CR10X Reference Manual
F-2
These voltages are measured using Instruction 2. Voltages for locations 1-3 are
measured on the 2.5mV slow range. The voltage for location 4 is measured on the
2500mV slow range.
F.2.2 Constants
Parameters 2 to 6 are constants that must be entered for each Dynagage.
Parameter 2
K
sh
(W/mV), a constant required to relate the thermopile output proportionally to
the radial heat transfer.
Parameter 3
The heater resistance (Ohms), measured with an Ohm-meter.
Parameter 4
The cross-sectional area of the stem (sq cm).
Parameter 5
Thermal conductivity (W/m
∗
K). This number is generally 0.54W/m
∗
K for
herbaceous plants or 0.42W/m
∗
K for woody plants.
Parameter 6
Thermocouple gap (cm) is the distance between the thermocouples in the
Dynagage, measured in cm. This value is determined by Dynamax and is found in
the Dynagage documentation.
F.2.3 Filters
Two predictable conditions may occur when the output from the Dynagage is not
valid. These two conditions are very low flow rates and high flow rates, both of
which cause dT to approach zero. In these cases, the output must be filtered so
that only ‘reasonable’ flow rates are processed. To do this, values of 0.5°C and
0.042cms
-1
should be used for Parameters 7 and 8 respectively. You should use
these values unless your own site experience indicates otherwise.
Parameter 7
Low-flow filter (0.5°C). This filter sets the reported flow rate (F) to zero if Qf is
greater than or equal to 0 and less than 20% of Qh, and if dT is less than 0.5°C.
When there is a zero flow rate in a very small stem, dT approaches zero. In this
situation the flow rate (F) will be highly exaggerated if a minor residual Q
f
exists.
To avoid this, F is set to zero. Negative flow rates, resulting from negative dT
readings, are also filtered out. This may occur in small stems at night.
The reported flow rate is set to -0.036g h
-1
. This alerts the user to the possible need
of adjusting K
sh
. K
sh
may not be perfectly set, and it is possible that a large
negative flow will occur, which could adversely affect the flow accumulator. The
small negative number (-0.036) will not adversely affect the flow accumulator.