A SIMPLE CONDUCTIMETRIC CO2 ANALYZER WITH AUTOMATIC RECALIBRATION .3.DYNAMIC-RESPONSE

Conductimetric CO2 analyzers provide an economical means of monitoring and controlling carbon dioxide concentration ([CO2]) in plant growth cabinets. When conductimetric CO2 analyzers are being used to measure canopy CO2 uptake over a period and compare that with light received, it is essential to know the time between an air sample leaving the can opy and its [CO2] being registered by the analyzer. A four-way analysi s of variance in three replicates of a split split-plot design was use d to examine the response time of the conductimetric CO2 analyzers to successive step changes in [CO2] (Delta[CO2]) from 200 to 400, 600, 80 0, and 1000 mu L L(-1), at temperatures of 10, 20, 30 and 40 degrees C , at air flows rates of 540 1880 and 3700 mm(3) s(-1), and at water ho w 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 CO2 analyzers, with response time m eans ranging from 99 to 145 s. Each analyzer, therefore, is unique and must be recalibrated following a change in any one component. A signi ficant water flow rate x temperature interaction was observed (respons e time means ranged from 86 to 177 s). Comparing these response time m eans to the 900-s sampling period indicates that an individual conduct imetric CO2 analyzer will adjust to the new steady state following a c hange 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 t he CO2 control set point for the plant growth cabinet is made. This da ta loss is acceptable.