LI-COR LI-600, Instruction Manual

Page: 92 / 131

Section 9. Theory of operation
9-5
Water vapor concentrations are dependent on the atmo-
spheric pressure and must be calculated in order to solve
the mass balance
9-9
where H
2
O
x
is the water vapor concentration in ref-
erence, sample cuvette and leaf (mmol H
2
O mol air
-1
)
VP
x
is the vapor pressure from equation 9-8 and Press is
atmospheric Pressure (kPa).
Boundary layer conductance
The portion of the leaf in the cuvette has the boundary
layer stripped by the air flow across the leaf surface. The
conductance of the boundary layer is measured using a
source of temperature-controlled water vapor where
total conductance = boundary layer conductance.
9-10 g
bw
= flow
2
× -6.755 E -5 + 0.0292302 × flow
where flow is the cuvette flow rate in (µmol s
-1
).
Implementation of equations in the LI-600
The equations implemented in the LI-600 are shown
below.
Sensor calculations
The following equations convert the sensor read-out in
volts to the appropriate units. The RH and flow sensor
equations currently take the following form to allow for
factory calibration and user-adjustable zero and span set-
tings:
9-11