Teledyne M300EM operation manual The GFC Wheel

Teledyne API – Technical Manual - Model 300E Family CO Analyzers Theory of Operation

11.2.1.1.The GFC Wheel

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 N2 (the measurement cell). The other is filled with a combination of N2 and a high concentration of CO (the reference cell).

IR unaffected by N2 in Measurement Cell

IR is affected by CO in Reference Cell

IRM

Source

R

GFC Wheel

Δ H

Photo-Detector

Figure 11-3: Measurement Fundamentals with GFC Wheel

As the GFC Wheel spins, the IR light alternately passes through the two cavities. When the beam is exposed to the reference cell, the CO in the gas filter wheel strips the beam of most of the IR at 4.7μm. When the light beam is exposed to the measurement cell, the N2 in the filter wheel does not absorb IR light. This causes a fluctuation in the intensity of the IR light striking the photo-detector which results in the output of the detector resembling a square wave.

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