Improving the Calibration of Surface Time Domain Reflectometry Sensors for Assessing the Moisture of Building Materials Taking into Account Signal Attenuation.

The article describes the problem of moisture in buildings and building materials as well as the Time Domain Reflectometry (TDR) measurement technique that can be applied for invasive and also noninvasive measurements of building materials. Moisture readings in such media rely on signal propagation time shift analysis and may be subject to errors, while the vast majority of models derived for TDR devices are based on this type of measurement. Multiple linear regression (MLR) is proposed as a method to improve the quality of the readouts achieved using TDR noninvasive sensors. The aim of this work was to improve the calibration methods of TDR surface sensors by taking into account the attenuation of the electromagnetic pulse caused by the presence of water and salt ions and to develop calibration formulas that are multiple linear regression equations considering both the time shift and signal attenuation. Within the research, two types of noninvasive TDR sensors were applied to measure the moisture of red ceramic, clinker and silicate bricks. Average RMSE values for all sensors and materials were 0.009 cm3/cm3 lower in the case of the proposed multiple regression calibration models and 0.005 cm3/cm3 in terms of RSE compared to the traditional calibration methods used in the TDR technique.