Table 5. Correcting readings of insulated probes to read the same
as the uninsulated readings. (The test material is methanol.)
Box 2
C
insulated = 139.9 pF = CT
C
uninsulated = 249.96 pF = CDW
hence Ci = CDW CT/(CDW CT)
Since with the insulated probe: CT = 139.9 pF
CDW = 249.6 pF
and with uninsulated probes:
Ci = 249.6 139.9/(249.6139.9) = 318.3 pF
The 318.3 pF may now be used to correct the capacitance calculated for the
insulated probes:
Cc = 318.3 C/(318.3C)
Note that Cair = same as for uninsulated = 3.1 pF
Cc = 91.9 pF
K = 29.6 [i.e., K = 91.9/(3.1)]
Probe
U
C = 71.3
C = 70.1
Cc = 89.9 pF
K = 29.0
M
C = 71.5
Cc = 92.2 pF
K = 29.7
Cc = 90.2 pF
K = 29.1
C = 70.3
average
K = 29.3
Box 3
C insulated = CT = 147.1 pF
C uninsulated = CDW = 336.5 pF
Ci = 261.3 pF
Cair = 4.2 pF
Probe
M
C = 87.7
Cc = 132.0 pF
K = 31.4 [i.e., K = 132.0/(4.2)]
C = 87.2
Cc = 130.8 pF
K = 31.1
U
C = 87.8
Cc = 132.2 pF
K = 31.5
C = 86.8
Cc = 130.0 pF
K = 30.9
average
K = 31.2
Box 4
C insulated = CT = 128.3 pF
CDW = 238.3 pF
Ci = 277.9 pF
Cair = 2.99 pF
Probe
M
C = 64.9
Cc = 84.7 pF
K = 29.3 [i.e., K = 84.7/(2.99)]
C = 65.0
Cc = 84.4 pF
K = 28.3
U
C = 64.2
Cc = 83.5 pF
K = 27.9
C = 64.2
Cc = 83.5 pF
K = 27.9
average
K = 28.1
of water were added in steps to obtain a curve of
from this data, and the temperatures at each probe
percent dry weight vs. dielectric constant. The
depth are shown in Appendix C. The depths for
dielectric constant was calculated using the
the probes, identified in Appendix C as F47, F01,
method described as procedure 2 in the preced-
and F42, are as follows:
ing section. This procedure corrects the capaci-
tance measurements made by an insulated probe
Probe F47--6 in. (15.25 cm) below the surface
to values similar to those of an uninsulated probe
Probe F01--12 in. (30.5 cm) below the surface
by assuming a series capacitance in the probe
Probe F42--18 in. (45.75 cm) below the surface.
itself. The value of this assumed capacitance is
determined by using water as a reference mate-
Calibration
rial. The actual equations used for these calcula-
Three calibration runs were made using a test
tions are shown in Table 6. After all three
apparatus in which an insulated test probe was
calibration runs were completed, it was discov-
embedded in a test jig with a known volume that
was filled with a sample of the test site soil. The
ered that a procedural error invalidated the data
weight of this test soil was also determined. At
taken in run 1. Since this data had to be rejected,
the start of a calibration run the soil was com-
calibration equations were generated for run 2
pletely dry. Known weights (and hence volumes)
and run 3. A composite equation using data from
11
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