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TP01 thermal properties sensor

Thermal properties sensor

TP01 is the leading sensor for long-term monitoring of soil thermal conductivity. A measurement with TP01 may also be used to estimate soil thermal diffusivity and volumic heat capacity, leading to a better understanding of dynamic (variable heat flux) thermal behaviour of soils. TP01 is designed for long-term use at one measurement location. Applied in meteorological surface flux measurement systems, TP01 improves the estimates of heat transport in the soil and of the so-called storage term.



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TP01 is the leading sensor for long-term monitoring of soil thermal conductivity.

TP01 measures soil thermal conductivity. It is designed for long-term on-site operation, buried in the soil. Its rated operating range is 0.3 to 4 W/(m∙K), which covers most inorganic soil types. The sensor inside TP01 is a temperature difference sensor consisting of 2 thermopiles. It measures the radial temperature difference around a heating wire with a record breaking sensitivity. Both the heating wire and the sensor are incorporated in a very thin plastic foil. It can be connected directly to commonly used data logging systems. The low thermal mass of TP01 also makes it suitable for measuring the thermal diffusivity.


Measurand thermal conductivity
Measurement range 0.3 to 5 W/(m•K)
Optional non-traceable measurands thermal diffusivity and volumic heat capacity
Optional trend monitoring soil water content
Rated operating environment surrounded by soil
Rated operating temperature range -30 to +80 °C
Sensor foil thickness 0.15 x 10⁻³ m
Interval between measurements 6 hr (typical), optionally 3 to 12 hr
Duration of measurement 360 s
Heating interval duration 180 s
Heater rated power supply 1 to 2 VDC, < 0.4 A
Power consumption daily average 0.007 W
Standard cable length 5 m
Measuring system requirements :
Required readout and control 2 x differential voltage, 1 x switchable power
Required uncertainty (k = 2) 10 x 10⁻⁶ V at 10⁻³ V, 5 x 10⁻³ V at 2 V
Order code TP01/cable length in m
  • longer cable, in multiples of 5 m, cable lengths above 20 m in multiples of 10 m


Suggested use

A typical TP01 is part of a meteorological surface flux measurement system in which also wind, humidity, soil heat flux, soil temperatures at different depths and net radiation are measured. TP01 then serves to improve the estimate of the so-called storage term, which is used to model thermal heat transport in the soil. Measurements with TP01 are often combined with soil temperature profile measurements with sensor model STP01 and measurements with heat flux sensor model HFP01SC. Soil thermal properties change as a function of depth, in particular close to the soil surface. A typical measurement location is equipped with sensors at several depths. For good spatial averaging at least 2 sensors (> 5 m apart) should be installed at every depth. Hukseflux has equipped several testbeds in the electrical power industry, to monitor dryout, thermal runaway and thermal stability around  mockup high-voltage power lines. Here the capability to perform a crude measurement of  thermal diffusivity is an important feature, for modelling behavior under dynamic loads.

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