LI-COR LI-6400, Manual

Page: 124 / 846

Making Measurements
Preparation Check Lists
4-6 Using the LI-6400
4
then adjust it (see Zeroing the Leaf Temperature Thermocouple on page
18-19).
Finally, reconnect the thermocouple, open the chamber, and verify that
ÒTleaf_¡CÓ responds when the thermocouple warmed by touching it.
8 Set Desired Reference Values for CO
2
and H
2
O
If you are using the CO
2
mixer, set it to control on reference concentration
with a target of 400 µmol mol
-1
. Make sure that the soda lime is on full scrub.
If you are not using the CO
2
mixer, monitor the reference CO
2
concentration.
Is CO2R_uml sufficiently stable? (Over a 30 s period, it should change less
than 2 µmol mol
-1
.) If not, use a larger buffer volume.
For H
2
O, set the desiccant at mid-range (between scrub and bypass) for now.
9 Leaks?
Set the flow rate to 200 µmol s
-1
. With the chamber closed and empty, exhale
around the chamber gaskets, and look for any fluctuations in the sample cell
CO
2
concentration ( CO2S_µml , display group a ). If there are no leaks, the
CO2S_µml value should not increase by more than 1 µmol mol
-1
.
10 Match the IRGAs
Matching the IRGAs is easily accomplished whether the chamber is empty or
not, but itÕs good policy to do this once right before starting a measurement.
Refer to
Matching the Analyzers on page 4-34 for how to do this.
Verify that the match valve is in fact working. Figure 4-4 on page 4-35 shows
what to look for.
You are now ready to clamp onto a leaf and begin measurements.
Clamping Onto the First Leaf
Once youÕve got the system behaving well with no leaf in the chamber, you
are ready to start. The basic procedure is quite simple: set initial conditions in
the chamber, put a leaf in the chamber, and do a final adjustment if necessary
so that you have the conditions in the chamber that you want, then wait for
things to stabilize.
1 Light
If using the LED source, set the light to the desired value (ambient is a good
value to start with - it wonÕt be an abrupt change for the leaf). If you arenÕt