Model HFP01 Soil Heat Flux Plate Revision: 7/12 C o p y r i g h t © 2 0 0 2 - 2 0 1 2 C a m p b e l l S c i e n t i f i c , I n c .
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HFP01 Table of Contents PDF viewers: These page numbers refer to the printed version of this document. Use the PDF reader bookmarks tab for links to specific sections. 1. Introduction..................................................................1 2. Cautionary Statements................................................1 3. Initial Inspection ..........................................................1 4. Overview.......................................................................1 5. Specifications ..
Model HFP01 Soil Heat Flux Plate 1. Introduction The HFP01 outputs a voltage signal that is proportional to the heat flux of the surrounding medium (usually soil). It is typically used for energy-balance or Bowen-ratio flux systems. At least two sensors are required for each site to provide spatial averaging. Sites with heterogeneous media may require additional sensors.
Model HFP01 Soil Heat Flux Plate 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.
Model HFP01 Soil Heat Flux Plate Weight (w/o cable): 200 g (7.05 oz) Sensor: Thermopile Measurement Range: ±2000 W m-2 Sensitivity (nominal): 50 μV W-1 m-2 Expected Typical Accuracy (12 hour totals): within -15% to +5% in most common soils Nominal Resistance: 2W Sensor Thermal Resistance: <6.25 x 10-3 Km2W-1 Up to 1 m 2.5 cm 2 cm Ground 6 cm Surfac e 8 cm Partial emplacement of the HFP01 and the TCAV sensors is shown for illustration purposes.
Model HFP01 Soil Heat Flux Plate Use a small shovel to make a vertical slice in the soil. Excavate the soil to one side of the slice. Keep this soil intact so that is can be replaced with minimal disruption. The sensors are installed in the undisturbed face of the hole. Measure the sensor depths from the top of the hole. With a small knife, make a horizontal cut 8 cm below the surface into the undisturbed face of the hole. Insert the heat flux plate into the horizontal cut.
Model HFP01 Soil Heat Flux Plate 6.2 Wiring Connections to Campbell Scientific dataloggers are given in Table 6-1 and Figure 6-2. The output of the HF01 can be measured using a single-ended analog measurement (VoltSE() in CRBasic or Instruction 1 in Edlog) or a differential analog measurement (VoltDiff() in CRBasic or Instruction 2 in Edlog). TABLE 6-1.
Model HFP01 Soil Heat Flux Plate Example 1. Sample CR3000 Program using Differential Measurement Instructions 'CR3000 Series Datalogger 'Copyright (c) 2007, Campbell Scientific, Inc. All rights reserved.
Model HFP01 Soil Heat Flux Plate Example 2. Portion of CR10(X) Program using the Single-Ended Measurement Instruction NOTE 01: Volt (SE) (P1) 1: 1 2: 2 3: 5 4: 1 5: 14.90 6: 0 The instruction below does not store data in final storage. P92, P77, and an output processing instruction are required to store the data permanently. Reps 7.5 mV Slow Range SE Channel Loc [ HFP01 ] Mult Offset ;CR510 (7.5 mV);CR23X (10 mV); 21X, CR7 (5 mV) ;White wire (SE 5), Green wire (AG) ;Enter Calibration TABLE 6-4.
Model HFP01 Soil Heat Flux Plate The heat capacity of the soil is calculated by adding the specific heat of the dry soil to that of the soil water. The values used for specific heat of dry soil and water are on a mass basis.
Appendix A. General Theory of Heat Flux Sensors This Appendix discusses the general theory and characteristics of heat flux sensors similar to the HFP01. A.1 General Theory constantan filler FIGURE A-1. General characteristics of a heat flux sensor When heat is flowing through the sensor in the indicated direction, the filling material will act as a thermal resistance. Consequently the heat flow, ϕ, will follow a temperature gradient across the sensor, flowing from the hot to the cold side.
Appendix A. General Theory of Heat Flux Sensors better if the soil conditions are closer to the reference conditions (see the sensor specifications) and, in an actual experiment, the expected error range will probably be ±10%. The reference conditions for the calibration are a thermal conductivity of 0.8 W/mK and a nominal temperature of 20°C. A.2 Extended Theory It is obvious that there is the possibility that the sensor itself can significantly disturb the phenomenon that it is supposed to measure.
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