A combined Wenner-array/heat dissipation sensor for measuring electric conductivity and moisture of soils.

This paper presents the characterization results and proposes a technique for the compensation of measurement drifts observed in heat dissipation soil moisture sensors when repeated measurements with a small time interval (less than 15 minutes) is used. A heat dissipation sensor was fabricated using the center probes of a conventional electrical conductivity Wenner-array probe. Several experiments were conduct, using two types of soils, with different sampling frequency of data, from 5 to 15 minutes. It is observed that the drift of the measured values depends strongly on the type of soil, since for a clay loam soil the errors due to the repetition of measurements with short time intervals result in a much more humid soil indication than the correct value, while for a sandy loam exactly the opposite behavior is verified. Based on experimental measured data for each type of soil, it is proposed a correction technique to compensate for errors present in repeated measurements.