Enhanced reflectometry measurements of permittivities and levels in layered petrochemical liquids using an "in-situ" coaxial probe

Measurement and control of the fluid parameters play a very important role in industry applications such as in the petrochemical industrial processing, where there is an increasing demand for real-time determination of dielectric parameters in relation to the product quality. Furthermore, in such a context, additional stringent requirements frequently deal with the spatial localization of non-miscible-layered liquids, like water layers often present in the bottom of tanks during the refinery industrial processing. Recently, reflectometry has become a very attractive method for monitoring applications, thanks to its accuracy and flexibility performance. In this paper, the design of a suitable probe configuration and an associated calibration structure, both leading to an optimal experimental set-up for practical reflectometry measurements in petrochemical industrial applications, are illustrated. Moreover, starting from frequency-domain reflectometry data, a robust optimization procedure is implemented and experimentally tested, thus allowing the accurate evaluation of the frequency-dependent dielectric properties and of multiple levels in different stratified liquids. Results derived through the simple time-domain technique are compared with those achieved through two different frequency-domain approaches, involving the Fast Fourier Transformation (FFT) of time-domain reflectometry (TDR) data and direct vector network analyzer (VNA) measurements, respectively. It is demonstrated that the frequency-domain approaches can significantly enhance the measurement accuracy, allowing the estimation of fuel level with an uncertainty lower than 0.5 mm. Furthermore, it is also shown that a low-cost TDR system, combined with an appropriate FFT-based algorithm, can be successfully adopted for the simultaneous measurement of permittivity and levels, without substantially affecting the measurement accuracy performance when compared to the direct frequency-domain VNA measurements.