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2 The TRIME-T3 Tube Access Probe
2.1 Introduction
The measuring of soil water content with Time Domain Reflectometry is now a well established
method. However water content profiling is not possible with conventional TDR rod probes. The TRIME
tube probe was developed for this reason.
Since 1994 the TRIME-T3 has found numerous applications in earth and environmental sciences,
fulfilling even the most exacting requirements.
2.2 Measuring Field
The effective penetration depth of the probe is about 15 cm with the highest sensitivity in the
immediate vicinity of the access tube and decreases exponentially with distance. Figure 3 shows the
electric field distribution of the probe and the approximate measuring volume.
equipotential lines
effective measurement volume
aluminum plates
Figure 1: Electric field distribution of the TRIME probe and approximate measuring volume.
The elliptical measuring volume enables a higher representation to be achieved by several
measurements rotating the probe after each measurement and calculating the mean value.
The following experiment illustrates the high penetration depth of the measuring field:
In a bucket of 50 cm diameter filled with water saturated glass beads a moisture of 44 vol.-% is
measured. Measuring in a smaller bucket (see Fig. 3) would result in essentially lower measuring
values due to an amount of air within the measured volume.
Figure 2: Influence of a too small measuring volume on water content determination.
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