LI-COR LI-6400, Manual

Page: 74 / 846

Guided Tours
Tour #3: Controlling Chamber Conditions
3-22 Using the LI-6400
3
4 Note the reference and sample water vapor channels
If itÕs not already there, put display line a on the top line. The two variables
on the right ( H2OR_mml and H2OS_mml ) are reference and sample water
mole fractions, in mmol mol
-1
. The reference should be near zero, since we
are forcing all the air through the desiccant. The sample may be near 15
mmol mol
-1
, but it depends on how wet your ÒleafÓ is, what the temperature
is, etc.
5 Note the flow rate and relative humidity
Put display line b on the second line. The third item in that line is the flow rate
( Flow_µml ). The displayed value should match (usually within 1 µmol s
-1
)
the target value shown on the flow control function key label ( f2 level 2). The
fourth item ( RH_S_% ) is relative humidity in the sample cell, in percent.
6 Change the desiccant to full bypass
Observe what happens when you change the desiccant from full scrub to full
bypass. The reference (
H2OR_mml ) will increase to whatever the ambient
humidity is, since we are now not drying the incoming airstream at all. The
N) None (Pump OFF)
Humidity Control Options & Targets
F)
¨
Flow Rate (500 µmol/s)
H) H2O_sample 20.0 mmol
R) RH_sample 50%
V) VPD ( Tleaf¡C) 1.00 kPa
Figure 3-17. Pressing f2 brings up the humidity control panel (part a). Press F to select fixed flow rate,
then enter the target value (part b).
500 µmol/s #
Flow rate
a)
b)
Highlight the desired
control option, and
press
enter . Or just
type the letter.
The prompt for the target
indicates the default val-
ue. (WhatÕs the # for?
See
Variable Targets
on page 7-5)
399.7 365.9 0.143 15.13
CO2R_µml CO2S_µml H2OR_mml H2OS_mml
a
-33.8 14.91 700.8 52.01
ÆCO2_µml ÆH2O_mml Flow_µml RH_S %
b