General calibration of capacitance soil moisture sensor for various electrical conductivity conditions
2009
Miyamoto, H.(Saga Univ. (Japan). Faculty of Culture and Education) | Cho, H. | Ito, Y. | Chikushi, J. | Eguchi, T.
The effect of electrical conductivity on voltage response of an EC-5 sensor, being a recent model of ECH2O soil moisture probes (Decagon Devices, Inc.) with 70 MHz signal generation circuit, has been investigated by calibrating the relationship between its output voltage (V) and volumetric water content (theta) in saline sand with different pore water electrical conductivities (sigmasub(W)): 0.030, 2.6, and 10 dS/m. In theta = 0.15 cubic m/cubic m, the EC-5 sensor could accurately determine theta from V-value obtained using a unique linear expression provided by its manufacturer. However, different V-values can be led depending on electrical conductivity even at identical moisture condition. To save additional calibration work of the EC-5 at given sigmasub(W), we proposed a new calibration model using three sets of known V vs. theta, and investigated its effectiveness. Although a few data sets are required for the modeling, it was found that the model can ensure high-accurate and repeatable estimation of theta by the EC-5 sensor. The method shown here may make it possible to calibrate any capacitance soil moisture probes quite easily for soils with a specified sigmasub(W).
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