LI-COR LI-7820, Instruction Manual

Page: 60 / 92

Section 6. Maintenance
Setting the N
2
O span and zero
Select quality zero and span gases that are balanced in air or manufactured air
(nitrogen and oxygen). The zero gas should be 0 ppb N
2
O. For the best span adjust-
ment, select a quality span gas with a N
2
O concentration near or slightly above the
concentrations you expect to measure. The calibrations will only be as good as the
gases.
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 N
2
O gas flowing
through the analyzer or the analyzer will not initialize properly.
1
Connect a tank of N
2
O in dry air or manufactured air to the air inlet ( Figure 6-1 on the previous
page).
The span gas will work for this.
2
Set the pressure between ambient and 35 kPa (5 PSI) above ambient.
3
Observe the measurements on the home screen until the N
2
O has stabilized.
The slope will be near zero.
4
Being careful to avoid introducing any H
2
O into the air, switch to the zero gas.
It is important that the air remain dry when changing from the span to the zero
gas.
5
Wait for the zero reading to stabilize, then set the N
2
O zero.
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-7820 N₂O/H₂O Gas Analyzer