Chapter I Principles of Automatic Measurement and Control of Fermentation Growth Parameters

Abstract

Publisher Summary This chapter presents a discussion on the principles of automatic measurement and control of fermentation growth parameters. The past decade has seen the introduction of automatic measurement-record-control techniques into microbiological work, and it is apparent that the use of these techniques will increase rapidly. The factors discussed in the chapter are general and apply equally well to pH, temperature, dissolved oxygen tension (DOT), redox potential, and so on. The principal factors to be considered in the assessment of measuring and recording instruments are accuracy, reproducibility, long term stability, reliability and robustness. There are two main categories of instruments with electrical inputs—those operating on a “direct-measurement” principle, and those on a “null-point” principle. Automatic control of a variable in a process is most commonly achieved using a “closed loop” control system. The principle of closed loop control is presented, which shows a system for the control of pH in a stirred fermenter. A very important factor influencing the speed of response of a primary element is the turbulence of the fluid surrounding the element. The accuracy of a measuring means can be assessed in terms of four main characteristics: static error, reproducibility, dead zone, and dynamic error. Multipoint control is suitable for controlling temperature in both batch and continuous fermentations and for controling pH in continuous fermentations.