AF043-01
US Patent 5148125
Revision Date: 14 March, 2001
5
Converting the Signal to Soil Moisture
There are two methods to convert the output signal into soil moisture and current. The
simplest is to use the graph below, alternatively use the formula following the graph. Two
curves are included:
1. Sand, silt and sandy or silty loam soils
2. Clay and clay loams.
Aquaflex Frequency Output Sensor Calibration Graph
0
10
20
30
40
50
60
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95 100 105 110 115 120 125 130
Sensor Output (pulses per minute)
V
o
lu
m
e
tr
ic
S
o
il
M
o
is
tu
re
(
%
)
Sand/silt
Clay
Use the following equations to convert the output into soil moisture
For Sand, silt and sandy and silty loams:
Moisture (%)
= 0.5 x (ppm-10)
For Clay and clay loams:
Moisture (%)
= -4.9 + 0.51 x ppm + 0.0026 x ppm² - 0.0000205 x ppm³
where ppm = pulses per minute
