Modeling, simulation and testing of a silicon soil moisture sensor based on the dual-probe heat-pulse method

A silicon soil moisture sensor, based in the dual-probe heat-pulse (DPHP) method, was modeled, simulated and tested for achieving, with low-cost, accurate and reliable measurements. This method is based on the application of a heat pulse during a fixed interval of time. The maximum rise in temperature (ΔTM) is monitored by the measurement probe, placed at a certain distance of the heater source. A low-cost high-performance and small temperature sensor (a dynamic VPTAT generator) was designed and fabricated to be placed into the probe which have 0.912 mm inner diameter and 20 mm long. If one considers the range of water contents, ratio of water mass to dry soil mass, in a typical agricultural soil (0.05–0.35m3 m−3), the average sensitivity of the dual probe is about 1.95º C per unit change (m3 m−3) in water content for q = 400 Jm−1