Modeling a Coated Coaxial Time Domain Reflectometry Probe response in High Electrical Conductivity Solutions
Location
Eccles Conference Center
Event Website
http://water.usu.edu/
Start Date
3-27-2006 10:40 AM
End Date
3-27-2006 10:45 AM
Description
The ubiquitous application of time domain reflectometry (TDR) in the measurement of water content in the near subsurface is inhibited in samples with high electrical conductivity (EC). TDR waveforms show a loss of signal amplitude in a saline (ionic) environment due to the decrease of the number of polarizable molecules as described in the imaginary term of the complex dielectric permittivity. Recent studies have shown that coated TDR probes allow the determination of permittivity in solutions with high EC, but extracting the medium permittivity from the TDR signal requires more research. The objectives of this study were: (i) to measure effective permittivities in highly saline solutions using coated probes and (ii) apply transmission line theory on a coated coaxial probe for modeling the solution permittivity. A 12 cm long coaxial TDR probe with a center-rod sheathed with two different thicknesses of PTFE tubing (εr=2.1) was connected to a Textronix 1502B cable tester. The TDR wave acquisition program WinTDR was used to collect a 1004-point wave trace each for the saline solution with EC ranging from 1 to 350 dS m-1. The transmission line model describes the effect of the coatings on the apparent dielectric permittivity of the solution. The measured data was fitted to a multi-section scatter function (MSSF) model to obtain a correlation and to correct the apparent dielectric permittivity to its true value. The motivation of the study is to facilitate accurate water content determination in saline environments using coated probes.
Modeling a Coated Coaxial Time Domain Reflectometry Probe response in High Electrical Conductivity Solutions
Eccles Conference Center
The ubiquitous application of time domain reflectometry (TDR) in the measurement of water content in the near subsurface is inhibited in samples with high electrical conductivity (EC). TDR waveforms show a loss of signal amplitude in a saline (ionic) environment due to the decrease of the number of polarizable molecules as described in the imaginary term of the complex dielectric permittivity. Recent studies have shown that coated TDR probes allow the determination of permittivity in solutions with high EC, but extracting the medium permittivity from the TDR signal requires more research. The objectives of this study were: (i) to measure effective permittivities in highly saline solutions using coated probes and (ii) apply transmission line theory on a coated coaxial probe for modeling the solution permittivity. A 12 cm long coaxial TDR probe with a center-rod sheathed with two different thicknesses of PTFE tubing (εr=2.1) was connected to a Textronix 1502B cable tester. The TDR wave acquisition program WinTDR was used to collect a 1004-point wave trace each for the saline solution with EC ranging from 1 to 350 dS m-1. The transmission line model describes the effect of the coatings on the apparent dielectric permittivity of the solution. The measured data was fitted to a multi-section scatter function (MSSF) model to obtain a correlation and to correct the apparent dielectric permittivity to its true value. The motivation of the study is to facilitate accurate water content determination in saline environments using coated probes.
https://digitalcommons.usu.edu/runoff/2006/AllPosters/5