2 non-linear relationship, Non-linear relationship, At 21°c – Campbell Scientific 253-L and 257-L (Watermark 200) Soil Matric Potential Sensors User Manual
Page 24
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253-L and 257-L Soil Matric Potential Sensors
7.2.3.2 Non-Linear Relationship
For more precise work, calibration and temperature compensation in the range
of 10 to 100 kPa has been refined by Thompson and Armstrong (1987), as
defined in the non-linear equation,
]
)
01060
.
0
21
.
34
(
062
.
1
[
01306
.
0
s
s
s
R
T
T
−
+
−
2
s
R
SWP
=
where SWP is soil water potential in kPa
TABLE 7-3. Comparison of
Estimated Soil Water Potential
and R
s
at 21°C
kPa (Non-
Linear
Equation)
kPa
(Linear
Equation)
(R
s
)
kOhms
–3.7
1.00
–9 –11 2.00
–14 –18 3.00
–20 –26 4.00
–27 –33 5.00
–35 –41 6.00
–45 –48 7.00
–56 –56 8.00
–69 –63 9.00
–85 –70
10.00
–105 –78
11.00
–85
12.00
–92
13.00
–99
14.00
–107
15.00
–115
16.00
–122
17.00
–129
18.00
–144
20.00
–159
22.00
–174
24.00
–188
26.00
–199
27.50
18