TDR Sensor Models:
Acclima offers three TDR sensor models: The TDR315H, the TDR310H and the TDR305H. These all
incorporate the same technology in waveform generation and capture. They are all designed for
operation in any soil texture. They differ in waveguide dimensions and optimum application.
TDR315H Description and Installation:
The TDR315H uses a 15 cm waveguide with a rod spacing of 1.9 cm. Because of its larger waveguide it
has the largest measuring volume of the three sensors
–
than being on the order of 100 ml. It can be
installed in any orientation but is usually installed by forcing the waveguide rods into the sidewall of a
trench that has been dug to the desired depth of installation. This method results in a horizontal
installation in undisturbed soil. A special rod guide supplied by Acclima is used to keep the rods parallel
while forcing them into the trench sidewall. It can also be installed in the center of a trench and then be
backfilled. With this method the backfill needs to be compacted to avoid air pockets near the waveguide
and to prevent the creation of a preferential path for surface water to percolate down to the sensor.
When the installation is complete the entire soil volume removed to create the trench must be placed
back into the trench with sufficient compaction that the backfilled trench surface is even with the
surrounding soil surface.
TDR315H Optimum Application:
The TDR315H provides excellent readings in all types of soils and has the advantage of a larger sampling
volume than the TDR310H and TDR301H. Because of the higher impedance waveguide and the longer
waveguide length the waveform is more susceptible to attenuation by soil ions than is the case with the
TDR310H and TDR305H. Hence the TDR315H is not recommended for use where the salt content of the
soil is exceedingly high. For saturated paste extraction electrical conductivity readings in excess of 10
dS/m the repeatability of the readings may degrade and even fail.
TDR310H Description and Installation:
The TDR310H uses a 10 cm waveguide with a rod spacing of 1.14 cm. The round form factor was
designed to match the diameter of a 1” schedule 40 PVC pipe. The top shoulder of the sensor can be
