Issues for calibration of thermal dissipation sensors for measuring matric suction

Thermal dissipation sensors (TDS) are used for continuous and long-term in situ measurement: of matric suction. This paper addresses some important issues regarding calibration of TDSs and parametric equations are explored. Different test methods used to obtain calibration parameters are evaluated and recommendations are also given. The dry soil method and vacuum saturation method are found to be appropriated to completely dry and saturate the TDS, respectively. The study suggests that a calibration can be done by measuring completely dry TDS, saturated TDS, and the air entry suction of the TDS if a generalized shape parameter or function exists. Finally, a new generalized calibration equation is proposed to improve the fitting to the calibration data. Good agreement was found with direct matric suction measurements in the low suction range (< 1 MPa). The TDS cannot be used to measure a suction < 10 kPa.