ABSTRACT
This chapter devotes to explicitly stating the design objectives in terms of the performance criteria, hence developing quantitative measures of closed-loop performance, which allows to compare alternative controller designs. It focuses on the time-domain specifications; however, they also present some ideas on how to use frequency-domain specifications. In general, the time-domain specifications deal with important properties of the system dynamics, such as the speed of response and the response accuracy or allowable tracking error. To make plantwide control less tedious, recent contributions made it possible to perform automated tuning of controllers (autotuning). Recall the Ziegler–Nichols technique where a proportional-only controller is used to take the closed-loop system close to the stability limit, yielding the ultimate gain. The autotuning method is applied to the level control in a separator which is part of an LNG plant. In addition, the chapter offers a brief discussion on autotuning and demonstrated its application with an example.
