PP Systems CIRAS-2, Руководство оператора

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System Setup and Operation
CIRAS-2 Operator's Manual Version 2.04
- 52 -
4. Cuvette (An) Set mb (0-Dewpoint)
The An H
2
O is controlled to within 0.1 mb of the set value. Because of the good stirring in the cuvette, this
should be the concentration experienced by the leaf. Initially, the humidity will be set to 50% of ambient
and control will not commence for several minutes. This is because the software is determining 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.
5. Leaf to Cuvette VPD
Analysis H
2
O is controlled so that there is a constant Vapour Pressure Gradient (specified in mb) between
the leaf tissue (assumed to be saturated at leaf temperature) and the cuvette air. Initially, the humidity will
be set to 50% of ambient and control will not commence for several minutes. This is because the
software is determining the ambient humidity. Subsequently, changing the set 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.
About H
2
O Control Types
As with changes in CO
2
concentration, rapid changes in RH within the leaf chamber are wholly artificial
(from a physiological standpoint) and measurements should be suspended until stable conditions prevail.
Control Types 3, 4, 5 are dynamic, responding to feedback from the leaf. Leaf responses to changing
cuvette conditions may result in automatic adjustments to flow rate, which will require additional leaf
equilibration times.
Determination of Actual Ambient RH
Please note: Reference air is conditioned along its path to the leaf chamber by passing through soda
lime, which removes CO
2
, but adds water vapor to the gas stream. After next passing through the water
vapor equilibrator up to 10 mb of water vapor is removed, but RH in the air sample is still greater than
outside ambient RH.
To determine the actual ambient relative humidity
(in the leaf‟s undisturbed environment) you can simply
open the cuvette and observe the RH reading in the display. For a slightly faster and more accurate
reading temporarily remove the AN IN gas connection, allowing outside air to be directly drawn through the
Analysis side of the IRGAs. Temporarily remove the REF IN gas connection to see the corresponding
ambient water vapor value in mb Once you have determined and noted the true ambient RH (or water
vapor in mb) you can change your settings accordingly.
Remember to reconnect the gas connections
before proceeding.
PAR
Depending on cuvette type, enter a PAR Control Setpoint from 0-2,000 µmol m
2
s
-1
.
Cuvette Flow
Appears as above (see System Setup on page 49.)