IR Source
The IR source emits broadband infrared radiation that irradiates the filter in the correlation wheel.
Figure 9 – IR Source
Gas Filter Correlation Wheel Assembly
The gas filter correlation wheel contains three segments: a N
2
filled sapphire chamber, a CO filled
sapphire chamber and a mask.
The N
2
chamber allows all the IR radiation to pass through, which allows the radiation to
be absorbed by CO in the measurement cell and readings to be recorded.
The CO filled chamber absorbs wavelengths sensitive to CO. The sample gas (containing
CO) in the measurement cell does not receive CO specific IR radiation and the only
detected signals registered by the IR detector are from background sources and
interference.
The mask blocks all IR light entering the cell. This allows the intensity of the other two
signals to be corrected for the detector response to no IR radiation.
Figure 10 – Gas Filter Correlation Wheel Assembly
Opto-Detector
The correlation wheel has four tabs that act as an opto electronic switch ensuring that the main
controller PCA can determine accurate timing of the wheel and the segment currently exposed to the
IR radiation.
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