Filter
Top Products
THEORY OF OPERATION Model 360E Instruction Manual
IR unaffected by N
2
in Measurement Cell of
the GDC Wheel and no additional CO
2
in
the Sample Chamber
IR affected by CO
2
in Reference Cell
with no interfering gas in the Sample
Chamber
IR shinning through Measurement Cell of
the GDC Wheel is reduced by additional
CO
2
in the Sample Chamber
IR shining through Reference Cell is
also reduced by additional CO
2
in the
Sample Chamber, but to a lesser extent
M/R
is reduced
CO2 REF
CO2 MEAS
Figure 10-4: Affect of CO
2
in the Sample on CO2 MEAS & CO2 REF
Once the Model 360E has computed this ratio, a look-up table is used, with interpolation, to linearize the
response of the instrument. This linearized concentration value is combined with calibration SLOPE and
OFFSET values to produce the CO
2
concentration which is then normalized for changes in sample pressure.
10.1.4. Interference and Signal to Noise Rejection
If an interfering gas, such as H
2
O vapor is introduced into the sample chamber, the spectrum of the IR beam is
changed in a way that is identical for both the reference and the measurement cells, but without changing the
ratio between the peak heights of CO2 MEAS and CO2 REF. In effect, the difference between the peak heights
remains the same.
IR shining through both cells is effected
equally by interfering gas in the Sample
Chamber
M/R
is Shifted
Figure 10-5: Effects of Interfering Gas on CO2 MEAS & CO2 REF
166 05232 Rev B3