Installing Self-calibrating Soil Heat Flux Plates in Biomet Systems

Printable PDF: Installing Self-calibrating Soil Heat Flux Plates in Biomet Systems

(Installing-SC-SHF-Plates-17841.pdf))

Download this content as a pdf that can be saved to your computer or printed.

Hukseflux HFP01SC self-calibrating soil heat flux plates (part number 7900-155) measure heat exchange across the plane of the plate. Here we provide basic installation and operation guidelines for the HFP01SC in LI-COR biomet data acquisition systems. Be sure to read the manufacturer's instructions before using the HFP01 Soil Heat Flux Plates.

HFP01SC Specifications:
Nominal sensitivity: 67 μv/W/m2
Typical range: -100 to 300 W/m2
Nominal sensor resistance: 2 ohm
Nominal heater resistance: 100 ohm
Operating temperature: -30 to +70 °C
Power consumption (during calibration): 1.3 W (108 mA @12 VDC)
Measurement range: ±2000 W/m2
Expected accuracy: ±3%
Thermal conductivity: 0.8 W/mK
Sensor signal range: ±5 mV for the above range
Heater signal range: 0 to 2 V (while powered)
Cable lengths: 15 meters

Siting soil heat flux plates

In a typical installation, three or more heat flux plates are needed in order to ensure good representation of the site.

Soil heat flux plates should be installed in the vicinity of the eddy covariance tower.

Place each heat flux plate in a shallow pit in soil that is representative of the site. More sensors may be needed if the soil is highly variable. Heat flux plates, soil moisture sensors, and soil temperature sensors can be placed in the same excavation.

Burying the heat flux plates

Excavate a small hole with a smooth, undisturbed side. Keep the excavated soil as an intact block if possible. Make a horizontal slit in the smooth side of the excavation 5 cm below the soil surface.

With the red side facing up toward the sky, gently insert the heat flux plate in the slit until it is completely covered by soil. Be sure the plate is in full contact with the soil and that there are no air pockets around it. Bury a length of the sensor leads to prevent thermal conduction through the wires. Fill the hole with the excavated soil.

Wiring self-calibrating soil heat flux plates

The bare leads connect directly to the DAqM. Wire assignments are given in Table 1‑1.

Table 1‑1. Wiring connections for self-calibrating soil heat flux plate data cables.
Data wires Connections
Description Color Plate 1 Plate 2 Plate 3
Signal (+) White A1 A3 A5
Signal (-) Green A2 A4 A6
Shield Black G1 G2 G3
Heater wires Connections
Description Color Plate 1 Plate 2 Plate 3
Power Brown SW1 SW2 SW3
Ground Black GND GND GND
Signal Green GND GND GND

Configuring self-calibrating soil heat flux plates

Each self-calibrating soil heat flux plate includes a unique sensitivity constant (Sreference on the calibration sheet). It is printed on the sensor cable label in units of µV/(W/m2). The calibration constants should be entered directly into the datalogger software for the variable SHF_SENS_#..

Each plate has a unique heater resistance constant (Rheater). The heater resistance of each plate should be entered for the variable R_SELF_#. Enter these values for each self-calibrating soil heat flux plate.

Select a program (Biomet Library) and then enter the calibration multipliers.

Save the configuration and push the file to the data acquisition system after entering the remaining calibration information.

Retrieving data

The SmartFlux System will log these data in compressed files for processing by EddyPro Software and evaluation by Tovi Software. Data are stored on the USB drive on the SmartFlux System. Refer to the Data Acquisition System instruction manual for details.

Maintenance

Check the data for plausible values. Periodically check the cables for rodent damage. Recalibrate the sensors every two years according to the manufacturer's instructions.