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A Simple Conductimetric CO 2 Analyzer with Automatic Recalibration: I. Design, Implementation, and Functionality
Author(s) -
Acock Basil,
Wall Gerard W.
Publication year - 1995
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1995.00021962008700010012x
Subject(s) - spectrum analyzer , process engineering , carbon dioxide , co2 content , electrical resistivity and conductivity , calibration , analytical chemistry (journal) , environmental science , chemistry , electrical engineering , engineering , mathematics , environmental chemistry , statistics , organic chemistry
Controlled‐environment plant growth cabinets may be used to investigate the long‐term effect of elevated carbon dioxide concentration ([CO 2 ]) on plant growth. Infrared gas analyzers (IRGAs) are normally used to monitor and control [CO 2 ] 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 [CO 2 ] relies on the change in electrical conductivity when CO 2 is dissolved in demineralized water. This work describes the design, implementation, and functionality of an inexpensive conductimetric system for controlling [CO 2 ] in plant growth cabinets. Regressing electrical conductivity against [CO 2 ] over the range 0 to 1000 μL L −1 yields a quadratic response. Calibration drift inherent in the conductimetric CO 2 analyzer requires that each analyzer be recalibrated periodically. Automatically recalibrating with an IRGA every 900 s gave control of the [CO 2 ] within the plant enclosures to within 10 to 15 üL L −1 of the set point. The [CO 2 ] control system is robust enough to maintain this accuracy regardless of the desired [CO 2 ] set point or the mass of plant material within the plant growth cabinet. In this approach, only one IRGA is required to control [CO 2 ] in many plant growth cabinets if each cabinet has a dedicated conductimetric CO 2 analyzer.