Theory of Operation Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 192
9.1.4.1. Ambient CO
2
Interference Rejection
CO
2
absorbs IR light very well. So well that even the narrow volume of ambient air between the IR
source and the sample chamber is enough to alter the analyzer’s measured concentration of CO
2
. Also,
ambient air, which averages around 350 ppm to 400 ppm, will vary significantly over the course of the
day. The ambient CO
2
concentration can rise as high as 1 000 ppm during the time of the day when
people are present. It can fluctuate 300 ppm as the photosynthesis of plant life in the nearby area
increases during the day and decreases at night.
The basic design of the GFC 7000TA rejects most of this interference at a 100:1 ratio; however this still
can allow small fluctuations in CO
2
concentration during the course of the day. To completely remove all
effects of ambient CO
2
from the analyzer’s measurement of CO
2
, dried air, scrubbed of all CO
2
is pumped
into the GFC wheel housing to purge all ambient CO
2
(see Figure 10-7)
