Campbell Scientific CR10X Measurement and Control System - Manual (Page 262)

APPENDIX F. DYNAGAGE SAP-FLOW (P67)
F-2
and 8 are 0.5 °C and 0.042 cm s
-1
, respectively.
These values should be used unless conditions
determined by the user indicate 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 -0.036 g 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.
PARAMETER 8
High Flow Filter (0.042 cm s
-1
). This filter sets F
equal to a calculated theoretical maximum flow
(F
max
) if F is greater than F
max
. F
max
equals the
theoretical maximum velocity (V
max
) multiplied
by the cross sectional area of the stem
(F
max
= V
max
∗ A).
This filter is used to protect the integrity of the
flow accumulator when the gage capacity to
measure F has been exceeded. When F is
exceptionally high, nearly all of the heat is
absorbed by the sap. As F continues to
increase, dT approaches zero asymptotically.
As dT becomes infinitesimal, previously
insignificant thermal noise from radiation or
other sources can cause a major exaggeration
of F. The value 0.042 cm s
-1
for V
max
was
determined by Dynamax to be a typical
maximum. At the users option, V
max
(Parameter
8) can be increased or decreased when the
species under study is verified to be accurately
measured.
F2.4 INSTRUCTION OUTPUT
PARAMETER 9
Two output options are available.
Option 0 Option 1
Sapflow (g h
-1
) Sapflow (g h
-1
)
K
shapp
(W mV
-1
) K
shapp
(W mV
-1
)
dT (°C)
power input (W)
Q
v
(Vertical Flux, W)
Q
r
(Radial Flux, W)
Q
f
(Sapflow Flux, W)
F2.4.1 Sapflow (g h
-1
)
The calculated sap flow rate. If total sapflow is
desired, Output Processing Instruction 72 can
be used in conjunction with Instruction 67 to
totalize sap flow.
F2.4.2 Qf and dT
Q
f
is the residual energy that is assumed lost
through sap flow and is defined as:
Q
f
= Q
h
- (Q
r
+ Q
v
)
The temperature difference, dT, is defined as:
dT = Upper TC - Lower TC
where the Upper TC is the thermocouple above
the heater and the Lower TC is the
thermocouple below the heater.
F2.4.3 Q
r
, K
sh
, K
shapp
Qr, radial energy loss, is the loss of energy
through the cork and foam sheath on the
sensor. K
sh
, the thermal conductivity constant,
is used to calculate Q
r
. Since Q
r
can be a large
percentage of the total energy loss, K
sh
must be
determined accurately as outlined in the
Dynagage manual. The essence of the
procedure is to record K
sh
(the second output of
Instruction 67, K
shapp
) when there is no stem
flow such as at dawn. This value is then placed
in Instruction 67, Parameter 2, K
sh
(W mV
-1
).
K
shapp
and K
sh
(W mV
-1
) have no effect on each
other in Instruction 67. K
sh
must be determined
for each installation.
F2.4.4 Power Input (W)
Power input or Q
h
is calculated from the input
voltage and heater resistance: Q
h
= V/R.
F2.4.5 Qv (W)
Qv, or vertical energy loss, is the loss of energy
through the wood at the ends of the sensor not
associated with the heating of the sap.