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True Digital Control of carbon dioxide in agricultural crop growth experiments

Research output: Contribution in Book/Report/ProceedingsConference contribution


Publication date1996
Host publicationInternational Federation of Automatic Control 13th Triennial World Congress
Original languageEnglish


The paper outlines the design of Proportional-Integral-Plus (PIP) controllers for regulating the level of carbon dioxide in a closed loop apparatus used for carbon-11 tracer experiments in plants. The system, which behaves essentially as an integrator with a four sample time delay, is quite difficult to control using conventional methods because of the rather limited pulse-width-modulated input signal. In contrast, optimal PIP designs, which exploit a special Non-Minimum State Space (NMSS) form within a Linear Quadratic (LQ) optimisation context, are able to maintain the gas concentration to within 2 ppm of the set point.