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Soil Heat Flux Plate

The HFP01, manufactured by Hukseflux, measures soil heat flux, typically for energy-balance or Bowen-ratio flux systems. It outputs a voltage signal that is proportional to the heat flux of the surrounding medium. At least two sensors are required for each site to provide spatial averaging. Sites with heterogeneous media may require additional sensors.

Benefits and Features

  • Compatible with most Campbell Scientific dataloggers
  • Compatible with the CWS900-series interfaces, allowing it to be used in a wireless sensor network

Detailed Description

The HFP01 uses a thermopile to measure temperature gradients across its plate. Operating in a completely passive way, it generates a small output voltage that is proportional to this differential temperature. Assuming that the heat flux is steady, that the thermal conductivity of the body is constant, and that the sensor has negligible influence on the thermal flow pattern, the signal of the HFP01 is directly proportional to the local heat flux.

The HFP01’s output is in millivolts. To convert this measured voltage to heat flux, it must be divided by the plate’s calibration constant. A unique calibration constant is supplied with each sensor.

Note: In an energy-balance installation, all sensors must be completely inserted into the soil face before the hole is backfilled.


Sensor Type Thermopile
Sensitivity 50 μV W-1 m-2 (nominal)
Nominal Resistance 2 Ω
Temperature Range -30° to +70°C
Sensor Thermal Resistance < 6.25 x 10-3 K m2 W-1
Measurement Range ±2000 W m-2
Expected Typical Accuracy Within -15% to +5% in most common soils (12 hour totals)
Plate Diameter 80 mm (3.15 in.)
Plate Thickness 5 mm (0.20 in.)
Weight 200 g (7.05 oz) without cable