Different approaches for relay-based identification and control of unstable processes

Two relay-based techniques for identification and control of chemical processes operating in unstable conditions are presented. The first one (proposed by Park et al. [10]) identifies a first order model and uses a double feedback structure for control, thus ensuring stability for low order process dynamics. The second method requires two relay tests and uses an extension of the ATV⁺ technique (Marchetti and Scali [8, 13]) for a parametric identification of the process.