TDR Moisture Estimation for Granular Materials: An Application in Agro-Food Industrial Monitoring

Time-domain reflectometry (TDR) is a well-established technique for continuous monitoring of the moisture levels and dielectric properties of materials; typically, it is widely used in soil science applications. Despite the high flexibility, elevated accuracy, and the low cost of TDR instrumentation, the state of the art is actually rather lacking in specific applications for the quality monitoring of agro-industrial processes and agro-food products. Therefore, the possibility of real-time control of moisture level plays a crucial role in terms of optimization, quality preservation, and energy saving in several industrial applications. In this regard, the development of suitable models relating the dielectric properties of granular materials to their moisture content is a still an open issue. To fill this gap, in this paper, the authors study the feasibility of adopting the TDR technique for such a purpose. The proposed goal is successfully reached through a comparative analysis among different calibration procedures and through experimental measurements on various granular materials. Finally, the adopted methodology is assessed through a rigorous metrological characterization, thus allowing the evaluation of the associated measurement uncertainty and repeatability.