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THERMAL
PROPERTIES SENSOR
TP-01-ATX
Thermal properties sensor
The TP-01-ATX is a
sensor for the long-term measurement of thermal conductivity, thermal
diffusivity and heat capacity in soil.
TP-01-ATX is designed
for long term (permanent) installation in soils. It covers the the thermal
conductivity (λ) range of 0.3 to 4 W/m.K, which is sufficient for most anorganic
soil types. The core of TP-01-ATX is a differential temperature sensor (2
thermopiles) (1) measuring the radial differential temperature with record
breaking sensitivity. The sensor performs a temperature measurement around a
heating wire (2).
Both heating
wire and sensor are incorporated in a very thin plastic foil. The low thermal
mass makes it suitable for estimating thermal diffusivity (a). Dividing λ by the
thermal diffusivity, a, gives the volumetric heat capacity Cv, which
varies with water content. The thermopile signal minus the initial offset (U -
U0) when heating with power Q depends on λ and a of the
medium.
U -
U0 = ( Eλ Q / λ ) F( a t )
Eλ is
a calibration constant, t is time, F is a function that equals 1 for large at.
By looking at the steady state signal amplitude λ can be determined.
Cv and a can be found by looking at the 63% response time for F. The
detection of changes in Cv (and water content) is the strong point of
TP-01-ATX; the resolution is much better than the accuracy. The product manual can be
obtained via e-mail. A program for use
with the Campbell Scientific CR10X and CR1000 are available. Hukseflux has a
broad product range of sensors for thermal conductivity measurement; please
consult the product catalogue.
See also needle
type probes: TP02 and TP08
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Figure 1
above: TP-01-ATX sensor: thermopiles (1), heating wire (2), cable
(3). Dimensions in mm.
below: graphs
in different soil types: signal amplitude varies with 1/ λ, signal response time
varies with a. All dimensions are in mm. |
Suggested use
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Scientific
study of the heat storage as part of the surface energy balance
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Redundancy for
soil moisture content
Specifications
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Temperature range: -30 to +80
°C
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Sensor thickness (nominal):
0.15 mm
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Required readout: 2 diff
voltage channels 1 V , 5 mV range
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Voltage input (nominal): 1-2
VDC
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Typical heating cycle duration:
± 3 min at 0.05 W
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Range λ: 0.3 to 4
W/m.K
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Measurement accuracy λ: +/-
5%
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Measurement accuracy a: +/- 20
%
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Measurement accuracy
Cv: λ / a
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Measurement resolution
Cv: 10%
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Heating power / m (nominal):
0.8 W/m
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