this plot, we assume that a positive step increase has been made to the input variable of interest. The solid curves are examples of “positive gain” processes; that is, the process output increases for an increase in the input. The dashed lines are those of negative gain processes. The curves in Figure 3-1a show a monotonic change in the ...