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Teledyne Analytical Instruments 

187 

The Model GFC 7000TA Gas Filter Correlation Carbon Dioxide Analyzer is a microprocessor-controlled 
analyzer that determines the concentration of carbon dioxide (CO

2

) in a sample gas drawn through the 

instrument.  It requires that sample and calibration gasses be supplied at ambient atmospheric pressure 
in order to establish a stable gas flow through the sample chamber where the gases ability to absorb 
infrared radiation is measured. 

Calibration of the instrument is performed in software and does not require physical adjustments to the 
instrument.  During calibration the microprocessor measures the current state of the IR Sensor output and 
various other physical parameters of the instrument and stores them in memory. 

The microprocessor uses these calibration values, the IR absorption measurements made on the sample 
gas along with data regarding the current temperature and pressure of the gas to calculate a final co

2

 

concentration.   

This concentration value and the original information from which it was calculated are stored in one of the 
unit’s internal data acquisition system (DAS - See Sections 6.7) as well as reported to the user via a 
vacuum florescent display or a variety of digital and analog signal outputs. 

The basic principle by which the analyzer works is called Beer’s Law.  It defines the how light of a specific 
wavelength is absorbed by a particular gas molecule over a certain distance.  The mathematical 
relationship between these three parameters is: 

I = I

o

 e

 

Where:  

 

is the intensity of the light if there was no absorption.   

 is the intensity with absorption.   

 is the absorption path, or the distance the light travels as it is being absorbed.   

 is the concentration of the absorbing gas.  In the case of the Model GFC 7000TA, carbon 

dioxide (CO

2

).   

 is the absorption coefficient that tells how well CO

2

 absorbs light at the specific wavelength 

of interest.   

In the most basic terms, the Model GFC 7000TA uses a high energy heated element to generate a beam 
of broad-band IR light with a known intensity (measured during Instrument calibration.  This beam is