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A Simple Conductimetric CO 2 Analyzer with Automatic Recalibration: III. Dynamic Response
Author(s) -
Wall Gerard W.,
Acock Basil
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/agronj1995.00021962008700010014x
Subject(s) - spectrum analyzer , carbon dioxide , chemistry , analytical chemistry (journal) , gas analyzer , environmental science , sampling (signal processing) , volumetric flow rate , nitrogen , chromatography , environmental chemistry , thermodynamics , optics , physics , organic chemistry , detector
Conductimetric CO 2 analyzers provide an economical means of monitoring and controlling carbon dioxide concentration ([CO 2 ]) in plant growth cabinets. When conductimetric CO 2 analyzers are being used to measure canopy CO 2 uptake over a period and compare that with light received, it is essential to know the time between an air sample leaving the canopy and its [CO 2 ] being registered by the analyzer. A four‐way analysis of variance in three replicates of a split split‐plot design was used to examine the response time of the conductimetric CO 2 analyzers to successive step changes in [CO 2 ] (∆[CO 2 ]) from 200 to 400, 600, 800, and 1000 μL L −1 , at temperatures of 10, 20, 30, and 40°C, at air flows rates of 540, 1880, and 3700 mm 3 s ‐1 , and at water flow rates of 1.0, 0.66, and 0.33 mL s −1 . Response times ranged from 30 to 542 s across all treatments. Significant differences were observed between individual conductimetric CO 2 analyzers, with response time means ranging from 99 to 145 s. Each analyzer, therefore, is unique and must be recalibrated following a change in any one component. A significant water flow rate ✕ temperature interaction was observed (response time means ranged from 86 to 177 s). Comparing these response time means to the 900‐s sampling period indicates that an individual conductimetric CO 2 analyzer will adjust to the new steady state following a change in control within 9.5 to 20% of the sampling period. Only 1 data record out of 96 within a diurnal cycle is lost if an alteration in the CO 2 control set point for the plant growth cabinet is made. This data loss is acceptable.