Convert Sm200 Voltages To Soil Moisture Readings - Delta-T Devices SM200 Quick Start Manual

5

Convert SM200 voltages to soil moisture readings

Note: The SM200 output is automatically converted to soil moisture when using an
HH2 meter or Delta-T data loggers.
Take a reading with the SM200
either
Convert the reading to √ε using the polynomial or
linearisation table below.
Then convert √ε to soil moisture,
calibration values (
or
Convert directly for mineral or organic soils
Conversion to √ε
Polynomial
(use for SM200 readings from 0 to 1.1 Volts)
ε
= +
1 0 . 16 . 103
where V is the SM200 output in volts
Linearisation table
√ε
V
0.000 1.011
0.030 1.447
0.060 1.832
0.090 2.168
Conversion from √ε to Soil Moisture
Soil moisture
Use these generalised soil calibration values for
mineral and organic soil types, or carry out a soil-
specific calibration to derive your own values – see SM200 User Manual.
Multiply x100 to convert soil moisture from m
Direct conversion for Mineral and Organic soils
θ
= −
. 0 071
mineral
θ
= −
. 0 039
organic
© 2005 Delta-T Devices Ltd
a a
,
).
0 1
−
2
V 38 . 725 V
(use for SM200 readings from 0 to 1.2 Volts)
√ε
V
0.120 2.461 0.260
0.150 2.718 0.310
0.180 2.946 0.400
0.220 3.211 0.600
( )
θ ε
= −
a a
0
+ −
. 1 917 V . 4
+ −
. 2 091 V . 5 029
θ
, using the soil
+ −
3
60 . 881 V 46
√ε
V V
3.442 0.820
3.700 0.960
4.105 1.040
4.953 1.100
1
3 -3
.m to % volumetric.
+
2 3
61 V . 7 248
+
2 3
V . 7 907 V
Example
V
= 0.294 volts
√ε
= 3.62
θ
=
24.0%
(for mineral soil)
θ
= 24.0%
+
4
. 032 V 13 . 536
√ε
V
5.936 1.150
6.586 1.200
6.991 1.220
7.333 1.800
a
0
Mineral 1.6
Organic 1.3
− +
4
. 5 48 V . 1 611
− +
4
. 5 978 V . 1 758
5
V
√ε
7.661
8.039
8.264
9.000
a
1
8.4
7.7
5
V
5
V
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