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Teledyne Analytical Instruments 

192 

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)