Letters Comments on simple control method for integrating processes with long deadtime

In the above-mentioned paper [J Process Control 12 (2002) 391], the authors claimed that the proposed method is a simple and new controller for plants with an integrator and long deadtime that solves some of the draw-backs of previous works. Although the presented results are correct, they do not take into account that several papers have been previously published given the same (and in some cases better) solution for the stated problem. Furthermore, the proposed control structure is internally unstable and cannot be implemented using the suggested block diagram. This note points out that the controller proposed in the commented paper is a particular case of the one presented in IEEE T.A.C. 44(8) (1999) 1597.