A SIMPLE CONDUCTIMETRIC CO2 ANALYZER WITH AUTOMATIC RECALIBRATION .1. DESIGN, IMPLEMENTATION, AND FUNCTIONALITY

Controlled-environment plant growth cabinets may be used to investigate the long-term effect of elevated carbon dioxide concentration ([CO2]) on plant growth. Infrared gas analyzers (IRGAs) are normally used to monitor and control [CO2] in plant cabinets. With many cabinets in use, however, it soon becomes impractical to purchase an individual IRGA for each cabinet, A more economical method of monitoring and controlling [CO2] relies on the change in electrical conductivity when CO2 is dissolved in demineralized water, This work describes the design, implementation, and functionality of an inexpensive conductimetric system for controlling [CO2] in plant growth cabinets, Regressing electrical conductivity against [CO2] over the range 0 to 1000 mu L L(-1) yields a quadratic response. Calibration drift inherent in the conductimetric CO2 analyzer requires that each analyzer be recalibrated periodically. Automatically recalibrating with an IRGA every 900 s gave control of the [CO2] within the plant enclosures to within 10 to 15 mu L L(-1) of the set point, The [CO2] control system is robust enough to maintain this accuracy regardless of the desired [CO2] set point or the mass of plant material within the plant growth cabinet, In this approach, only one IRGA is required to control [CO2] in many plant growth cabinets if each cabinet has a dedicated conductimetric CO2 analyzer.