EC-5 6 CALIBRATION
permittivity is given by:
ε = 1/(−1.10570 x 10
−9
∗ RAW
3
+ 3.575 x 10
−6
∗ (1)
RAW
2
− 3.9557 x 10
−3
∗ RAW + 1.53153)
where RAW is the output from the Decagon data logger using 3V
excitation. If you are using a non-Decagon data logger, dielectric
permittivity is given by
ε = 1/(−3.3326 x 10
−9
∗ mV
3
+ 7.0218 x 10
−6
∗ mV
2
− (2)
5.11647 x 10
−3
∗ mV + 1.30746)
Mineral Soils
According to our tests, a single calibration equation generally suf-
fices for all mineral soil types with electrical conductivities from 0.1
dS/m to 10 dS/m saturation extract. VWC (θ) is given by:
θ = 8.5 ∗ 10
−4
∗ RAW − 0.48 (3)
where RAW is the output from the Decagon data logger using 3 V
excitation. If you are using a non-Decagon data logger, VWC is given
by:
θ = 11.9 ∗ 10
−4
∗ mV − 0.401 (4)
where mV is the output of the sensor when excited at 2,500 mV.
Please note that the equation reachs a maximum at ∼60% VWC
in pure water. To display data on a scale from 0 to 100%, VWC
should be modeled with a quadratic equation (which would result in
a 100% VWC in water), but a linear equation fits the mineral soil
VWC range as well as the quadratic, and linear equations are easier
to deal with, especially since mineral soil typically saturates at ∼40
to 50% VWC.
Potting soil
The following equations can be used to convert EC-5 output to water
content in potting soil. We tested several types of potting soil (Sun-
shine mix, Miracle Grow Potting Mix, and Custom Nursery soil) at
several salinities and found that VWC is given by:
θ = 1.3 x 10
−3
∗ RAW − 0.696 (5)
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