LI-COR LI-6400, Manual

Page: 156 / 846

Making Measurements
Matching the Analyzers
4-38 Using the LI-6400
4
Ò CO2S Has Changed Ó
The sample cell CO
2
concentration at the start of match mode is retained, and
periodically compared to subsequent values as a stability check. Whenever
the difference exceeds 3.0 µmol mol
-1
, a warning appears (Figure 4-7).
Since the sample CO
2
concentration should not be affected by match mode,
drift in this value indicates a problem. The cause for such drift is either unsta-
ble incoming CO
2
, a leak, or a sudden change in photosynthetic rate. While
in match mode, if the sample CO
2
is stable but the reference varies, then there
is a leak in the chamber exhaust tube, or else a problem with the match valve
itself.See page 20-21 for troubleshooting help.
The best way to prevent this message is to not enter match mode when the
sample cell concentrations are unstable.
Ò Excessive Deltas Ó
If
MATCH
is pressed, and the difference between sample and reference IR-
GAs exceeds 10 µmol mol
-1
for CO
2
or 1 mmol mol
-1
for H
2
O, a warning
will be displayed:
IRGA Match Mode
ÒCONFIG.JoeÓ
CO2R_µml CO2S_µml H2OR_mml H2OS_mml
330.1 329.2 18.24 18.55
Prev: 00:22:01 CO2=402 H2O=18.6
exit
MATCH
CO2S has changed 4.5 ppm (leak?)
Message Line
IRGAs
Figure 4-7. The leak message appears if the CO2S_µml value is more than
3 µmol mol
-1
from the value it had when match mode was entered.
WARNING
Excessive Deltas!
-Chamber closed?
-Match valve working?
Still want to match?
Press (Y/N)