Teledyne 360E Benutzerhandbuch

 

IR 

Source 

IR Beam 

Sample Chamber 

Band-Pass Filter 

Photo-Detector 

Upon exiting the sample cell, the beam shines through a band-pass filter that allows only light at a wavelength of 
4.3 µm to pass.  Finally, the beam strikes a solid-state photo-detector that converts the light signal into a 
modulated voltage signal representing the attenuated intensity of the beam.   

Unfortunately, water vapor absorbs light at 4.3 µm too.  To overcome the interfering effects of water vapor the 
Model 360E adds another component to the IR light path called a gas filter correlation (GFC) wheel (see Figure 
10-2). 

(Pure N

2

)

 

(N

2

 with CO

2

)

 

 

A GFC wheel is a metallic wheel into which two chambers are carved.  The chambers are sealed on both sides 
with material transparent to 4.3 µm IR radiation creating two airtight cavities.  Each cavity is filled with specially 
composed gases.  One cell is filled with pure N

2

 (the measure cell)

.  

The other is filled with a combination of N

2

 

and a high concentration of CO

2

 (the reference cell).