Titration Curve Estimation for Adaptive pH Control

High performance pH control requires a good model of the titration curve, whih the described the nonlinear gain of the process. In many applications, the titration curve changes significantly over short periods of time, and some form of online titration curve estimation is essential. Unfortunately, the titration curve is a complex nonlinear function of process composition, and direct estimation of its parameters is difficult. This paper presents an estimation technique which uses as parameters a basis set of entire titration curves. The parameter choice linearizes the estimation problem, and has proven flexible and robust. An adaptive pH controller is described that uses the estimation technique to identify a process model online, and uses the model to provide a gain schedule for a PI controller. Results of pilot plant testing of this controller are presented.