Campbell Scientific IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer - Manual (Page 41)

IRGASON ® Integrated CO
2
/H
2
O Open-Path Gas Analyzer and 3D Sonic Anemometer
Use mixtures of CO
2
and ambient air for the CO
2
span gas. The
use of reference CO
2
gas mixtures in pure nitrogen will lead to
errors due to a carrier gas effect on pressure-broadening of the CO
2
absorption lines since oxygen gas has a smaller line-broadening
coefficient than nitrogen.
FIGURE 9-5. ECMon zero-and-span window
9. Remove the CO
2
span gas from the inlet of the shroud, and replace it with
H
2
O span gas from a dew-point generator or another standard reference.
Because water molecules can adsorb to inside of the tubing and the shroud,
it may take many minutes for the H
2
O concentration to stabilize. If
desired, increase the flow rate for the first several minutes to more quickly
stabilize the system before returning it to between 0.4 and 0.6 l/min to
make the H
2
O measurement. Write down the reported H
2
O concentration.
10. Remove the H
2
O span gas, and connect a zero air source (no CO
2
or H
2
O)
to the inlet tube of the shroud. As described in step 8, use a pressure
regulator and flow controller so that zero air flows through the shroud
between 0.4 and 0.6 l/min. Wait for the measurement readings to stabilize
(this may require several minutes) and write down the reported values for
CO
2
and H
2
O concentrations. If the readings remain erratic, ensure that
flow of the zero air is sufficient and the shroud is correctly seated on the
snouts.
NOTE
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