Gas Filter Correlation; The Gfc Wheel - Teledyne T300 Operation Manual

Teledyne API – Model T300/T300M CO Analyzer
IR
Source

13.2.1. GAS FILTER CORRELATION

13.2.1.1. THE GFC WHEEL

06864B DCN6314
Sample Chamber
IR Beam
Figure 13-1:
Upon exiting the sample cell, the beam shines through a band-pass filter that allows only
light at a wavelength of 4.7 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 4.7 µm too. To overcome the interfering
effects of water vapor the T300/T300M adds another component to the IR light path
called a Gas Filter Correlation (GFC) Wheel.
Figure 13-2:
A GFC Wheel is a metallic wheel into which two chambers are carved. The chambers
are sealed on both sides with material transparent to 4.7 µm IR radiation creating two
airtight cavities. Each cavity is mainly filled with composed gases. One cell is filled
with pure N (the measurement cell)
2
high concentration of CO (the reference cell).
Band-Pass Filter
Measurement Fundamentals
Measurement Cell
(Pure N )
2
Reference Cell
(N with CO)
2
GFC Wheel
The other is filled with a combination of N
.
Theory of Operation
Photo-Detector
and a
2
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