Environmental Engineering Reference
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obtained from the TD/FD approach; and 2) the modeled reflection scattering
parameter obtained from the implemented TL model of the probe plus LUT,
S
11
,
MOD
(
f
)
.
It is worth pointing out that, for this specific monitoring purpose, the TL model
includes has to include not only the Cole-Cole parameters of the LUT as minimiza-
tion variables, but also some lumped circuit elements that account for additional
parasitic effects that cannot be compensated for through traditional SOL calibration
procedures.
This procedure was first tested and validated on well-referenced liquids, and suc-
cessively it was applied for the evaluation of the Cole-Cole parameters of oils. The
main steps of the procedure are similar to those in the diagram in Fig. 3.19 and will
be described in detail in the following subsections.
To define the performance characteristics of this combined approach (particu-
larly, in terms of repeatability and uncertainty), a rigorous metrological validation
was also carried out through measurements on well-referenced materials.
TDR measurements on vegetable oils were carried out through the TDR80E04.
However, in view of possible practical implementation, it is worth underlining that
the procedure described herein also apply for portable TDR instrumentation.
4.4.1
Design of the Measurement Cell and Transmission Line
Modeling
Although the SOL calibration is the first strategy for reducing the systematic er-
ror contributions, a further accuracy enhancement must take into account the par-
asitic effects associated with the measurement cell. For this purpose, an accurate
TL modeling of the specific measurement cell represents a successful key for a fur-
ther enhancement of the final measurement accuracy. The implemented TL model
must include all the undesired effects (e.g., undesired impedance mismatches) that
inevitably influence the measurements.
A picture of the probe designed for this specific application is shown in Fig. 4.11.
Fig. 4.11
Picture of the
used coaxial probe
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