Campbell TCAV Product Manual

TCAV

Averaging Soil

Thermocouple Probe

Revision

Copyright ©
Campbell Scientific, Inc.

: 7/18

1990 – 2018

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Safety

DANGER — MANY HAZARDS ARE ASSOCIATED WITH INSTALLING, USING, MAINTAINING, AND WORKING ON OR AROUND

TRIPODS, TOWERS, AND ANY ATTACHMENTS TO TRIPODS AND TOWERS SUCH AS SENSORS, CROSSARMS, ENCLOSURES,
ANTENNAS, ETC. FAILURE TO PROPERLY AND COMPLETELY ASSEMBLE, INSTALL, OPERATE, USE, AND MAINTAIN TRIPODS,

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CHECK WITH YOUR ORGANIZATION'S SAFETY COORDINATOR (OR POLICY) FOR PROCEDURES AND REQUIRED PROTECTIVE
EQUIPMENT PRIOR TO PERFORMING ANY WORK.

Use tripods, towers, and attachments to tripods and towers only for purposes for which they are designed. Do not exceed design limits.
Be familiar and comply with all instructions provided in product manuals. Manuals are available at www.campbellsci.com or by
telephoning [phone] (USA). You are responsible for conformance with governing codes and regulations, including safety
regulations, and the integrity and location of structures or land to which towers, tripods, and any attachments are attached. Installation
sites should be evaluated and approved by a qualified engineer. If questions or concerns arise regarding installation, use, or
maintenance of tripods, towers, attachments, or electrical connections, consult with a licensed and qualified engineer or electrician.

General

• Prior to performing site or installation work, obtain required approvals and permits. Comply

with all governing structure-height regulations, such as those of the FAA in the USA.

• Use only qualified personnel for installation, use, and maintenance of tripods and towers, and

any attachments to tripods and towers. The use of licensed and qualified contractors is highly
recommended.

• Read all applicable instructions carefully and understand procedures thoroughly before

beginning work.

• Wear a hardhat and eye protection, and take other appropriate safety precautions while

working on or around tripods and towers.

• Do not climb tripods or towers at any time, and prohibit climbing by other persons. Take

reasonable precautions to secure tripod and tower sites from trespassers.

• Use only manufacturer recommended parts, materials, and tools.

Utility and Electrical

• You can be killed or sustain serious bodily injury if the tripod, tower, or attachments you are

installing, constructing, using, or maintaining, or a tool, stake, or anchor, come in contact with
overhead or underground utility lines.

• Maintain a distance of at least one-and-one-half times structure height, 20 feet, or the distance

required by applicable law, whichever is greater, between overhead utility lines and the
structure (tripod, tower, attachments, or tools).

• Prior to performing site or installation work, inform all utility companies and have all

underground utilities marked.

• Comply with all electrical codes. Electrical equipment and related grounding devices should be

installed by a licensed and qualified electrician.

Elevated Work and Weather

• Exercise extreme caution when performing elevated work.

• Use appropriate equipment and safety practices.

• During installation and maintenance, keep tower and tripod sites clear of un-trained or non-

essential personnel. Take precautions to prevent elevated tools and objects from dropping.

• Do not perform any work in inclement weather, including wind, rain, snow, lightning, etc.

Maintenance

• Periodically (at least yearly) check for wear and damage, including corrosion, stress cracks,

frayed cables, loose cable clamps, cable tightness, etc. and take necessary corrective actions.

• Periodically (at least yearly) check electrical ground connections.

WHILE EVERY ATTEMPT IS MADE TO EMBODY THE HIGHEST DEGREE OF SAFETY IN ALL CAMPBELL SCIENTIFIC PRODUCTS,
THE CUSTOMER ASSUMES ALL RISK FROM ANY INJURY RESULTING FROM IMPROPER INSTALLATION, USE, OR
MAINTENANCE OF TRIPODS, TOWERS, OR ATTACHMENTS TO TRIPODS AND TOWERS SUCH AS SENSORS, CROSSARMS,
ENCLOSURES, ANTENNAS, ETC.

Table of Contents

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1. Description ................................................................. 1

2. Using the TCAV with Soil Heat Flux Plates .............. 1

2.1 Installation............................................................................................ 2

2.2 Calculating Soil Heat Flux ................................................................... 3

Figures

1-1. TCAV Thermocouple Probe ................................................................ 1

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

i

TCAV – Averaging Soil Thermocouple
Probe

1. Description

The TCAV is a temperature probe which parallels four thermocouple junctions
into one. One channel is required to measure the output voltage which
represents the average temperature of the four junctions. The TCAV is most
often used to obtain the average temperature of a soil layer for use in
calculating stored energy.

The probe is constructed with type E thermocouple wire (chromel-constantan)
and can be measured with one of the datalogger thermocouple measurement
instructions, TCSe() or TCDiff(). TCDiff() is recommended because it reduces
noise and ground loop problems.

2. Using the TCAV with Soil Heat Flux Plates

FIGURE 1-1. TCAV Thermocouple Probe

The TCAV is used in conjunction with soil heat flux plates to calculate the heat
flux at the surface of the soil. The plates are buried at a fixed depth of between
5 and 8 cm to reduce errors due to vapor transport of heat.

1

TCAV – Averaging Soil Thermocouple Probe

Partial emplacement of the HFP01 and the TCAV

sensors must be completely inserted into the soil face

2.1 Installation

The TCAV and two heat flux plates are typically installed as in FIGURE 2-1.
The TCAV is constructed so 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. One datalogger channel is required to measure the
output voltage which represents the average temperature of the four junctions.
The thermocouple pairs may be up to one meter apart.

sensors is shown for illustration purposes. All

before the hole is backfilled.

FIGURE 2-1. Placement of Thermocouples and Heat Flux Plates

The location of the two heat flux plates/thermocouples should be chosen to be
representative of the area under study. If the ground cover is extremely varied,
it could be necessary to have additional sensors to provide a valid average.

Use a shovel to cut a vertical slice in the soil and remove the soil to one side of
the cut. Try to keep the soil that is removed intact so that it can be replaced
with as little disruption as possible.

The sensors are installed in the undisturbed face. The depths are measured
from the top of the soil. A horizontal cut is made with a knife to install a heat
flux plate. The stainless steel tubes encasing the thermocouple junctions are
pressed into the soil, keeping the tubes horizontal. (When removing the
thermocouples, grip the tubing, not the thermocouple wire.)

To minimize thermal conduction down the sensor lead wires, wrap them
around the edge of the hole keeping the leads at the same level as the sensor for
as long as possible. Replace the soil in the same position as it was. Do not run
the leads directly to the surface.

2

2.2 Calculating Soil Heat Flux

The soil heat flux at the surface is calculated by adding the measured flux at a
fixed depth (in this case 8 cm) to the energy stored in the layer above the heat
flux plates. The heat capacity of the soil and the change in temperature over the
output interval are required to calculate the average stored energy, S (W m

S = (T

– T

) • D • Cs / t

i

i–1

Where:

T

is the current temperature (°C),

i

is previous temperature (°C),

T

i–1

D is depth to heat flux plate (m),

is the soil heat capacity (J m–3 °C–1), and

C

s

T is the time interval (s).

TCAV – Averaging Soil Thermocouple Probe

–2

):

One method of calculating Cs is to add the specific heat of the dry mineral soil,

–1

Csd, to that of the soil water, Cw (4190 J kg

–1

and Cw are on a mass basis (J kg

–3

on a volume basis (J m

°C–1) is:

°C–1). Cs, the heat capacity of the moist soil

°C–1). The values used for Csd

Cs = BD • (Csd + W • Cw)

This calculation requires site specific inputs for bulk density (BD, kg m

–3

),

mass basis water content (W, kg water/kg soil), and Csd, the specific heat of

–1

the dry soil. 840 J kg

°C–1 is a reasonable value for Csd for most mineral soils
(Hanks and Ashcroft, Applied Soil Physics, Published by Springer-Verlag,
New York, 1980).

3

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