SM150T User Manual 1.0
Operation
24
Calibration
The SM150T is provided with general calibrations for
mineral
and
organic
soils which can be used to convert the output from the
sensor directly into soil moisture when used with Delta-T loggers
and moisture meters. This section explains how these calibrations
work, how to adapt them for other soils and how to provide
calibrations for other data loggers.
The SM150T measures volumetric soil moisture
, by detecting the
dielectric properties of the damp soil
– the permittivity,
, or more
conveniently the
refractive index
, which is closely equivalent to
.
The SM150T response is best understood in these stages:
0.0
2.0
4.0
6.0
8.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
So
il
r
e
fr
ac
ti
ve
in
d
e
x
(√
ε
)
SM150T output (Volts)
SM150T dielectric performance
0%
20%
40%
60%
80%
0.0
0.2
0.4
0.6
0.8
1.0
θ
SM150 output (V)
SM150 soil moisture reading
Organic
Mineral
0.0
2.0
4.0
6.0
8.0
0%
20%
40%
60%
80%
√ε
θ
(%vol)
Soil calibrations
1. Soil calibration
θ ε
V
ε
2. Sensor calibration
3. Soil moisture reading
V
θ
