Improving a Dual-Probe Heat Pulse based soil moisture sensor using insulated nichrome wire

Abstract

The Dual-Probe Heat-Pulse technique has been widely used for in-situ moisture sensing. In the heater probe described in our earlier work the power consumption was 350 mW-the lowest in this category of sensors. In this paper, by employing a material selection method, we further improve the performance of the sensor by employing Parylene-coated nichrome wire and different packaging methods. The power consumption is reduced to 165 mW with a temperature rise between 1 K to 6.2 K degrees in 34% wet and dry red soils, respectively. A variant of the nichrome sensor was one that employed a ceramic tube with four longitudinal holes that eliminated the need for Parylene coating. The sensor was verified in agar agar solution and calibrated with 1200 kg/m2 red field soil. The compact packaging of the nichrome heater allowed us to provide a heat distribution of 3267 J/m on the probe surface which is two times more than the earlier attempts.