Campbell CO2 User Guide

INSTRUCTION MANUAL

023/CO2 Bowen Ratio System

with CO2 Flux

Revision: 4/98

Copyright (c) 1994-1998

Campbell Scientific, Inc.

Warranty and Assistance

The 023/CO2 BOWEN RATIO SYSTEM WITH CO2 FLUX is warranted
by CAMPBELL SCIENTIFIC, INC. to be free from defects in materials and
workmanship under nor mal use and service for twelve (12) months from date of
shipment unless specifi ed 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 wi thin their territories. Please visi t www.campbellsci.com to
determine which Campbell Scientific company serves your country. 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.

023/CO2 BOWEN RATIO SYSTEM WITH CO2 FLUX

TABLE OF CONTENTS

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PAGE

SECTION 1. SYSTEM OVERVIEW

1.1 Review of Theory ....................................................................................................................1-1

1.2 System Description .................................................................................................................1-2

SECTION 2. LI-6262 INSTALLATION

2.1 Analyzer Preparation...............................................................................................................2-1

2.2 Initial Setup..............................................................................................................................2-1

SECTION 3. STATION INSTALLATION

3.1 Sensor Height and Separation................................................................................................3-2

3.2 Soil Thermocouples and Heat Flux Plates..............................................................................3-2

3.3 Wiring......................................................................................................................................3-3

3.4 Battery Connections................................................................................................................3-3

SECTION 4. SAMPLE 023/CO2 PROGRAM

4.1 Program Details ......................................................................................................................4-1

4.2 CR23X Program......................................................................................................................4-2

SECTION 5. STATION OPERATION

5.1 Pump.......................................................................................................................................5-1

5.2 Manual Valve Control..............................................................................................................5-1

5.3 Zero and Span Calibration ......................................................................................................5-1

5.4 Routine Maintenance ..............................................................................................................5-2

SECTION 6. CALCULATING FLUXES USING SPLIT

6.1 Webb et al. Correction............................................................................................................6-1

6.2 Soil Heat Flux and Storage .....................................................................................................6-2

6.3 Combining Raw Data ..............................................................................................................6-2

6.4 Calculating Fluxes...................................................................................................................6-2

APPENDIX

A. References.............................................................................................................................A-1

I

TABLES

1.2-1 Component Power Requirements.......................................................................................... 1-4

2.2-1 LI-6262 Analog Output Connections...................................................................................... 2-2

3.3-1 CR23X/Sensor Connections for Example Program............................................................... 3-4

4.1-1 Example LI-6262 Carbon Dioxide Coefficients ...................................................................... 4-2

4.2-1 Output From Example 023/CO2 Bowen Ratio System Program ........................................... 4-2

6.4-1 Input Values for Flux Calculations.......................................................................................... 6-3

6.4-2 Selected Code from CALCBRC.PAR with Unit Analysis........................................................ 6-4

FIGURES

1.2-1 Vapor Measurement System.................................................................................................. 1-2

1.2-2 Thermocouple Configuration.................................................................................................. 1-3

2-1 023/CO2 Bowen Ratio System............................................................................................... 2-1

2.2-1 LI-6262 and Mounting Hardware............................................................................................ 2-2

2.2-2 Plumbing Inputs ..................................................................................................................... 2-2

2.2-3 023/CO2 Plumbing, Valves, and Soda Lime and Desiccant Tubes....................................... 2-3

3-1 023/CO2 Bowen Ratio System with CO

3.2-1 Placement of Thermocouples and Heat Flux Plates.............................................................. 3-2

3.2-2 TCAV Spatial Averaging Thermocouple Probe...................................................................... 3-3

3.4-1 Terminal Strip Adapters for Connections to Battery............................................................... 3-3

5.3-1 Assembly for Spanning the LI6262 ........................................................................................ 5-2

Flux........................................................................ 3-1

2

II

SECTION 1. SYSTEM OVERVIEW

1.1 REVIEW OF THEORY

By analogy with molecular diffusion, the flux­gradient approach to vertical transport of an
entity from or to a surface assumes steady
diffusion of the entity along its mean vertical
concentration gradient.

When working within a few meters of the
surface, the water vapor flux density, sensible
heat flux, and carbon dioxide flux density, E, H,

may be expressed as:

and F

c

∂ρ

=

Ek

=ρ

HCk

Fk

cc

where
carbon dioxide density, C
air, T is temperature, z is height, and k

are the eddy diffusivities for vapor, heat, and

k

c

carbon dioxide respectively. Air density and the
specific heat of air should account for the
presence of water vapor. The eddy diffusivities
are functions of height. The vapor and
temperature gradients reflect temporal and
spatial averages.

Applying the Universal Gas Law to Eq. (1), and
using the latent heat of vaporization, λ, the
latent heat flux density, L
terms of mole fraction of water vapor (w).

Lk

ev

Here P is atmospheric pressure, R is the
universal gas constant, and M
weight of water. Similarly, Eq. (3) can be written
as:

Fk

cc

v

v

∂

z

∂

T

pH

∂

z

∂ρ

=

=λ

=

c

∂

z

is vapor density, ρ is air density,

ρ

v

PM

v

TRwz

∂

PMTRc

c

∂

∂

∂

z

is the specific heat of

p

, can be written in

e

is the molecular

v

is

ρ

c

, kH, and

v

(1)

(2)

(3)

(4)

(5)

where c is the mole fraction of carbon dioxide
and M

is the molecular weight of carbon

c

dioxide.
In practice, finite concentration gradients are

measured and an effective eddy diffusivity
assumed over the vertical gradient:

ev

=

HCk

ρ

TR

pH

PM

=

Lk

λ

PM

=

Fk

cc

TR

21

v

−

zz

()

12

−

TT

()

21

−

zz

()

12

−

cc

()

21

c

−

zz

()

12

(6)

(7)

(8)

−

ww

()

where the subscripts 1 and 2 refer to the upper
and lower arms respectively.

In general, k

and kH are not known but under

v

specific conditions are assumed equal. The
ratio of H to L

is then used to partition the

e

available energy at the surface into sensible and
latent heat flux. This technique was first
proposed by Bowen (1926). The Bowen ratio,

, is obtained from Eq. (6) and Eq. (7),

β

H

β

==

L

e

C

λε

−

TT

()

p

21

−

ww

()

21

(9)

where ε is the ratio of the molecular weight of
water vapor to dry air. The surface energy
budget is given by,

−=+, (10)

RGHL

ne

where R
is the total soil heat flux. R
into the surface and G, H, and L
away from the surface. Substituting βL
Eq. (10) and solving for L

L

e

is net radiation for the surface and G

n

−

RG

n

=

+1β

. (11)

and Fc are positive

n

e

yields:

e

are positive

for H in

e

1-1

SECTION 1. SYSTEM OVERVIEW

FIGURE 1.2-1 Vapor Measurement System

Sensible heat flux is found by substituting Eq.
(11) into Eq. (10) and solving for H.

=−− (12a)

HR GLE

n



=−−

HR G

n

RG




If the eddy diffusivity for carbon dioxide, k
assumed equal to k



−

n



+

1β



v (kH

), Fc can be found

(12b)

, is

c

using Eq. (13) and (8).

−

zz

()

12

=

k

c

TT

()

21

Measurements of R

−

H
C

ρ

p

and G, and the gradients

n

(13)

of w, T, and c are required to estimate latent
and sensible heat, and carbon dioxide flux.

Atmospheric pressure is also a necessary
variable, however, it seldom varies by more
than a few percent. It may be calculated for the
site, assuming a standard atmosphere, or
obtained from a nearby station and correcting
for any elevation difference.

The following equation can be used to estimate
the site pressure if the elevation is known:

PE=−

..

101325 1





44307 69231



5.25328






(14)

where P is in kPa and the elevation, E, is in
meters (Wallace and Hobbes, 1977).

Eq. (9) shows that the sensitivity of β is directly
related to the measured gradients; a 1% error in
a measurement results in a 1% error in β.

When the Bowen ratio approaches -1, the
calculated fluxes approach infinity. Fortunately,
this situation usually occurs during early
morning and late evening when the flux
changes direction and there is little available
energy, R

-1 (e.g., -1.25 < β < -0.75), L

- G. In practice, when β is close to

n

and H are

e

assumed to be negligible and are not
calculated. Ohmura (1982) describes an
objective method for rejecting erroneous Bowen
ratio data.

1.2 SYSTEM DESCRIPTION

1.2.1 WATER VAPOR AND CARBON DIOXIDE MEASUREMENTS

Carbon dioxide and water vapor concentrations
are measured with a single Infrared Gas
Analyzer (Model LI-6262, LI-COR Inc., Lincoln,
NE) (IRGA), using a technique developed for
multiple level gradient studies (Lemon, 1960).
Air samples from two heights are routed to the
IRGA (Figure 1.2-1). The IRGA continuously
measures the gradient between the two levels.

1-2

CR23X

SECTION 1. SYSTEM OVERVIEW

FIGURE 1.2-2. Thermocouple Configuration

Inverted Teflon filters (Gelman, ACRO50) with a
1 µm pore size prevent dust contamination of
lines and IRGA. They also prevent liquid water
from entering the system.

A single low power DC pump aspirates the
system. Manually adjustable flow meters are
used to adjust and match the flow rates. A flow
rate of 0.4 liters/minute is recommended. A
CR23X datalogger measures all sensors and
controls the valves that switch air streams
through the IRGA.

Every two minutes the air drawn through the
IRGA is reversed with the first valve. Forty
seconds is allowed for the pump to purge the
IRGA. One minute and 20 seconds of
measurements are made and averaged for
each two minute cycle.

The carbon dioxide and water vapor gradients
are measured every second. The average
carbon dioxide and water vapor gradients are
calculated every 20 minutes. At the top of every
hour the sample cell in the IRGA is scrubbed of
carbon dioxide and water vapor. The absolute
concentration of carbon dioxide and water vapor
is then measured by the IRGA.

1.2.2 AIR TEMPERATURE MEASUREMENT

The air temperature gradient is measured with
fine wire chromel–constantan thermocouples.
The thermocouples are wired into the
datalogger such that the temperature gradient is
measured differentially (Figure 1.2-2). The
differential voltage is due to the difference in

temperature between T

and T2 and has no

1

inherent sensor offset error. The datalogger
resolution is 0.006°C with 0.1 µV rms noise.

The thermocouples are not aspirated.
Calculations indicate that a 25 µm (0.001 in)
diameter thermocouple experiences less than

-1

0.2°C and 0.1°C heating at 0.1 m s

-1

1 m s
W m

wind speeds, respectively, under 1000

-2

solar radiation (Tanner, 1979). More

and

importantly, error in the gradient measurement
is due only to the difference in the radiative
heating of the two thermocouple junctions. The
physical symmetry of the thermocouple junction
minimizes this error. Conversely, contamination
of only one junction can cause large errors. A
pair of 76 µm (0.003 in) thermocouples with two
parallel junctions at each height are used to
make the temperature gradient measurement

Applying temperature gradients to the
thermocouple connectors was found to cause
offsets. The connector mounts were designed
with radiation shields and thermal conductors to
minimize gradients.

1.2.3 NET RADIATION AND SOIL HEAT FLUX

Net radiation and soil heat flux are averaged
over the same time period as the water vapor,
temperature, and carbon dioxide gradient.

To measure soil heat flux, heat flux plates are
buried in the soil at a depth of eight centimeters.
The average temperature of the soil layer above
the plate is measured using four parallel
thermocouples. The heat flux at the surface is

1-3

SECTION 1. SYSTEM OVERVIEW

then calculated by adding the heat flux
measured by the plate to the energy stored in
the soil layer. The storage term is calculated by
multiplying the change in soil temperature over
the averaging period by the soil heat capacity.

1.2.4. POWER SUPPLY

The current requirements of the components of
the 023/CO2 Bowen Ratio system are given in
Table 1.2-1.

TABLE 1.2-1. Component Power

Requirements

CURRENT

COMPONENT at 12 VDC

LI-6262 1000 mA

Pump 60 mA

CR23X 5 mA

Two large solar panels (60 watts or greater) and
a 70 amp-hour battery are capable of providing
a continuous current of 1.1 A, assuming 1000

-2

of incoming solar radiation for 12 hours a

Wm
day. The solar panels are required to keep a
full charge on the battery. The voltage of the
battery must be monitored by the station
operator. Do not allow the battery voltage to fall
below 11 VDC. If the battery voltage falls below
11 VDC, the IRGA will shut down. The station
operator must then manually reset the IRGA by
turning the power switch (on the front panel) off
and then on. A datalogger control port is used
to control power to the pump via relays.

1-4

SECTION 2. LI-6262 INSTALLATION

This section describes how the LI-6262 Infrared Gas Analyzer is integrated into the 023/CO2 enclosure.

ZERO SPAN

0

0

1

28

2

27

3

26

4

25

5

24

6

23

7

22

8

21

9

20

10

19

11

18

12

17

13

16

14

15

ZERO SPAN

0
0

1

28

2

27

3

26

4

25

5

24

6

23

7

22

8

21

9

20

10

19

11

18

12

17

13

16

14

15

0
0

28

27

26

25

24

23

22

21

20

19

18

17

16

15

0
0

28

27

26

25

24

23

22

21

20

19

18

17

16

15

CO /

1

2

3

4

5

6

7

8

9

CO

10

11

12

13

14

1

2

3

4

5

6

7

8

9

H O

10

2

11

12

13

14

H O ANALYZER

22

Model LI-6262

2

C2C2mV

m/m

LI-COR

339.48

R

ON

-5.250

123

FUNCTION

456

EXIT

789

0

ENTER

C

READYOFF

+12V
GROUND
GROUND
SOL 1+
SOL 1­GROUND
SOL 2+
SOL 2­GROUND
PUMP+
PUMP­GROUND
MIRROR+
MIRROR­GROUND
SOL 1 CTRL
SOL 2 CTRL
M&P OFF
M&P ON

BR RELAY DRIVER-12V

MADE IN USA

FIGURE 2-1. 023/CO2 Bowen Ratio System

2.1 ANALYZER PREPARATION

The LI-6262 has two inline Balston filters inside the
analyzer, ahead of the reference and sample cells.
These filters have high flow rates with low back
pressure. However, they have a time constant of
about a minute. To decrease the time constant of
the analyzer, replace the Balston filters with tubing.
The ACRO50 filters installed on the Bowen Ratio
arms will provide sufficient filtration for the LI-6262.
Section 7.5 of the LI-6262 manual provides more
information on removing the Balston filters.

CAUTION: Never operate the LI-6262
without adequate filtration ahead of the
reference and sample cells.

2.2 INITIAL SETUP

The LI-6262 is mounted on top of the black
bracket inside the 023/CO2 enclosure. It is held
in place by two mounting rails that are attached
to the bottom of the analyzer by four pan head
screws (Figure 2.2-1). It may be necessary to
relocate the rubber feet of the LI-6262 so they
do not interfere with the black mounting bracket.

MADE IN USA

+12V
GROUND
GROUND
SOL 1+
SOL 1­GROUND
SOL 2+
SOL 2­GROUND
PUMP+
PUMP­GROUND
MIRROR+
MIRROR­GROUND
SOL 1 CTRL
SOL 2 CTRL
M&P OFF
M&P ON

BR RELAY DRIVER-12V

CC / MIN.

AIR

X 100

10

8

6

4

2

REFERENCEREFERENCE

12

34

56

78

910

SE

1

2

3

4

HL

HL

HL

HL

HL

DIFF

13 14

15 16

17 18

19 20

21 22

SE

7

8

9

40

HL

HL

HL

HL

HL

DIFF

04:REF_TEMP
+21.93

CR23X MICROLOGGER

CS I/O

CC / MIN.

AIR

X 100

10

8

6

4

2

SAMPLESAMPLE

11 12

5

6

EX1

EX2

EX3

EX4

CAO1

CAO2P1P2P3P4

11

HL

23 24

12

HL

COMPUTER

RS232

POWER OUT CONTROL I/O

G5VG

SW12G12V

12VGC1C2C3C4GC5C6C7C8

SDM

1 2 3 A

4 5 6 B

7 8 9 C

0 # D

*

G 12V

POWER IN

G

GROUND

LUG

SN:

MADE IN USA

The 023/CO2 Bowen Ratio system requires that
the LI-6262 operate in differential mode (see
the LI-6262 manual for details). In this mode
carbon dioxide and water vapor are scrubbed
on the chopper input.

Prepare a soda lime and desiccant tube, as
described in Section 7.4 of the LI-6262 manual.
The bevaline tube that connects the soda lime
and desiccant tube to the LI-6262 chopper must
be replaced with longer tubes, to accommodate
mounting the desiccant tube to the enclosure
backplate. Attach the bottom hose (nearest the
soda lime) to the FROM CHOPPER fitting and
the top hose (nearest the perchlorate) to the TO
CHOPPER fitting (Figure 2.2-2). Install the tube
in the enclosure using the two clips mounted on
the left side of the backplate.

Every hour the sample cell of the analyzer is
scrubbed of carbon dioxide and water vapor
with external soda lime and desiccant tubes.
The absolute concentration of carbon dioxide
and water vapor is then measured by the
analyzer. The soda lime and desiccant tubes
are plumbed in series and are integrated into

2-1

SECTION 2. LI-6262 INSTALLATION

CO

2

H O

2

CO /2H O2ANALYZER

Model LI-6262

LI-COR

ON

OFF

FUNCTION
EEX

ENTER

CC / MIN.

AIR

X 100

10

8

6

4

2

CC / MIN.

AIR

X 100

10

8

6

4

2

REFERENCE SAMPLE

+12V
GROUND
GROUND
SOL 1+
SOL 1­GROUND
SOL 2+
SOL 2­GROUND
PUMP +
PUMP ­GROUND
MIRROR +
MIRROR ­GROUND
SOL 1 CTRL
SOL 2 CTRL
M&P OFF
M&P ON

BR RELAY DRIVER -12V

MADE IN USA

+12V
GROUND
GROUND
SOL 1+
SOL 1­GROUND
SOL 2+
SOL 2­GROUND
PUMP +
PUMP ­GROUND
MIRROR +
MIRROR ­GROUND
SOL 1 CTRL
SOL 2 CTRL
M&P OFF
M&P ON

BR RELAY DRIVER -12V

MADE IN USA

123A
456B
789C

*

0#D

1
2
3
4
5
6
7
8

9
10
11
12
13
14
15
16

DAC1 5V
DAC1 100mV
DAC1 20mA
SIG GND
DAC2 5V
DAC2 100mV
DAC2 20mV
SIG GND
CO 1S

H O 1S

TEMP 5V
SIG GND
AUX INPUT
CHASSIS GND

2

CO 4S

2

2

H O 4S

2

115

RS-232C DCE SAMPLE REFERENCE

IN

OUT

SCRUBBER TO

CHOPPER

AC

VOLTAGE

.25A/230V

.5A/115V

FROM
CHOPPER

10.5-16 VDC

2A

UNPLUG AC POWER BEFORE SERVICING TO PREVENT PERSONAL INJURY

WARNING!

LI-6262

CO /H O ANALYZER

2

2

MODEL
SR. NO.

LI-COR

U.S. Patent # 4,803,370

U.S. and Foreign Patents Pending

Made in U.S.A.

IRG3-2 2 9

LI-6262 Maintenance

Internal soda Lime/Desiccant must be
changed annually.

A range of time periods are given for
maintenance. Actual time period depends
on operating conditions.

External Soda Lime/Desiccant: weekly,
monthly
Internal Air Filters: monthly, yearly
Fan Air Filter: weekly, monthly
Factory Checkout: yearly

See operator's maunal for servicing
Internal components.

the system with a pair of quick connect
connectors.

Fill the tube with the female connector with soda
lime and the tube with the male connector with
magnesium perchlorate. Plumb the tubes as
shown in Figure 2.2-3. The tubes are attached
to the backplate with two pair of clips.

The analyzer's analog output is connected to
the CR23X datalogger with the 023/CO2 signal
cable. Table 2.2-1 describes the connections
on the analyzer end of the signal cable. Table

3.3-1 (Section 3) describes the connections on
the CR23X end of the cable.

TABLE 2.2-1. LI-6262 Analog Output

Connections

COLOR CONNECTION

CHANNEL
BLACK SIG GND 8
GREEN CO2 0.1 SEC 9
WHITE H2O 0.1 SEC 11
RED TEMP 5V 13
CLEAR CHASSIS GND 16

After the analyzer is plumbed and wired into the
023/CO2 system and the mounting rails are
fastened to the analyzer, slide the analyzer over
the black bracket as shown in Figure 2.2-1.
Line the push buttons with the holes on either
side of the bracket and press firmly until the
analyzer is seated on the bracket. Push the
buttons in until a click is heard and LI-6262 is
securely attached to the black bracket.

NOTE: The analyzer fits snugly within the
fiberglass enclosure. The zero and span
knobs will make contact with the inside of
the enclosure lid. With time, four black
rings will appear on the lid. The zero and
span knobs are not exposed to any
excessive stress when the lid is closed and
latched.

FIGURE 2.2-1. LI-6262 and Mounting

Hardware

2-2

To Sample Flowmeter

To Valve B

To Reference Flowmeter

To Zero Switch

FIGURE 2.2-2. Plumbing Inputs

Mount on Back Plate

To 12 VDC 70
Ahr (or greater)
Battery

Magnesium
Perchlorate

Fiberglass Wool

Soda Lime

Zero Switch

SECTION 2. LI-6262 INSTALLATION

Valve B

SOL 2-

To Sample In

SOL 2+

Upper Arm

To Reference In

Valve A

SOL 1-

Magnesium
Perchlorate

SOL 1+

Lower Arm

Soda Lime

CO2PUMB
(system)

FIGURE 2.2-3. 023/CO2 Plumbing, Valves, and Soda Lime and Desiccant Tubes

2-3

SECTION 3. STATION INSTALLATION

ers

Figure 3-1 shows the typical 023/CO2 system installed on a CM10 tripod. The 023/CO2 enclosure and
mounting arms mount to the tripod mast (1 1/2 in. pipe) with U-bolts. The size of the tripod allows the
heights of the arms to be adjusted from 0.5 to 3 meters. The mounting arms should be oriented due
south to avoid partial shading of the thermocouples.

Two solar panels (60 watts or greater) are mounted on a separate tripod or A-frame (not provided by
Campbell Scientific). The net radiometer is mounted on a separate stake (not provided by Campbell
Scientific). It should be positioned so that it is never shaded by the tripod and mounting hardware, and
such that the mounting hardware is not a significant portion of its field of view.

Other Sensors Not Shown:
(1) Wind Speed and Direction

Sensor

(1) Air Temperature and

Humidity Sensor

BOWENCO2
(system)

Intake
Filt

023/CO2 Enclosure

Type E Fine
Wire
Thermocouples

Averaging Soil
Temperature
Probe and Soil
Heat Flux Plates

Net Radiometer

CM10 Tripod

Grounding Rod

User Supplied deep cycle
battery (70 AHr or greater).
Two Solar Panels, 60 watts or
greater (not shown).

FIGURE 3-1. 023/CO2 Bowen Ratio System with CO2 Flux

3-1

SECTION 3. STATION INSTALLATION

3.1 SENSOR HEIGHT AND SEPARATION

There are several factors which must be
balanced against each other when determining
the height at which to mount the support arms
for the thermocouples and air intakes.

The differences in moisture, temperature, and
carbon dioxide increase with height, thus the
resolution of the gradient measurements
improves with increased separation of the arms.

The upper mounting arm must be low enough
that it is not sampling air that is coming from a
different environment up wind. The air that the
sensors see must be representative of the
soil/vegetation that is being measured. As a
rule of thumb, the surface being measured
should extend a distance upwind that is at least
100 times the height of the sensors. The
following references discuss fetch requirements
in detail: Brutsaert (1982); Dyer and Pruitt
(1962); Gash (1986); Schuepp, et al. (1990);
and Shuttleworth (1992).

The lower mounting arm needs to be higher
than the surrounding vegetation so that the air it
is sampling is representative of the bulk crop
surface, and not a smaller surface i.e. do not
place the lower arms in between the rows of a
row crop like sorghum.

The example SPLIT parameter file that
calculates the surface fluxes assumes a 1.0
meter arm separation. If your station is installed
with an arm separation other than 1.0 meter,
measure and note the separation. Be sure to
change the arm separation, DZ, in the SPLIT
parameter file CALBRC.PAR.

3.2 SOIL THERMOCOUPLES AND HEAT FLUX PLATES

The soil thermocouples and heat flux plates are
installed as shown in Figure 3.2-1. The TCAV
parallels four thermocouples together to provide
the average temperature, see Figure 3.2-2. It is
constructed so that two thermocouples can be
used to obtain the average temperature of the
soil layer above one heat flux plate and the
other two above the second plate. The
thermocouple pairs may be up to two meters
apart.

The location of the two 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.

Use a small shovel to make a vertical slice in
the soil and excavate the soil to one side of the
slice. Keep this soil intact so that it 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. Make a horizontal cut
eight cm below the surface with a knife into the
undisturbed face of the hole and insert the heat
flux plate into the horizontal cut. Press the
stainless steel tubes of the TCAVs above the
plates as shown in Figure 3.2-1. When
removing the thermocouples, grip the tubing,
not the thermocouple wire.

Install the CS615 as shown in Figure 3.2-1.
See the CS615 manual (Section 5) for detailed
installation instructions.

3-2

Up to 1 m

2.5 cm

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.

6 cm

2 cm

Ground Surface

8 cm

FIGURE 3.2-1. Placement of Thermocouples and Heat Flux Plates

FIGURE 3.2-2. TCAV Spatial Averaging

Thermocouple Probe

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

SECTION 3. STATION INSTALLATION

3.4 BATTERY CONNECTIONS

Two terminal strip adapters for the battery posts
(P/N 4386) are provided with the 023/CO2
(Figure 3.4-1). These terminal strips will mount
to the wing nut battery posts on most deep cycle
lead acid batteries.

The solar panels (60 watts or greater), BR relay
driver, LI-6262, and CR23X each have separate
power cables. Once the system is installed,
these power cables are then connected to the
external battery (red to positive, black to
negative). The CR23X power cable is shipped
in the 023/CO2 enclosure and must be
connected to the +12V (red from power cable)
and ground (black from power cable) terminals
on the CR23X wiring panel.

Several deep cycle batteries can be connected
in parallel, to provide power to the system
during cloudy or overcast days.

Finally, wrap the thermocouple wire around the
CR23X base at least twice before wiring them
into the terminal strip. This will minimized
thermal conduction into the terminal strip. After
all the connections are made, replace the
terminal strip cover.

3.3 WIRING

Table 3.3-1 lists the connections to the CR23X
for the standard 023/CO2 system using the
example program in Section 4. Because the air
temperature measurements are so critical, the
air temperature thermocouples are connected
to channel 4 (the channel that is closest to the
reference temperature thermistor). The input
terminal strip cover for the CR23X must be
installed once all connections have been made
and verified (Section 13.4.1 of the CR23X
manual).

Finally, wrap the thermocouple wire around the
CR23X base at least twice before wiring them
into the terminal strip. This will minimized
thermal conduction into the terminal strip. After
all the connections are made, replace the
terminal strip cover.

FIGURE 3.4-1. Terminal Strip Adapters for

Connections to Battery

The LI-6262 can not be turned on and off with
relays without a hardware modification to the
power board (contact LI-COR for details). After
the hardware modification has been made. A
Crydom D1D07 (P/N 7321) can be used to
power the LI-6262. The control side of the
D1D07 can be operated by a BR relay driver.
Do not power the LI-6262 through the BR relay
driver, because there is a 0.8 V drop through it
and the high current drain of the LI-6262 may
create an offset in single ended measurements.

3-3

SECTION 3. STATION INSTALLATION

TABLE 3.3-1. CR23X/Sensor Connections for Example Program

CHANNEL SENSOR COLOR
1H Q7.1 RED

1L Q7.1 BLACK

Q7.1 CLEAR

2H CS615 GREEN
2L WIND DIRECTION RED

CS615 BLACK/CLEAR
WIND DIRECTION WHITE/CLEAR

3H TCAV PURPLE
3L TCAV RED

TCAV CLEAR

4H UPPER 0.003 TC - CHROMEL PURPLE
4L LOWER 0.003 TC - CHROMEL PURPLE

AIR TEMP TCs - CONSTANTAN RED/RED

5H HFT3 #1 BLACK
5L HFT3 #1 WHITE

HFT3 #1 CLEAR

6H HFT3 #2 BLACK
6L HFT3 #2 WHITE

HFT3 #3 CLEAR

7H LI-6262 (CO2 0.1 Second) GREEN
7L LI-6262 (Signal low) BLACK

8H LI-6262 (H2O 0.1 Second) WHITE
8L LI-6262 (Jumper to 6L) BLACK

9H LI-6262 (Analyzer Temperature) RED
9L LI-6262 (Jumper to 7L) BLACK

LI-6262 (Ground) CLEAR

10H HMP45C (Temperature) YELLOW
10L HMP45C PURPLE

CLEAR

11H HMP45C (Relative Humidity) BLUE
11L JUMPER TO 10L JUMPER TO 10L

P1 WIND SPEED BLACK
GND WIND SPEED WHITE/CLEAR
EX2 WIND DIRECTION BLACK
+12 V CS615 RED

+12 V HMP45C RED
G HMP45C BLACK
+5 V HMP45C ORANGE

C1 PULSE FOR LOWER ARM TO REFERENCE

AND UPPER ARM TO SAMPLE ORANGE w/ WHITE

C2 PULSE FOR UPPER ARM TO REFERENCE

AND LOWER ARM TO SAMPLE BLUE w/ WHITE
C3 PULSE TO END SCRUB WHITE w/ ORANGE
C4 PULSE TO SCRUB WHITE w/ BLUE

3-4