Campbell HFP01SC Instruction Manual

MODEL HFP01SC

SELF-CALIBRATING SOIL HEAT FLUX PLATE

INSTRUCTION MANUAL

4/02

COPYRIGHT (c) 2002 CAMPBELL SCIENTIFIC, INC.

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Warranty and Assistance

The MODEL HFP01SC SELF-CALIBRATING 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. To obtain a
Returned Materials Authorization (RMA), contact CAMPBELL SCIENTIFIC,
INC., phone [phone]. 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.

Non-warranty products returned for repair should be accompanied by a
purchase order to cover the repair.

815 W. 1800 N.
Logan, UT 84321-1784
USA
Phone [phone]
FAX [phone]
www.campbellsci.com

Campbell Scientific Canada Corp.
11564 -149th Street
Edmonton, Alberta T5M 1W7
CANADA
Phone [phone]
FAX [phone]

Campbell Scientific Ltd.
Campbell Park
80 Hathern Road
Shepshed, Loughborough
LE12 9GX, U.K.
Phone [phone]
FAX [phone]

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HFP01SC Table of Contents

1. General Description

2. Sensor Specifications

3. Installation

4. Wiring

...................................................................2

..........................................................................4

5. Example Programs

....................................................1

................................................1

.....................................................4

6. Soil Heat Flux and Storage

7. Maintenance

..............................................................24

8. In-Situ Calibrati on Theor y

9. References

................................................................25

.......................................23

........................................24

Figures

Tables

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

2. HFP01SC Plate...........................................................................................3

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

2. Datalogger Connections for a Differential Measurement ...........................4

3. Wiring for Example 1.................................................................................5

4. Wiring for Example 2.................................................................................9

5. Wiring for Example 3...............................................................................14

6A. Wiring for Example 4............................................................................ 17

6B. Wiring for Example 4 ............................................................................17

7. Hukseflux and Campbell Scientific Variable Names................................24

i

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

1. General Description

The HFP01SC Soil Heat Flux plate consists of a thermopile and a film heater.
The thermopile measures temperature gradients across the plate. During the in­situ field cali bration, the film heater is used to generate a heat flux through the
plate. The amount of power used to generate the calibration heat flux is
measured by the datalogger. Each plate is individually calibrated, at the
factory, to output flux.

In order to measure soil heat flux at the surface, several HFP01SCs are used to
measure the soil heat flux at a depth of eight centimeters. A TCAV Averaging
Soil Thermocouple is used to measure the temporal change in temperature of
the soil layer above the HFP01SC. Finally, a CS616 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 HFP01SC Soil Heat Flux plate (HFP01SC-L)
indicates that the cable length is user specified. The HFP01SC-L has two
cables, the first cable is the signal output cable and the second is the heater
input cable. Two analog inputs are required to measure the HFP01SC-L This
manual refers to the sensor as the HFP01SC.

2. Specifications

Operating Temperature: -30°C to +70°C
Storage Temperature: -30°C to +70°C
Plate Thickness: 5 mm (0.2 in.)
Plate Diameter: 80 mm (3.15 in.)
Power Consumption
During Self Calibration: 1.3 W (108 mA @ 12 vdc)
Sensor: thermopile and film heater
Measurement Range: ±100 W m
Signal Range (nominal): ±5 mV for the above range (sensor), 0 to 2 V

(while the film heater is powered)

Accuracy: ±3% of reading
Sensitivity (nominal): 67 µV W
Sensor Resistance (nominal): 2 Ω
Heater Resistance (nominal): 100 Ω
Current Sensing Resistor: 10Ω 1% 0.25 W
Thermal Conductivity: 0.8 W m

-2

-1 m-2

-1 K-1

1

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

Up to 1 m

3. Installation

2.5 cm

6 cm

2 cm

Ground Surface

8 cm

Partial emplacement of the HFP01SC and the TCAV
sensors is shown for illustration purposes. All sensors
must be completely inserted into the soil face before
the hole is backfilled.

FIGURE 1. Placement of Heat Flux Plates

The HFP01SC Soil Heat Flux plates, the TCAV Averaging Soil Temperature
probes, and the CS616 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 spatial 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 kni fe, make a horizo nt al
cut eight centimeters below the surface into the undisturbed face of the hole.
Insert the heat flux plate into the horizontal cut.

NOTE

Install the HFP01SC in the soil such that the side with the text
“this side up” is facing the sky.

2

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

H

U

K

S

E

F

L

U

X

H

E

A

T

F

L

U

X

P

L

A

T

E

CAUTION

In order for the HFP01SC to make quality soil heat flux
measurements, the plate must be in full contact with the
soil.

Never run the sensors leads directly to the surface. Rather, bury the sensor
leads a short distance back from the hole to minimized thermal conduction on
the lead wire. Replace the excavated soil back into it original position after all
the sensors are installed.

Signal (White)

Signal Reference (Green)

Shield (Clear)

Heater Resistor Signal (Yellow)

Heater Resistor Signal Reference (Purple)

Shield (Clear)

Power (Red)

Power Reference (Black)

FIGURE 2. HFP01SC Plate

TABLE 1. Datalogger Connectio ns for a Single-Ended Measurement

Description Color CR10X CR23X & CR5000

Sensor Signal White Single-Ended Input Single-Ended Input

Sensor Signal Refere nce Green AG

Shield Clear G

Heater Resistor Signal Yellow Single-Ended Input Single-Ended Input
Heater Resistor Signal

Purple AG

Reference

Shield Clear G
Power Red SW12 SW12

Power Reference Black G G

External Power Control jumper wire SW12-CTRL to

Control Port

External Power

Control Not Needed

3

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

TABLE 2. Datalogger Connections for a Differential Measurement

Description Color CR10(X) CR23X & CR5000

Sensor Signal White Differential Input (H) Differential Input (H)

Sensor Signal Reference Green Differential Input (L) Differential Input (L)

Shield Clear G

Heater Resistor Signal Yello w Differential Input (H) Differential Input (H)
Heater Resistor Signal

Reference

Shield Clear G
Power Red SW12 SW12

Power Reference Black G G

External Power Control Jumper wire SW12-CTRL to

Purple Differential Input (L) Differential Input (L)

4. Wiring

Control Port

External Power

Control Not Needed

Connections to Campbell Scientific dataloggers are given in Tables 1 and 2.
The output of the HFP01SC can be measured using a single-ended analog
measurement (Instruction 1 or VoltSE()), however, a differential analog
measurement (Instruction 2 or VoltDiff()) is recommended.

The wiring convention is that the white wire is positive with respect to the
green wire, when energy is flo wing thr ough the transducer from the side with
the text “this side up” to the other side.

NOTE

The switched 12 vdc port on the black CR10X wiring panel can
source enough current to calibrate five HFP01SC plates; the
CR23X and CR5000 switched 12 vdc port can be used to
calibrate four HFP01SC plates. If additional HFP01SC plates
are needed an external relay is required to power the additional
plates (see example 4).

For dataloggers without a SW12V output (CR7X, 21X and CR10), a relay
(A21REL-12) is required for the in-situ calibration (see Example 4).

5. Example Programs

This section is for users who write their own datalogger 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 use Short Cut.

The HFP01SC has a nominal calibration of 15 W m
accompanied by a calibration certificate. Each sensor also has a unique
calibration label on it. The label is located on the pigtail end of the sensor
leads.

4

-2

mV-1. Each sensor is

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

TABLE 3. Wiring for Exa mple 1

Description Color CR10(X)

Sensor Signal White 1H

Sensor Signal Refere nce Green AG

Shield Clear G

Heater Resistor Signal Yellow 1L

Heater Resistor Signal Reference Purple AG

Shield Clear G
Power Red SW12

Power Reference Black G

External Power Control jumper wire SW12-CTRL to C8

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

;{CR10X}
;
*Table 1 Program

01: 1 Execution Interval (seconds)

;Measure HFP01SC on smaller range.
;
1: Volt (SE) (P1)

1: 1 Reps
2: 22 7.5 mV 60 Hz Rejection Range
3: 1 SE Channel
4: 2 Loc [ shf_mV ]
5: 1 Mult
6: 0 Offset

;Measure HFP01SC on larger range.
;
2: Volt (SE) (P1)

1: 1 Reps
2: 23 25 mV 60 Hz Rejection Range
3: 1 SE Channel
4: 8 Loc [ shf_mV_a ]
5: 1 Mult
6: 0 Offset

;Load in the factory calibration.
;
3: If (X<=>F) (P89)

1: 3 X Loc [ cal ]
2: 1 =
3: 0 F
4: 30 Then Do

5

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

;Factory calibration in W/(m^2 mV) = 1000/sensitivity.
;
4: Z=F (P30)

1: 1 F ; <- Enter the unique calibration here
2: 0 Exponent of 10

3: 3 Z Loc [ cal ]
5: End (P95)
;Use data from the larger measurement range.

;
6: If (X<=>F) (P89)

1: 2 X Loc [ shf_mV ]

2: 4 <

3: -99990 F

4: 30 Then Do
7: Z=X (P31)

1: 8 X Loc [ shf_mV_a ]

2: 2 Z Loc [ shf_mV ]
8: End (P95)
;Apply custom calibration to the raw soil heat flux measurement.

;
9: Z=X*Y (P36)

1: 2 X Loc [ shf_mV ]

2: 3 Y Loc [ cal ]

3: 1 Z Loc [ shf ]
;Output data.

;
10: If time is (P92)

1: 0 Minutes (Seconds --) into a

2: 20 Interval (same units as above)

3: 10 Set Outp ut Fl ag High (Flag 0)
11: Real Time (P77)

1: 0110 Day,Hour/Minute (midnight = 0000)
12: Resolution (P78)

1: 1 High Resolution
;Do not include the calibration data in the soil heat flux.

;
13: If Flag/Port (P91)

1: 18 Do if Flag 8 is High

2: 19 Set Intermed. Proc. Disable Flag High (Flag 9)
14: Average (P71)

1: 1 Reps

2: 1 Loc [ shf ]
15: Do (P86)

1: 29 Set Intermed. Proc. Disable Flag Low (Flag 9)

6

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

16: Sample (P70)

1: 1 Reps

2: 3 Loc [ cal ]
;Add other processing here.
;Call calibration routine.

;
17: Do (P86)

1: 8 Call Subroutine 8
*Table 2 Program

02: 0 Execution Interval (seconds)
*Table 3 Subroutines
;Calibration routine.

;
1: Beginning of Subroutine (P85)

1: 8 Subroutine 8
;Perform in-situ calibratation.

;
2: If time is (P92)

1: 1 Minutes (Seconds --) into a

2: 180 Interval (same units as above)

3: 30 Then Do
3: Z=X (P31)

1: 2 X Loc [ shf_mV ]

2: 4 Z Loc [ mV_0 ]
;Begin heating for calibration.

;
4: Do (P86)

1: 48 Set Port 8 High
;Used to filter data during and after calibration.

;
5: Do (P86)

1: 18 Set Flag 8 High
6: End (P95)
;End site calibration three minutes after calibration started.

;
7: If time is (P92)

1: 4 Minutes (Seconds --) into a

2: 180 Interval (same units as above)

3: 30 Then Do

7

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

;Measure volta ge across curre nt shunt resistor (10 ohm 1% 0.25 W 50
;ppm/deg C) during calibration. This measurement is used to
;compute power.
;
8: Volt (SE) (P1)

1: 1 Reps
2: 25 2500 mV 60 Hz Rejection Range
3: 2 SE Channel
4: 7 Loc [ V_Rf ]
5: .001 Mult
6: 0 Offset

9: Z=X (P31)

1: 2 X Loc [ shf_mV ]
2: 5 Z Loc [ mV_180 ]

;Turn off the soil heat flux plate heater.
;
10: Do (P86)

1: 58 Set Port 8 Low
11: End (P95)
;Stop filtering data.

;
12: If time is (P92)

1: 39 Minutes (Seconds --) into a

2: 180 Interval (same units as above)

3: 30 Then Do
13: Do (P86)

1: 28 Set Flag 8 Low
;Compute in-situ calibration.

;
14: Z=X (P31)

1: 2 X Loc [ shf_mV ]

2: 6 Z Loc [ mV_end ]
15: Z=X*Y (P36)

1: 7 X Loc [ V_Rf ]

2: 7 Y Loc [ V_Rf ]

3: 3 Z Loc [ cal ]
16: Z=X*F (P37)

1: 3 X Loc [ cal ]

2: 128.7 F

3: 3 Z Loc [ cal ]
17: Z=X+Y (P33)

1: 4 X Loc [ mV_0 ]

2: 6 Y Loc [ mV_end ]

3: 9 Z Loc [ work ]
18: Z=X*F (P37)

1: 9 X Loc [ work ]

2: .5 F

3: 9 Z Loc [ work ]

8

19: Z=X-Y (P35)

1: 9 X Loc [ work ]
2: 5 Y Loc [ mV_180 ]
3: 9 Z Loc [ work ]

20: Z=ABS(X) (P43)

1: 9 X Loc [ work ]
2: 9 Z Loc [ work ]

21: Z=X/Y (P38)

1: 3 X Loc [ cal ]
2: 9 Y Loc [ work ]

3: 3 Z Loc [ cal ]
22: End (P95)
23: End (P95)
End Program

-Input Locations­1 shf
2 shf_mV
3 cal
4 mV_0
5 mV_180
6 mV_end
7 V_Rf
8 shf_mV_a
9 work

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

TABLE 4. Wiring for Exa mple 2

Description Color CR23X

Sensor Signal White 9H

Sensor Signal Refere nce Green 9L

Shield Clear

Heater Resistor Signal Yellow 10H

Heater Resistor Signal Reference Purple 10L

Shield Clear
Power Red SW12

Power Reference Black G

9

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

Example 2. Sample CR23X Program Using a Differential Measurement Instruction

;{CR23X}
;
*Table 1 Program

01: 1 Execution Interval (seconds)

;Measure HFP01SC on smaller range.
;
1: Volt (Diff) (P2)

1: 1 Reps
2: 21 10 mV, 60 Hz Reject, Slow Range
3: 9 DIFF Channel
4: 2 Loc [ shf_mV ]
5: 1 Mult
6: 0 Offset

;Measure HFP01SC on larger range.
;
2: Volt (Diff) (P2)

1: 1 Reps
2: 25 5000 mV, 60 Hz Reject, Fast Range
3: 9 DIFF Channel
4: 8 Loc [ shf_mV_a ]
5: 1 Mult
6: 0 Offset

;Load in the factory calibration.
;
3: If (X<=>F) (P89)

1: 3 X Loc [ cal ]
2: 1 =
3: 0 F
4: 30 Then Do

;Factory calibration in W/(m^2 mV) = 1000/sensitivity.
;
4: Z=F (P30)

1: 1 F ; <- Enter the unique calibration here
2: 0 Exponent of 10

3: 3 Z Loc [ cal ]
5: End (P95)
;Use data from the larger measurement range.

;
6: If (X<=>F) (P89)

1: 2 X Loc [ shf_mV ]

2: 4 <

3: -99990 F

4: 30 Then Do
7: Z=X (P31)

1: 8 X Loc [ shf_mV_a ]

2: 2 Z Loc [ shf_mV ]

10

8: End (P95)

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

;Apply custom calibration to the raw soil heat flux measurement.
;
9: Z=X*Y (P36)

1: 2 X Loc [ shf_mV ]
2: 3 Y Loc [ cal ]
3: 1 Z Loc [ shf ]

;Output data.
;
10: If time is (P92)

1: 0 Minutes (Seconds --) into a
2: 20 Interval (same units as above)
3: 10 Set Outp ut Fl ag High (Flag 0)

11: Real Time (P77)

1: 0110 Day,Hour/Minute (midnight = 0000)

12: Resolution (P78)

1: 1 High Resolution

;Do not include that calibration data in the soil heat flux.
;
13: If Flag/Port (P91)

1: 18 Do if Flag 8 is High
2: 19 Set Intermed. Proc. Disable Flag High (Flag 9)

14: Average (P71)

1: 1 Reps
2: 1 Loc [ shf ]

15: Do (P86)

1: 29 Set Intermed. Proc. Disable Flag Low (Flag 9)

16: Sample (P70)

1: 1 Reps

2: 3 Loc [ cal ]
;Add other processing here.
;Call calibration routine.

;
17: Do (P86)

1: 8 Call Subroutine 8
*Table 2 Program

02: 0 Execution Interval (seconds)
*Table 3 Subroutines
;Calibration routine.

;
1: Beginning of Subroutine (P85)

1: 8 Subroutine 8
;Perform in-situ calibratation.

;

11

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

2: If time is (P92)

1: 1 Minutes (Seconds --) into a
2: 180 Interval (same units as above)
3: 30 Then Do

3: Z=X (P31)

1: 2 X Loc [ shf_mV ]
2: 4 Z Loc [ mV_0 ]

;Begin heating for calibration.
;
4: Do (P86)

1: 49 Turn On Switched 12V

;Used to filter data during and after calibration.
;
5: Do (P86)

1: 118 Set Flag 18 High
6: End (P95)
;End site calibration three minutes after calibration started.

;
7: If time is (P92)

1: 4 Minutes (Seconds --) into a

2: 180 Interval (same units as above)

3: 30 Then Do
;Measure voltage across curr ent shunt resistor d uring calibrati on.

;This measurement is used to compute power.
;
8: Volt (Diff) (P2)

1: 1 Reps

2: 25 5000 mV, 60 Hz Reject, Fast Range

3: 10 DIFF Channel

4: 7 Loc [ V_Rf ]

5: .001 Mult

6: 0 Offset
9: Z=X (P31)

1: 2 X Loc [ shf_mV ]

2: 5 Z Loc [ mV_180 ]
;Turn off the soil heat flux plate heater.

;
10: Do (P86)

1: 59 Turn Off Switched 12V
11: End (P95)
;Stop filtering data.

;
12: If time is (P92)

1: 39 Minutes (Seconds --) into a

2: 180 Interval (same units as above)

3: 30 Then Do

12

13: Do (P86)

1: 218 Set Flag 18 Low

;Compute in-situ clibration.
;
14: Z=X (P31)

1: 2 X Loc [ shf_mV ]
2: 6 Z Loc [ mV_end ]

15: Z=X*Y (P36)

1: 7 X Loc [ V_Rf ]
2: 7 Y Loc [ V_Rf ]
3: 3 Z Loc [ cal ]

16: Z=X*F (P37)

1: 3 X Loc [ cal ]
2: 128.7 F
3: 3 Z Loc [ cal ]

17: Z=X+Y (P33)

1: 4 X Loc [ mV_0 ]
2: 6 Y Loc [ mV_end ]
3: 9 Z Loc [ work ]

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

18: Z=X*F (P37)

1: 9 X Loc [ work ]
2: .5 F
3: 9 Z Loc [ work ]

19: Z=X-Y (P35)

1: 9 X Loc [ work ]
2: 5 Y Loc [ mV_180 ]
3: 9 Z Loc [ work ]

20: Z=ABS(X) (P43)

1: 9 X Loc [ work ]
2: 9 Z Loc [ work ]

21: Z=X/Y (P38)

1: 3 X Loc [ cal ]
2: 9 Y Loc [ work ]

3: 3 Z Loc [ cal ]
22: End (P95)
23: End (P95)
End Program

-Input Locations­1 shf
2 shf_mV
3 cal
4 mV_0
5 mV_180
6 mV_end
7 V_Rf
8 shf_mV_a
9 work

13

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

TABLE 5. Wiring for Exa mple 3

Description Color CR5000

Sensor Signal #1 White 11H

Sensor Signal Reference #1 Green 11L

Shield #1 Clear

Sensor Signal #2 White 12H

Sensor Signal Reference #2 Green 12L

Shield #2 Clear

Sensor Signal #3 White 13H

Sensor Signal Reference #3 Green 13L

Shield #3 Clear

Sensor Signal #4 White 14H

Sensor Signal Reference #4 Green 14L

Shield #4 Clear

Heater Resistor Signal #1 Yellow 17H

Heater Resistor Signal Reference #1 Purple 17L

Shield #1 Clear
Power #1 Red SW12

Power Reference #1 Black G

Heater Resistor Signal #2 Yellow 18H

Heater Resistor Signal Reference #2 Purple 18L

Shield #2 Clear
Power #2 Red SW12

Power Reference #2 Black G

Heater Resistor Signal #3 Yellow 19H

Heater Resistor Signal Reference #3 Purple 19L

Shield #3 Clear
Power #3 Red SW12

Power Reference #3 Black G

Heater Resistor Signal #4 Yellow 20H

Heater Resistor Signal Reference #4 Purple 20L

Shield #4 Clear
Power #4 Red SW12

14

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

Example 3. Sample CR5000 Program Using a Differential Measurement
Instruction

'CR5000

Const CAL_INTERVAL = 18 0 'HFP01SC calibration interval in minutes.

'*** Variables ***

Public shf(4)
Alias shf(1) = hfp01sc_1
Alias shf(2) = hfp01sc_2
Alias shf(3) = hfp01sc_3
Alias shf(4) = hfp01sc_4
Units shf = W/m^2

Public shf_cal(4)
Units shf_cal = W/(m^2 mV)

'HFP01SC calibration variables.

Dim shf_mV(4)
Dim shf_mV_run(4)
Dim shf_mV_0(4)
Dim shf_mV_180(4)
Dim shf_mV_end(4)
Dim V_Rf(4)
Dim V_Rf_run(4)
Dim V_Rf_180(4)
Dim shf_cal_on
Dim j

DataTable (mean,TRUE,100)
DataInterval (0,10,Min,10)

Average (4,hfp01sc_1,IEEE4,shf_cal_on)
Sample (4,shf_cal(1),IEEE4)
EndTable

Sub hfp01sc_cal

'Begin HFP01SC calibration on a fixed interval.

If ( IfTime (1,CAL_INTERVAL,Min) ) Then
shf_cal_on = TRUE
Move (shf_mV_0(1),4,shf_mV_run(1),4)
SW12 (TRUE)
EndIf

If ( IfTime (4,CAL_INTERVAL,Min) ) Then
Move (shf_mV_180(1),4,shf_mV_run(1),4)
Move (V_Rf_180(1),4,V_Rf_run(1),4)
SW12 (FALSE)
EndIf

15

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

If ( IfTime (19,CAL_INTERVAL,Min) ) Then
Move (shf_mV_end(1),4,shf_mV_run(1),4)

'Compute new calibration.

For j = 1 to 4
shf_cal(j) = (V_Rf_180(j)*V_Rf_180(j)*128.7)/ABS (((shf_mV_0(j)+shf_mV_end(j))/2)-shf_mV_180)
Next j
EndIf

'Stop filtering data.

shf_cal_on = FALSE

EndSub

BeginProg

'HFP01SC factory calibration in W/(m^2 mV) = 1000/sensitivity.

shf_cal(1) = 1 'Unique value.
shf_cal(2) = 1 'Unique value.
shf_cal(3) = 1 'Unique value.
shf_cal(4) = 1 'Unique value.

Scan (100,mSec,3,0)

'Measure the HFP01SC soil heat flux plates.

VoltDiff (shf_mV(1),4,mV50C,11,TRUE,200,250,1,0)

'Apply calibration to HFP01SC soil heat flux plates.

For j = 1 to 4
shf(j) = shf_mV(j)*shf_cal(j)
Next j

'Measure voltag e across the heate r (Rf_V).

VoltDiff (V_Rf(1),4,mV5000,17,TRUE,200,250,0.001,0)

'Maintain a 100 sample running average.

AvgRun (shf_mV_run(1),4,shf_mV(1),100)
AvgRun (V_Rf_run(1),4,V_Rf(1),100)

CallTable (mean)

Call hfp01sc_cal
NextScan

EndProg

16

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

TABLE 6A. Wiring for Example 4

Description Color CR10X A21REL-12

Sensor Signal #1 White 1H
Sensor Signal #2 White 1L
Sensor Signal #3 White 2H
Sensor Signal #4 White 2L
Sensor Signal #5 White 3H
Sensor Signal #6 White 3L

All Signal References Green AG

All Shields Clear G
Heater Resistor Signal #1 Yellow 4H
Heater Resistor Signal #2 Yellow 4L
Heater Resistor Signal #3 Yellow 5H
Heater Resistor Signal #4 Yellow 5L
Heater Resistor Signal #5 Yellow 6H
Heater Resistor Signal #6 Yellow 6L

All Heater Resistor Signal References Purple AG

All Shields Clear G

Sensor Power #1 Red REL 1 NO
Sensor Power #2 Red REL 1 NO
Sensor Power #3 Red REL 2 NO
Sensor Power #4 Red REL 2 NO
Sensor Power #5 Red REL 3 NO
Sensor Power #6 Red REL 3 NO

All Power Reference Black G

TABLE 6B. Wiring for Example 4

Description CR10X A21REL-12

Power 12V + 12V

Power Reference G GROUND

Control C8 CTRL 1
Control jumper from CTRL 2 to CTRL 1
Control jumper from CTRL 3 to CTRL 2

Power jumper from REL 1 COM to +12V
Power jumper from REL 2 COM to REL 1 COM
Power jumper for REL 3 COM to REL 2 COM

17

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

Example 4. Sample CR10X Program Using External Power and Relay

;{CR10X}
;
*Table 1 Program

01: 1 Execution Interval (seconds)

;Measure HFP01SC on smallest range.
;
1: Volt (SE) (P1)

1: 6 Reps
2: 22 7.5 mV 60 Hz Rejection Range
3: 1 SE Channel
4: 7 Loc [ shf_mV_1 ]
5: 1 Mult
6: 0 Offset

;Measure HFP01SC on larger range.
;
2: Volt (Diff) (P2)

1: 6 Reps
2: 23 25 mV 60 Hz Rejection Range
3: 1 DIFF Channel
4: 44 Loc [ shf_mV_1a ]
5: 1 Mult
6: 0 Offset

;Load in the factory calibration.
;
3: If (X<=>F) (P89)

1: 13 X Loc [ cal_1 ]
2: 1 =
3: 0 F
4: 30 Then Do

;Factory calibration in W/(m^2 mV) = 1000/sensitivity.
;
4: Z=F (P30)

1: 1 F ;<- Enter the unique calibration for plate 1 here
2: 0 Exponent of 10
3: 13 Z Loc [ cal_1 ]

5: Z=F (P30)

1: 1 F ;<- Enter the unique calibration for plate 2 here
2: 0 Exponent of 10
3: 14 Z Loc [ cal_2 ]

6: Z=F (P30)

1: 1 F ;<- Enter the unique calibration for plate 3 here
2: 0 Exponent of 10
3: 15 Z Loc [ cal_3 ]

7: Z=F (P30)

1: 1 F ;<- Enter the unique calibration for plate 4 here
2: 0 Exponent of 10
3: 16 Z Loc [ cal_4 ]

18

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

8: Z=F (P30)

1: 1 F ;<- Enter the unique calibration for plate 5 here
2: 0 Exponent of 10
3: 17 Z Loc [ cal_5 ]

9: Z=F (P30)

1: 1 F ;<- Enter the unique calibration for plate 6 here
2: 0 Exponent of 10

3: 18 Z Loc [ cal_6 ]
10: End (P95)
11: Beginning of Loop (P87)

1: 0 Delay

2: 6 Loop Count
;Apply custom calibration to raw soil heat flux measurement.

;
12: Z=X*Y (P36)

1: 7-- X Loc [ shf_mV_1 ]

2: 13-- Y Loc [ cal_1 ]

3: 1-- Z Loc [ shf_1 ]
13: End (P95)
;Output data.

;
14: If time is (P92)

1: 0 Minutes (Seconds --) into a

2: 20 Interval (same units as above)

3: 10 Set Outp ut Fl ag High (Flag 0)
15: Real Time (P77)

1: 0110 Day,Hour/Minute (midnight = 0000)
16: Resolution (P78)

1: 1 High Resolution
;Do not include that calibration data in the soil heat flux.

;
17: If Flag/Port (P91)

1: 18 Do if Flag 8 is High

2: 19 Set Intermed. Proc. Disable Flag High (Flag 9)
18: Average (P71)

1: 6 Reps

2: 1 Loc [ shf_1 ]
19: Do (P86)

1: 29 Set Intermed. Proc. Disable Flag Low (Flag 9)
20: Sample (P70)

1: 6 Reps
2: 13 Loc [ cal_1 ]

;Add other processing here.

19

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

;Call calibration routine.
;
21: Do (P86)

1: 8 Call Subroutine 8

*Table 2 Program

02: 0 Execution Interval (seconds)
*Table 3 Subroutines
;Calibration routine.

;
1: Beginning of Subroutine (P85)

1: 8 Subroutine 8
;Perform in-situ calibratation.

;
2: If time is (P92)

1: 1 Minutes (Seconds --) into a

2: 180 Interval (same units as above)

3: 30 Then Do
3: Beginning of Loop (P87)

1: 0 Delay

2: 6 Loop Count
4: Z=X (P31)

1: 7-- X Loc [ shf_mV_1 ]

2: 19-- Z Loc [ mV_0_1 ]
5: End (P95)
;Begin heating for calibration.

;
6: Do (P86)

1: 48 Set Port 8 High
;Used to filter data during and after calibration.

;
7: Do (P86)

1: 18 Set Flag 8 High
8: End (P95)
;End site calibration three minutes after calibration started.

;
9: If time is (P92)

1: 4 Minutes (Seconds --) into a

2: 180 Interval (same units as above)

3: 30 Then Do

20

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

;Measure voltage across curr ent shunt resistor d uring calibrati on.
;This measurement is used to compute power.
;
10: Volt (SE) (P1)

1: 6 Reps
2: 25 2500 mV 60 Hz Rejection Range
3: 7 SE Channel
4: 37 Loc [ V_Rf_1 ]
5: .001 Mult
6: 0 Offset

11: Beginning of Loop (P87)

1: 0 Delay
2: 6 Loop Count

12: Z=X (P31)

1: 7-- X Loc [ shf_mV_1 ]

2: 25-- Z Loc [ mV_180_1 ]
13: End (P95)
;Turn off the soil heat flux plate heaters.

;
14: Do (P86)

1: 58 Set Port 8 Low
15: End (P95)
;Compute in-situ calibration.

;
16: If time is (P92)

1: 39 Minutes (Seconds --) into a

2: 180 Interval (same units as above)

3: 30 Then Do
17: Do (P86)

1: 28 Set Flag 8 Low
18: Beginning of Loop (P87)

1: 0 Delay

2: 6 Loop Count
19: Z=X (P31)

1: 7-- X Loc [ shf_mV_1 ]

2: 31-- Z Loc [ mV_end_1 ]
20: Z=X*Y (P36)

1: 37-- X Loc [ V_Rf_1 ]

2: 37-- Y Loc [ V_Rf_1 ]

3: 13-- Z Loc [ cal_1 ]
21: Z=X*F (P37)

1: 13-- X Loc [ cal_1 ]

2: 128.7 F

3: 13-- Z Loc [ cal_1 ]

21

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

22: Z=X+Y (P33)

1: 19-- X Loc [ mV_0_1 ]
2: 31-- Y Loc [ mV_end_1 ]
3: 43 Z Loc [ work ]

23: Z=X*F (P37)

1: 43 X Loc [ work ]
2: .5 F
3: 43 Z Loc [ work ]

24: Z=X-Y (P35)

1: 43 X Loc [ work ]
2: 25-- Y Loc [ mV_180_1 ]
3: 43 Z Loc [ work ]

25: Z=ABS(X) (P43)

1: 43 X Loc [ work ]
2: 43 Z Loc [ work ]

26: Z=X/Y (P38)

1: 13-- X Loc [ cal_1 ]
2: 43 Y Loc [ work ]

3: 13-- Z Loc [ cal_1 ]
27: End (P95)
28: End (P95)
29: End (P95)
End Program

-Input Locations­1 shf_1
2 shf_2
3 shf_3
4 shf_4
5 shf_5
6 shf_6
7 shf_mV_1
8 shf_mV_2
9 shf_mV_3
10 shf_mV_4
11 shf_mV_5
12 shf_mV_6
13 cal_1
14 cal_2
15 cal_3
16 cal_4
17 cal_5
18 cal_6
19 mV_0_1
20 mV_0_2
21 mV_0_3
22 mV_0_4
23 mV_0_5
24 mV_0_6
25 mV_180_1

22

26 mV_180_2
27 mV_180_3
28 mV_180_4
29 mV_180_5
30 mV_180_6
31 mV_end_1
32 mV_end_2
33 mV_end_3
34 mV_end_4
35 mV_end_5
36 mV_end_6
37 V_Rf_1
38 V_Rf_2
39 V_Rf_3
40 V_Rf_4
41 V_Rf_5
42 V_Rf_6
43 work
44 shf_mV_1a
45 shf_mV_2a
46 shf_mV_3a
47 shf_mV_4a
48 shf_mV_5a
49 shf_mV_6a

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

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, ∆T
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 is given by:

CCCC C

=+ =+ρθ ρθρ (1)

()

sbdmw bdvww

ρ

w

θ

m

where C
of water, C
on a mass basis,
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
CS616 water content reflectometer. A value of 840 J kg
capacity of dry soil is a reasonable value for most mineral soils (Hanks and
Ashcroft, 1980).

θ

= (2)

v

ρ

b

is the heat capacity of moist soil, ρb is bulk density, ρw is the density

S

is the heat capacity of a dry mineral soil, θm is soil water content

d

θ

is soil water content on a volume basis, and Cw is the heat

v

, over the output

s

-1 K-1

for the heat

23

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

The storage term is then given by Eq. (3) and the soil heat flux at the surface is
given by Eq. (4).

TCd

∆

ss

S

=

t

GG S

=+

sfc cm

8

7. Maintenance

The HFP01SC requires minimal maintenance. Check the sensor leads monthly
for rodent damage.

8. In-Situ Calibration Theory

For detailed information on the theory of the in-situ calibration, see the Theory
section of the Hukseflux manual or visit the application section of the
Hukseflux web site at http://www.hukseflux.com/heat%20flux/applic&spec.pdf.

Equation 6 i n t he Hukseflux manual is used to compute a new calib ration every
three hours. The heater is on for a total of 180 seconds. Table 7 lists the
variables used in the Hukseflux manual and those in the example datalogger
programs.

(3)

(4)

TABLE 7. Hukseflux and Campbell Scientific

Variable Names

Description Hukseflux Campbell

Soil Heat Flux

Output of Sensor in mV V

1/Sensitivity 1/E

Output of Sensor during

ϕ

sen

sen2

V (0) mV_0

calibration at t=0 seconds

Output of Sensor during

V (180) mV_180

calibration at t=180 seconds

Output of Sensor after

V (360) mV_end

calibration and just before

output

Voltage Across fixed

Ω resistor

10

V

cur

Scientific

shf

shf_mV

cal

V_Rf

24

9. References

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

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.

25

Model HFP01SC Self-Calibrating Soil Heat Flux Plate

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