Environmental Engineering Reference
In-Depth Information
4.2.3
Validation of the Method on Dielectric Liquids
The TDR-based method was tested on four liquids (with different levels), which
were representative of 'high' (de-ionized water), 'medium' (acetone), and 'low'
(diesel oil and fuel) permittivity values. These liquids have negligible ionic con-
ductivity and relaxation effects in the considered frequency range (0-1.7 GHz). The
liquids were placed inside a cylindrical sample holder, and their level (
H
ref
)was
measured directly from the reading of the 1000 ml-graduated sample holder.
TDR measurements were performed through the HL1500; the number of mea-
surement averages for the acquisition was 10, and the number of acquired points
was 2048. The TDR waveforms for the considered liquids are shown in Fig. 4.4.
The significant reflections, clearly shown by the derivative curves, correspond to
coaxial cable-to-probe connection, to the air-liquid interface, and to the probe-end
point. The distance differences between the probe-end peaks and the air-liquid in-
terface peaks (located through the analysis of derivative data for each sample), give
the apparent liquid lengths.
It is important to point out that, for evaluating the dielectric constant from (4.1),
the reflection coefficient value should be retrieved from the steady-state portion of
the TDR waveform, as long as the low-loss non-dispersive liquid assumption can be
considered valid.
0.2
0.2
probe e
n
d
end of c
a
ble
0.0
0.0
-0.2
probe end
-0.2
-0.4
-0.4
liquid
interface
-0.6
-0.6
air/liqui
d
interfac
e
-0.8
-0.8
4
5
6
7
8
3.5
4.0
4.5
5.0
5.5
6.0
apparent distance (m)
apparent distance (m)
(b)
(a)
0.6
0.6
probe
end
0.4
air/liqui
d
interface
0.4
probe
end
air/liquid
interface
0.2
0.2
0.0
0.0
-0.2
-0.4
-0.2
3.5
4.0
4.5
5.0
3.5
4.0
4.5
5.0
apparent distance (m)
(c)
apparent distance (m)
(d)
Fig. 4.4
TDR waveform (
black line with dots
) and derivative of data (
gray
line
).
a
for a 41.3 cm level of de-ionized water sample [probe completely full].
b
for 27.2 cm
level of acetone sample.
c
for 32.1 cm level of fuel sample.
d
for 27.8 cm level of diesel oil
sample
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