TCAV – Averaging Soil Thermocouple Probe
2
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.
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.
Partial emplacement of the HFP01 and the TCAV
sensors is shown for illustration purposes. All
sensors must be completely inserted into the soil face
before the hole is backfilled.
