TP01Thermal properties sensor
| sensor specifications: | |
| Temperature range | -30 to +80 °C |
| Sensor thickness (nominal) | 0.15 mm |
| Required readout | 2 diff voltage channels 1V, 5 mV range |
| Voltage input (nominal) | 1-2 VDC |
| Typical heating cycle duration | ± 3 min at 0.05 W |
| Range λ | 0.3 to 4 W/m.K |
| Measurement accuracy λ | ± 5% |
| Measurement accuracy a | ± 20% |
| Measurement accuracy Cv | λ / a |
| Measurement resolution Cv | 10% |
| Heating power / m (nominal) | 0.8 W/m |
Figure 1 above: TP01 sensor: thermopiles (1), heating wire (2), cable (3). Dimensions in mm.
below: graphs in different soil types: signal amplitude varies with 1/ ?, signal response time varies with a. All dimensions are in mm.
The TP01 is a sensor for the long-term monitoring of soil thermal conductivity, thermal diffusivity and heat capacity.
A nice clear print of the original product brochure.
TP01 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 TP01 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 TP01; 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.
Suggested Use
- Scientific study of the heat storage as part of the surface energy balance
- Redundancy for soil moisture content