Campbell Scientific TCAV-Averaging Soil Thermocouple Probe is a device that can be used to measure the average temperature of a soil layer. It is constructed with Type E thermocouple wire and can be measured with one of the datalogger thermocouple measurement instructions, 13 or 14. Instruction 14, which uses the differential voltage measurement, should be used to reduce noise and ground loop problems. The TCAV is often used in conjunction with soil heat flux plates to calculate the heat flux at the surface of the soil.
TCAV
AVERAGING
SOIL
THERMOCOUPLE
PROBE
INSTRUCTION
MANUAL
June
13, 1990
COPYRIGHT
(c)
1990, CAMPBELL
SCIENTIFIC'
lNC.
WARRANTY
The
TCAV
-
AVERAGTNG SOIL
THERMOCOUPLE
PROBE is warranted against
defects
in materials and
workmanship. This
warranty
applies
for twelve months
from
date of shipment.
We
will repair
or
replace
products
which
prove
to
be defective
during
the warranty
period
provided
they
are
returned
prepaid
to
CAMPBELL SCIENTIFIC,
lNC.
CAMPBELL
SCIENTIFIC,
lNC. will return
warranted equipment
by surface
carrier
prepaid.
No
other
warranty
is
expressed
or
implied.
CAMPBELL
SCIENTIFIC,
lNC.
is not liable
for
consequential
damages.
Products may not be
returned without
prior
authorization.
To
obtain
a
Returned Materials
Authorization
(RMA),
contact
CAMPBELL SCIENTIFIC,
lNC.,
phone (801)
753-2342.
An RMA number
will be
issued in
order
to facilitate
Repair Personnel in
ldentifying
an
instrument
upon
arrival.
Please write
this number
clearly
on
the
outside of
the
shipping
container.
CAMPBELL SCIENTIFIC,
lNC.
does
not
accept collect
calls.
Non-warranty
products
returned
for repair
should be
accompanied
by a
purchase
order
to cover
the
repair.
GAMPEIELL
SiCIENTIFIC,
llVG.
P.O.
Box 551
Logan, UT 84321
Phone
(801)
753-2342
TLX 453058
FAX
801-752-3268
Phone
(403)
461-5158
TLX 037-2966
(EDM)
FAX 403-450-2531
Phone 01
1 44509601
1 41
TLX 94016393
(CAMP
G)
FAX 01 1 44509601 091
9525 41st
Avenue
14-20
Field Street
Edmonton,
Alberta
TOE
5X7
Shepshed,
Leics.
LE12
gAL
CANADA
ENGLAND
1.
DESCRIPTION
The
TCAV ls a
temp€rature
probe
whlch
parallels
4
thermocouple
lunctbns
Into
one.
One
channd
ls
requlred to
measurs
the output
voltage
whlch
representE
the avelage
temp€rature
of
the four
lunctlons.
The
TCAV
ls most often
used
to obtaln
the average
temperature
d
a soll
layer for use
In
calculatlng
sfiored
energy.
The
probe
ls
constructed
with tYPe
E
thermocouple
wlre
(chromdconstantan) and
can
be
measured
with one
of
the datalogger
thermoco.rple
measuremsnt
Instructlons,
13 or
14. lnstruction
14,
whlch uses
the
dlfferentlal
voltage
measurement,
should
be used
to
reduce
noise
and
grourd
loop
problems.
FIGURE
1.
TCAV
ThermocouPle
Probe
USING
THE
TCAV
WITH SOIL
HEAT
FLUX
P1ATES
The TGAV
ls
used
in
conlunalon
with
soil
heat
flLD(
datss
to
calculate
the heat
flLD( at
the surface
of
the
soll.
The
plates
are
burled at
a
fked depth
of
betrren
5 and
8 cm
to reduce erorc
due
to
vapor transpott
cf
heat.
TCAV.
AVERAGING
SOIL
THERMOCOUPLE
PROBE
HI
LO
2.1 INSTALIATION
The
TCAV and
two
heat
ffrx
flates
are
typically
installed
as
in Flgure
2.
The TCAV
is
constructed
so
two thermocouples
can
be
used
to
obtain
the
average
temperature
of
the soil
layer
above one
heat flu(
plate
and
the other
two above
the
second
plate.
The thermocouple
pairs
may be
up
to two
m€|ters apalt.
FIGURE
2.
Placement
ot
Thermocouples
and
Heat
Flux
Plates
The
locatlon d
the
two
heat
flu
plates/thermocoupes
should
be
chosen
to be
representatlve
of
the area
under
study.
lf the
ground
corer
ls
extremely
varled,
it
could
be
necessaryto
have additlonal
sensors
to
provide
a wlH
avenge.
Use a
shovd
to
cut
a
vertlcal slice
in
the
soil
and
remo/e
the soil
to
one
slde
of
the
cut.
Try to
keep
the soll
that
ls remored
lntact so
that
it
can
be
replaced
with as
litde disruptlon
as
possible.
The
sensors
are
Installed
In the undisturbed
face.
The depths
are
measured
from
the
top of
the
so[.
A
horlzontal cut
ls made
wlth a
knife
to
Install a
heat
fru
plate.
The stainless
steel
tubes
encaslng
the
thermocouple
iunctions
are
pressed
Into the
soil,
keeplng
the
tubes
2.
SOIL,
SURFACE
HEAT
FLUX
PLATE
TCAV.
PROBE
horizontal.
(When
rernovlng
the thermocouples,
grip
the
tubing, not the thermocouple
wlre.)
To minimize
therrnal
conduction
down
the
sensor
lead wires,
wrap them
around
the edge cf
the
hole
keeplng
the leads
at
the
same
levd
as
the
sensor
for
as
long
as
possiHe.
Replace the
soll
in the
same
posftion
as
it was.
Do
not run the
leads
directly
to the
surftace.
2.2 CALCUI.ATING
SOIL
HEAT FLUX
The
soil
heat ffu
at
the
surface
ls
calculated
by
adding
the measured flu
at
a
fked
depth
(in
thls
case
I cm)
to the
energy stored
In the layer
above
the heat flu
plates.
The heat
capacity
of
the
soil and
the change
In temperature
over
the
output
interval
are
required to
cElculate
the
average stored energy, S
(W
m''):
S=(t'fTlr)*D*Cs/t
Where:
Tg is the
current
temperature
fC),
T;-1 is
prevlous
temperature
("C),
D is
depth
to heat flu
plate
(m),.'
^
Cs
is
the
soll
heat
capacity
d
r€
oGl;,and
T
is
the time interval
(s).
One
method
of calculatlng Cs
ls
to add
the
specific
heat
of
the
dry
mineral
spi! C$d,
to that
of
the
soilwater, C\,y
(4190
J
kg-'
'C').
The
values
used
for
Csd and
Or are on a
mass
basls
(J
kg-1
oC
1).
Cs,
the heat
qapncJty
of
the
molst
soil
on a
volume
basis
(J
m{
uC.'}
ls:
cs=BD*(Csd+W*GV)
This calculatlon
requireg
slte speciffc
lnputs for
bulk
density
(BD,
kg m{), mass
baslswater
content
(W,
kg water/kg
soll), and Cs{,
th€{
specific
heat
of
the
dry so[. 840 J
kg-'
"C'
is
a
reasonable
value for
Csd
for most mlneral
solls
(Hanks
and
Ashcrdt, Applled
Soll
Physlcs,
Published by Sprlnger-Verlag,
Now York, 1980).
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2
3
4
5
6
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