LI-COR LI-6400, Manual

Page: 469 / 846

Calibration Issues
CO2 and H2O Analyzers
Using the LI-6400 18-13
Setting the H
2
O Span
To check the span of the H
2
O analyzer, youÕll need a known concentration of
H
2
O. The best choice for this is the LI-COR Dew Point Generator (LI-610).
The H
2
O IRGA gain adjustment is a process by which the user can manually
(using the arrow keys
-¯
) adjust the values of G
wr
and G
ws
(see Equations
(14-5) and (14-6) on page 14-5).
■ ■ ■ ■
To set the H
2
O Span
1 Setup the LI-610 for an appropriate dew point
Subtract about 5C from room temperature, and use that for the target dew
point temperature. Wait until the condensorÕs temperature (as monitored on
the LI-610) reaches this target.
The reason for this 5C ÒbufferÓ is to avoid condensation in the line between
the LI-610Õs condensor and the IRGA. If condensation happens, you will
have large errors.
2 Set the flow rate.
Use about a 0.5 l min
-1
flow from the LI-610.
3 Attach to the IRGA
You have the same choice, as shown in Figure 18-6 on page 18-12. Here,
however, we would recommend option B: splitting the flow and connecting
both the reference and sample, with Match Off. The reason for this is that you
will be able to drastically reduce the equilibrium time, waiting for the sample
cell, as you will see.
4 View water channels
Press F3 or F4 to make the water IRGAs the active ones.
5 Wait for equilibrium
If you are using Option A (connected to sample, Match On), then be prepared
to wait about 20 minutes, until the rise in sample and reference concentration
is negligible.
If you are plumbed for Option B (sample and reference connected), ignore the
If you do not have an LI-610, or some device of similar
accuracy, do
not adjust the IRGA span values for water.