System Setup and Operation
CIRAS-2 Operator's Manual Version 2.04
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Control Types
CO
2
(0
–2000 ppm)
Selections available from
the „CO
2
Control Types‟ dropdown list:
1. Supply (Ref) Approximate ppm
The actual Reference gas (gas stream entering the leaf chamber) control value achieved will be
approximately that of the entered value. CIRAS-2 should control CO
2
concentration to within
approximately 30 ppm of the value you enter in the „Control Setpoints‟ field (assuming fresh chemicals and
CO
2
source, proper gas connections, and good zeroing).
2. Supply (Ref) Set ppm
The Reference gas control value will be within 1 ppm of the set value.
3. Cuvette (An) Set ppm
The Analysis gas (gas stream exiting the leaf chamber) control value will be within 2 ppm of the set value.
About CO
2
Control Types
Control Types 1 and 2 are recommended for the most efficient control of CO
2
concentration, as neither is
influenced by the leaf response to chamber conditions. Control Type 1 allows rapid CO
2
concentration
changes and therefore faster overall leaf stabilization times, but the user must be aware to expect lower
precision in CO
2
control. Also, the absolute difference between the entered CO
2
value and the actual
Reference gas value can change with depleted chemicals and improperly conducted Zeroes. Control
Type 2 provides precise control. However, changing the CO
2
concentration using Control Type 2 results
in longer delays (up to several minutes) while the concentration stabilizes. In both cases measurements
should be suspended until the system is stable, as these data will be invalid.
H2O (0-100% or 0 mb-Dewpoint)
Selections available from the „H2O Control Types‟ dropdown list:
1. Supply (Ref) % Ambient
This H
2
O Control Type tracks humidity of the Reference air and allows you to mirror it precisely in the
cuvette, i.e. 0-100% of
ambient (Reference) humidity
. Using this you can set the leaf chamber humidity
level to some lower fraction of Reference air humidity. For example, say that there is 60% RH (or 14.0 mb
at 20 °C and standard pressure) in the Reference gas stream entering the leaf chamber. If you enter a
H2O Setpoint value of 50 (%) CIRAS-2 will rapidly dehumidify the gas stream entering the leaf chamber
such that RH in the chamber will be quickly lowered to 30% (or 7.0 mb).
2. Supply (Ref) Set mb
The Setpoint value is entered in mb (control range of 0-75 mb) and control of H
2
O partial pressure of the
Reference air should be within 0.1 mb. Lowering the mb value of the Reference air will rapidly dehumidify
the gas stream entering the leaf chamber such that RH in the chamber will decrease rapidly.
3. Cuvette (An) % RH (vs. Leaf T)
The Analysis air H
2
O is controlled to give the set % relative humidity in the cuvette with reference to leaf
temperature. Initially, the humidity will be set to 50% of ambient and control will not commence for several
minutes while the software determines the ambient humidity. Changing the set humidity value will result in
an immediate response as the software is continuously updating the value. However, changing the H
2
O
Control type may result in the same delay.
