Thermal Dissipation (Granier)
The Thermal Dissipation Probe (TDP) directly measures sap
velocity which can be converted to volumetric flow rate
given an accurate measurement of sapwood area for the
tree. TDP is an uncomplicated and inexpensive method
ideally suited to whole plant transpiration measurements
on large diameter trees. The principle of measurement was
developed by Dr. Andre Granier of INRA in France and has
been widely adopted by the plant science research
community since 1996.
The TDP is well suited to whole plant transpiration or water
use studies in applications such as forestry, horticulture and
viticulture. When measuring sap flow on trees or plants
under conditions of equal resource competition such as a
forest plantation, orchard or vineyard, a single sensor per
tree or vine may be adequate. For trees growing in mixed
species stands or native forests sap flow varies around the
circumference of the trees due to varying degrees of
competition for resources. Under these situations it is
advisable to measure the sap flow in each of the 4
quadrants of the tree and average these readings to
achieve a more accurate total sap flow.
Principle of measurement
The Thermal Dissipation technique measures the difference
in temperature (dT) between a heated upper needle and a
lower reference needle when placed in the sapwood, or
conducting xylem of a woody stem. Using a regulated,
known voltage, the stem is constantly heated to
approximately 8oC above ambient. As sap flows past the
two needles, the lower reference needle records the
ambient sap temperature and the upper heated needle is
cooled. If rapid sap flow occurs the difference in
temperature between the two needles is low as the heat
input from the upper needle is being quickly dissipated.
When sap flow is low or close to zero a maximum
difference in temperature or (dTmax) is recorded because
heat is no longer being dissipated from the heated upper
needle. Granier’s empirical equation then uses the
measured dT and dTmax values to calculate sap velocity.
Sensor design
The standard TDP-30 probe consists of two needles joined
together a fixed distance of 40mm apart. A copper and
constantan thermocouple is located in each needle at half
way distance or 15mm from the base of each needle. The
upper needle also contains a fixed line heater that is
constantly heated. The needles have a teflon coating
designed to aid in removal from stems and assist in reusing
the sensors for multiple installations.
Application
Enabling better global research outcomes in soil, plant & environmental monitoring.
www.ictinternational.com : [email protected] : +612 6772 6770
Thermal Dissipation (Granier)
Specifications
TDP-10
TDP-30
TDP-50
TDP-80
TDP-100
Length:
10mm (.4?)
30mm (1.2?)
50mm (2?)
80mm (3.2?)
100mm (3.4?)
Diameter:
1.2mm
1.2mm
1.65mm
1.65mm
1.65mm
T-Type T/C’s:
1 ea
1 ea
1 ea
2 ea
3 ea
Probe Spacing:
40mm
40mm
40mm
40mm
40mm
Power:
0.08 to 0.12 W
0.15 to 0.2 W
0.32 W
0.5 W
0.44 W
Cable:
10 ft, 5 core
10 ft, 5 core
10 ft, 5 core
10 ft, 6 core
10 ft, 7 core
Heater
Resistance:
26 Ohm
50 Ohm
78 Ohm
110 Ohm
145 Ohm
Operating Volts
2.0V @ ~8°C
3.0V @ ~8°C
5.0V @ ~8°C
7.5V @ ~8°C
8.0V @ ~8°C
Enabling better global research outcomes in soil, plant & environmental monitoring.
www.ictinternational.com : [email protected] : +612 6772 6770
Thermal Dissipation (Granier)
Accessories
Data to the Web
Wireless Communication Module - Includes; MCC Radio Frequency Logging Hub,
Comms and ICT Data View Software, GSM/2G/3G modem, 3V 5Ah Lithium
Polymer Battery, 11W solar panel, IP66 enclosure.
Wireless Communication
Wireless USB Radio communication device.
Wireless Data Collector
Wireless data logger. 4GB SD Card storage. Communicates with any ICT
International instrument.
Sap Flow Tool
Sap Flow Tool software for HFD and HRM. Single License. Unlimited access to
any number HRM or HFD datasets. Configured to analyse HRMx, CHPM, Tmax
data from the SFM Sap Flow Meter. Visualise PSY1, soil moisture, and
meteorological data.
Enabling better global research outcomes in soil, plant & environmental monitoring.
www.ictinternational.com : [email protected] : +612 6772 6770
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