Campbell HFT3 Manuel utilisateur

INSTRUCTION MANUAL

HFT3 Soil Heat Flux Plate

Revision: 10/03

Campbell Scientific, Inc.

Warranty and Assistance

The HFT3 SOIL HEAT FLUX PLATE is warranted by CAMPBELL

SCIENTIFIC, INC. to be free from defects in materials and workmanship under

normal use and service for twelve (12) months from date of shipment unless

specified otherwise. Batteries have no warranty. CAMPBELL SCIENTIFIC,

INC.'s obligation under this warranty is limited to repairing or replacing (at

CAMPBELL SCIENTIFIC, INC.'s option) defective products. The customer

shall assume all costs of removing, reinstalling, and shipping defective products

to CAMPBELL SCIENTIFIC, INC. CAMPBELL SCIENTIFIC, INC. will

return such products by surface carrier prepaid. This warranty shall not apply

to any CAMPBELL SCIENTIFIC, INC. products which have been subjected to

modification, misuse, neglect, accidents of nature, or shipping damage. This

warranty is in lieu of all other warranties, expressed or implied, including

warranties of merchantability or fitness for a particular purpose. CAMPBELL

SCIENTIFIC, INC. is not liable for special, indirect, incidental, or

consequential damages.

Products may not be returned without prior authorization. The following

contact information is for US and International customers residing in countries

served by Campbell Scientific, Inc. directly. Affiliate companies handle repairs

for customers within their territories. Please visit www.campbellsci.com to

determine which Campbell Scientific company serves your country. To obtain

a Returned Materials Authorization (RMA), contact CAMPBELL

SCIENTIFIC, INC., phone (435) 753-2342. After an applications engineer

determines the nature of the problem, an RMA number will be issued. Please

write this number clearly on the outside of the shipping container.

CAMPBELL SCIENTIFIC's shipping address is:

CAMPBELL SCIENTIFIC, INC.

RMA#_____

815 West 1800 North

Logan, Utah 84321-1784

CAMPBELL SCIENTIFIC, INC. does not accept collect calls.

HFT3 Table of Contents

PDF viewers note: These page numbers refer to the printed version of this document. Use

the Adobe Acrobat® bookmarks tab for links to specific sections.

1. General Description....................................................1

2. Specifications .............................................................1

3. Installation...................................................................2

4. Wiring ..........................................................................3

5. Example Programs .....................................................4

6. Soil Heat Flux and Storage.........................................5

7. Maintenance................................................................6

8. References ..................................................................6

Figures

1. Placement of Heat Flux Plates ....................................................................2

2. HFT3 Plate to Datalogger Connections......................................................3

Tables

1. Datalogger Connections for a Single-Ended Measurement.........................3

2. Datalogger Connections for a Differential Measurement............................3

3. Wiring for Example 1 .................................................................................4

4. Wiring for Example 2 .................................................................................4

This is a blank page.

Model HFT3 Soil Heat Flux Plate

1. General Description

The HFT3 Soil Heat Flux plate uses a thermopile to measure temperature

gradients across the plate. Each plate is individually calibrated to output flux.

In order to measure soil heat flux at the surface, several HFT3s are used to

measure the soil heat flux at a depth of eight cm. A TCAV Averaging Soil

Thermocouple is used to measure the temporal change in temperature of the

soil layer above the HFT3. Finally, a CS615 Water Content Reflectometer is

used to measure the soil water content. The temporal change in soil

temperature and soil water content are used to compute the soil storage term.

The -L option on the model HFT3 Soil Heat Flux plate (HFT3-L) indicates that

the cable length is user specified. This manual refers to the sensor as the

HFT3.

2. Specifications

Operating Temperature: -40°C to +55°C

Storage Temperature: -40°C to +55°C

Plate Thickness: 3.91 mm (0.154 in.)

Plate Diameter: 38.2 mm (1.5 in.)

Sensor: thermopile

Measurement Range: ±100 W m-2

Signal Range: ±2.4 mV for the above range

Accuracy: better than ±5% of reading

Thermal Conductivity: 1.22 W m-1 K-1

Model HFT3 Soil Heat Flux Plate

2 cm

6 cm

8 cm

Ground Surface

Up to 1 m

2.5 cm

FIGURE 1. Placement of Heat Flux Plates

3. Installation

The HFT3 Soil Heat Flux plates, the TCAV Averaging Soil Temperature

probes, and the CS615 Water Content Reflectometer are installed as shown in

Figure 1.

The location of the heat flux plates and thermocouples should be chosen to be

representative of the area under study. If the ground cover is extremely varied,

it may be necessary to have additional sensors to provide a valid average of soil

heat flux.

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 eight cm below the surface into the undisturbed face of the hole. Insert the

heat flux plate into the horizontal cut.

Install the HFT3 in the soil such that the side with the white dot is

facing the sky.

In order for the HFT3 to make quality soil heat flux

measurements, the plate must be in full contact with the

soil.

NOTE

CAUTION

Partial emplacement of the HFT3 and the TCAV

sensors is shown for illustration purposes. All

sensors must be completely inserted into the soil face

before the hole is backfilled.

Model HFT3 Soil Heat Flux Plate

Never run the sensors leads directly to the surface. Rather, bury the sensor

leads a short distance back from the hole to minimize thermal conduction on

the lead wire. Replace the excavated soil back into it original position after all

the sensors are installed.

FIGURE 2. HFT3 Plate to Datalogger Connections

TABLE 1. Datalogger Connections for a Single-Ended Measurement

Description Color CR10(X), CR510 CR23X, 21X, CR7

Signal Black Single-Ended Input Single-Ended Input

Signal Reference White AG

Shield Clear G

TABLE 2. Datalogger Connections for a Differential Measurement

Description Color CR10(X), CR510 CR23X, 21X, CR7

Signal Black Differential Input (H) Differential Input (H)

Signal Reference White Differential Input (L) Differential Input (L)

Shield Clear G

4. Wiring

Connections to Campbell Scientific dataloggers are given in Tables 1 and 2.

The output of the HFT3 can be measured using a single-ended analog

measurement (Instruction 1) or a differential analog measurement (Instruction

2).

Signal Black

Signal Reference White

Shield Clear

White Dot

on Top

Model HFT3 Soil Heat Flux Plate

The wiring convention is that the black wire is positive with respect to the other

insulated wire, when energy is flowing through the transducer from the side

with white dot to the side without the white dot.

5. Example Programs

This section is for users who write their own dataloger programs. A datalogger

program to measure the sensor can be created using Campbell Scientific’s Short

Cut Program Builder software. You do not need to read this section if you use

Short Cut.

The HFT3 has a nominal calibration of 42 W m-2 mV-1. Each sensor is

accompanied with a calibration certificate. Each sensor has a unique

calibration label on it. The label is located on the pigtail end of the sensor

leads.

TABLE 3. Wiring for Example 1

Description Color CR10(X)

Signal Black SE 5 (3H)

Signal Reference White AG

Shield Clear G

Example 1 Sample CR10(X) Program using a Single-Ended Measurement Instruction

01: Volt (SE) (P1)

1: 1 Reps

2: 2 7.5 mV Slow Range ;CR510 (7.5 mV);CR23X (10 mV); 21X, CR7 (5 mV)

3: 5 SE Channel ;Black wire (SE 5), White wire (AG)

4: 1 Loc [ HFT3 ]

5: 1 Mult ;Enter Calibration

6: 0 Offset

TABLE 4. Wiring for Example 2

Description Color CR23X

Signal Black 9H

Signal Reference White 9L

Shield Clear

Model HFT3 Soil Heat Flux Plate

Example 2 Sample CR23X Program using a Differential Measurement Instruction

;Measure the HFT3 Soil Heat Flux plate.

;

01: Volt (Diff) (P2)

1: 1 Reps

2: 21 10 mV, 60 Hz Reject, Slow Range ;CR510, CR10(X) (7.5 mV); 21X, CR7 (5 mV)

3: 9 DIFF Channel ;Black wire (9H); White wire (9L)

4: 1 Loc [ HFT3 ]

5: 1 Mult ;Enter Calibration

6: 0 Offset

6. Soil Heat Flux and Storage

The soil heat flux at the surface is calculated by adding the measured flux at a

fixed depth, d, to the energy stored in the layer above the heat flux plates. The

specific heat of the soil and the change in soil temperature, ∆Ts, over the output

interval, t, are required to calculate the stored energy.

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. The heat capacity of the moist soil is given by:

(

)

CCCC C

sbdmw bdvww

=+ =+ρθ ρθρ (1)

θρ

ρθ

=(2)

where CSis the heat capacity of moist soil, ρbis bulk density, ρwis the density

of water, Cdis the heat capacity of a dry mineral soil, θmis soil water content

on a mass basis, θvis soil water content on a volume basis, and Cwis the heat

capacity of water.

This calculation requires site specific inputs for bulk density, mass basis soil

water content or volume basis soil water content, and the specific heat of the

dry soil. Bulk density and mass basis soil water content can be found by

sampling (Klute, 1986). The volumetric soil water content is measured by the

CS615 water content reflectometer. A value of 840 J kg-1 K-1 for the heat

capacity of dry soil is a reasonable value for most mineral soils (Hanks and

Ashcroft, 1980).

The storage term is then given by Eq. (3) and the soil heat flux at the surface is

given by Eq. (4).

STCd

∆

(3)

GG S

sfc cm

8(4)

Model HFT3 Soil Heat Flux Plate

7. Maintenance

The HFT3 requires minimal maintenance. Check the sensor leads monthly for

rodent damage.

Recalibrate the HFT3 every two years of continuous use. Obtain an RMA

number before returning the HFT3 to Campbell Scientific for calibration.

8. References

Hanks, R. J., and G. L. Ashcroft, 1980: Applied Soil Physics: Soil Water and

Temperature Application. Springer-Verlag, 159 pp.

Klute, A., 1986: Method of Soil Analysis. No. 9, Part 1, Sections 13 and 21,

American Society of Agronomy, Inc., Soil Science Society of America,

Inc.

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