Teledyne GFC-7001T - Trace CO Analyzer - Manual (Page 293)

Theory of Operation Teledyne API – Model T300/T300M CO Analyzer
Teledyne Analytical Instruments 293
IR unaffected by N
2
in Measurement Cell of
the GDC Wheel and no additional CO in the
Sample Chamber
IR affected by CO 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
in the Sample Chamber
IR shining through Reference Cell is
also reduced by additional CO in the
Sample Chamber, but to a lesser extent
M/R
is reduced
CO REF
CO MEAS
Figure 13-4: Affect of CO in the Sample on CO MEAS & CO REF
Once the GFC7001T/GFC7001TM 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
concentration which is then normalized for changes in sample pressure.
I NTERFERENCE AND S IGNAL TO N OISE R EJECTION
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 CO
MEAS and CO REF. In effect, the difference between the peak heights remains the
same.