Abstract:
Heat dissipation sensors operate based on the temperature dependence of the transient heat conduction within the soil, which is a function of the soil characteristics and...Show MoreMetadata
Abstract:
Heat dissipation sensors operate based on the temperature dependence of the transient heat conduction within the soil, which is a function of the soil characteristics and its water content. After a heat pulse with controlled energy is applied to a heater, it is possible to show that the maximum temperature rise ATM measured in the temperature sensing element can be related to the volumetric water content of the soil θv [m3 m-3]. The design and fabrication of a low-cost soil moisture multiprobe heat pulse sensor system using conventional printed circuit boards and surface-mount devices is presented. The proposed sensor is free of the needles' deflection problem present in conventional multiprobe sensors and is manufactured using conventional off-the-shelf electronic components. A precision lowpower electronic signal conditioning circuit, using an instrumentation switched-capacitor building block, was developed and successfully used in the prototype. Due to an energy-efficient topology for the sensor and a low-power signal conditioning circuit, the average current consumption of the system (with one measurement per day) is only 3 μA. To demonstrate the feasibility of the concept, a prototype of the sensor was tested in soils with volumetric humidity in the range from θv = 0.05 m3 m-3 to θv = 0.41 m3 m-3 and, with a very low heating energy pulse (3 J), showed a sensitivity, normalized by the total energy applied, Γ = 211 × 10-3 °C m3 m-3 J-1. Compared with a button heat pulse probe sensor which has Γ = 192 × 10-3 °Cm3 m-3 J-1, the developed sensor shows a higher normalized sensitivity.
Published in: IEEE Transactions on Instrumentation and Measurement ( Volume: 68, Issue: 2, February 2019)