LI-COR LI-7815, Instruction Manual

Page: 64 / 98

Section 6. Maintenance
Setting the CO₂ and H₂O zeroes
Select a quality zero gas that is free of volatile organic compounds (VOCs). The gas
should be 0 ppm CO
2
in air; the calibration will only be as good as the gas.
Caution: Do not use nitrogen-balanced gas. Use air-balanced gas for both the zero
and span. Do not power on the instrument with a 0 ppm CO
2
gas flowing
through the analyzer or the analyzer will not initialize properly.
1
Power on the instrument and let it warm up.
2 Plumb a gas to the air inlet as shown in Figure 6-1 on the previous page.
Set the pressure between ambient and 35 kPa (5 PSI) above ambient.
Observe the measurements on the home screen until they have stabilized. The slope
will be near zero.
3
Zero the analyzer.
Under
Options > Calibration
, click
Zero
. The software will indicate that a zero cal-
ibration has started and it will not report concentrations until the zero is set. This
usually takes about 5 minutes.
6-2 LI-7815 CO₂/H₂O Gas Analyzer