CIRAS-3 Operation Manual V. 1.09
199
Perform a Zero and Diff Bal cycle. Set up the graphical display to plot H2Od (H
2
O differential). Wait until
Tcuv is /- 0.5 C of Tamb.
With a syringe or moist cotton swab, carefully wet the exposed filter paper area. Avoid water on the
aluminum foil or plastic frame of the envelope. Do not wet the closed cell foam cuvette gasket - wetting
the gasket will increase the leaf chamber humidity and result in a failed test. Open the cuvette and place
the leaf stimulant envelope in the cuvette. Align the filter paper area of the envelope with the opening.
Close the cuvette and cover the leaf chamber with a dark cloth (PAR sensors read 0).
You should observe a rapid rise in the cuvette water vapor differential (H2Od) followed by a short stability
phase of perhaps 1 minute duration, depending on the degree of wetness of the filter paper. Note this
average H2Od value. As the paper dries due to evaporation the positive differential will fall back towards
Zero.
Open the RbCal.xls file available on the USB thumb drive (supplied by PP Systems when you first
purchased your system or visit our web site and download it) and enter the required values. For Air
Temperature, enter the cuvette temperature °C (Tcuv). Note that the evaporation rate (mmol m
-2
s
-1
) will
be much higher than typical leaf transpiration rates. Ensure that r
b
is ≤0.5 m
2
s mol
-1
. Typical results
range from 0.3-0.5. If not, rewet the filter paper (if dry) and rerun the test.
