PNNL

Abstract

Heat dissipation sensors, also known as heat dissipation units (HDUs), are used to measure soil matric potential at a much higher value than tensiometers. The process for calibrating these sensors uses a pressure plate apparatus (PPA) to remove water to a certain calibration point that is controlled by pressure. Conventionally, the pressure within the PPA is released before the temperature change calibration points are measured (deltaT0). This conventional HDU calibration in a PPA can take several weeks. In this note, it is proposed that the equilibrated temperature change at pressure (deltaTp) be corrected empirically to the value at zero pressure. Based on measurements of 14 HDUs between 0.2 and 1.0 bar, deltaTp was 6.2% larger than deltaT0 on average. After pressure correction using an empirical equation, the difference between the corrected deltaTp and deltaT0 was only to 0.28%. Without the need of pressure release to zero, the pressure-corrections method is expected to be faster than the conventional method.