Leaf Porometer Operator’s Manual
4. Sensor Head Calibration
36
conductance of 240 mmol m
-2
s
-1
. For the conductance
value of the calibration plate to be correct, a flat, moist sur-
face must be placed across the hole on the side marked "Fil-
ter Paper." This condition is achieved with a circular disk of
wet filter paper that is included in your calibration kit.
Additional filter disks may be purchased if you run out.
NOTE: Do not touch the calibration filter paper disk with your fin-
gers because oils in your skin will contaminate the disk and result in
improper readings. To aid in handling the filter paper disk and to
keep it clean, use the tweezers included in the calibration kit to hold
the calibration filter paper disk.
Wetting the filter paper
The wetness state of the filter paper is critical for an accu-
rate calibration. The paper must be wet enough to provide
a 100% humidity surface, but must not be too wet. If the
paper is too wet, free water will be pulled into the hole on
the calibration plate by surface tension and will change the
effective dimensions of the hole thereby changing the con-
ductance. The best method of ensuring the proper wetness
state is to use the "wet and flick" method. Use tweezers to
pick up the filter disk and then add one drop of the DI
water to the filter disk to saturate it. Then, while holding
the disk with the tweezers, give the filter paper a sharp flick
of the wrist or two to knock off any excess water. The
resulting paper should glisten, but there should be no drop
of excess water clinging to the disk. Please see the video of
proper Leaf Porometer calibration technique on the Deca-
gon website (www.decagon.com) for visual representation
of the dip and flick technique and the proper filter paper
wetness state.