Time Domain Reflectometry Technique for Monitoring of Liquid Characteristics

Time domain reflectometry (TDR) technique is widely used in hydrology and soil science for accurate and flexible soil water content measurements. The most attractive advantages concerning the considered TDR measurement system are: good precision and accuracy, high reliability of the measuring head, a unique approach of pulsing a long coaxial probe and analysing the reflected voltage signature caused by changes in impedance, capability of multiplexing several probes, possibility of remotely acceding, controlling and electronically retrieving and transmitting data through existing telecommunication technologies. A time domain reflectometer transmits the incident signal, an ultra short rise time (200 ps), step voltage pulse, along the transmission line and records the travel time and the magnitude of all reflected signals (echo) returning from the controlled system. Changes in impedance (capacitance, inductance and resistance) causing electromagnetic discontinuities that reflect voltage can be located, particularly, for liquid level and dielectric properties monitoring purposes. The above mentioned discontinuities result from impedance changes produced by changes in the dielectric constant. The time domain reflectometry method used in this research has the purpose to monitor the behavior of different liquid substances, detecting their levels and giving information about their characteristics, such as volumetric content, dielectric constant, electrical conductivity, as well as the identification of different interfaces. Furthermore, the main objective of the present work is to develop an interpretation method for the analysis of TDR signal that, associated with a simple calibration procedure and with a suitable probe design can ensure, at the same time, quantitative and qualitative liquid monitoring.