This article presents the theory and practice of automatic process control and instrumentation, outlining basic concepts of automatic control. The process control hierarchy is described, as is the role played by modern control systems equipment. Because reliable process measurements form the foundation for automatic process control, devices used to measure basic process variables, as well as the practical guidelines for their selections and implementation, are discussed. On-line process analyzers are also introduced followed by a brief discussion of considerations in the selection and use of final control elements. An overview of the mathematical principles underlying process control is presented and the most common implementations of single-loop feedback controllers are described. This is followed by a discussion of more advanced control techniques. Since most control methods can be applied to continuous as well as batch processes, concepts related to batch process control are introduced. In a final section, economic aspects of process control are discussed.
Kirk-Othmer Encyclopedia of Chemical Technology, 6th edition, John Wiley & Sons, New York (2014)