CO2 monitoring and control system for controlled environment chambers.
1992
Pamplona R.R. | Manalo P.A. | Egeh A.O. | Ingram K.T.
Research on crop growth simulation under future scenarios requires controlled environments. Current research on global climate change and rice at IRRI [Philippines] investigates the effects of increased carbon dioxide (CO2) and temperature on rice growth. A new system was installed to upgrade the existing IRRI Phytotron plant growth chambers. This system is capable of monitoring and controlling CO2 inside temperature and humidity controlled chambers. The CO2 monitoring and control system include six growth chambers, an infrared gas analyzer (IRGA), compressed gas cylinders, light sensor, Superlink Communication software, a 386 desk top computer with printer, and a DGT Vomatic climate computer. The system includes six sunlit glass chambers with 1.2 x 1.2 m square floor space. The climate computer monitors the data and settings, reads the accumulated data, prints statistical reports and graphs, calculates CO2 input requirements from measured CO2 levels and light intensity and commands the control of the climate computer. The climate computer then actuates solenoids for controlling CO2 sampling and injection. Gas samples are continuously delivered to the IRGA with polyethylene tubings. Solenoids route gas to the measuring cell or to an exhaust bypass. Opening of growth chambers and changing conditions due to the diurnal changes in ambient CO2 and light intensity requires sensitivity factor to adjust time of CO2 injection proportionate to the difference between current and desired CO2 concentrations. Preliminary data show an average difference of plus or minus 5 ppm for setting the chamber of 330 ppm (ambient) and plus or minus 30 ppm for 660 ppm. Future modification of the cell model program in the computer will use the proportional integral differential control for more precise regulation of the CO2 level.
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