International Society for Industrial Process Tomography

Correction of Phase Errors due to Leakage Currents in Wideband EIT Field Measurements on Soil and Sediments

E. Zimmermann¹*, J. A. Huisman², A. Mester¹ and S. van Waasen^{1, 3}

¹ Central Institute for Engineering, Electronics and Analytics, Electronic Systems (ZEA-2), Forschungszentrum Jülich GmbH, Jülich, Germany

² Institute of Bio- and Geosciences, Agrosphere (IBG-3),
Forschungszentrum Jülich GmbH, Jülich, Germany

³ Faculty of Engineering, Communication Systems,
University of Duisburg-Essen, Duisburg, Germany

^*Email: e.zimmermann@fz-juelich.de

ABSTRACT

Electrical impedance tomography (EIT) is a promising method to characterize biogeochemical processes and important hydrological properties of soil, sediments, and rocks. The characterization is mainly based on the analysis of the phase response of the complex electrical conductivity in a broad frequency range (i.e. mHz to kHz). However, it is a challenge to measure the small phase response of low-polarizable soils and rocks in the higher frequency range up to 10 kHz where advanced measurement and model-based data correction methods are needed. In order to achieve the required phase accuracy, an optimized measurement system and advanced processing methods have been developed to correct several system-dependent errors. Recently, EIT measurements at test sites with low conductivity have shown a new dominating phase error related to capacitive leakage currents between cable shields and soil. In order to correct this phase error, we developed an advanced FEM model that considers both leakage currents and capacitive coupling between the soil and the cable shields in the reconstruction of the electrical conductivity distribution. By applying this improved method, the new dominating error could greatly be reduced. The investigation also showed that the leakage current is an additional indicator for data errors that can be used for data filtering. After application of the data filter and the error correction, the phase error of the measured transfer impedances at 10 kHz was reduced by at least a factor of 6. In addition, the physically implausible positive phases were effectively eliminated. The new correction method now enables the reconstruction of the complex electrical conductivity for frequencies up to 10 kHz at field sites with a low electrical conductivity.

Keywords Electrical impedance tomography, leakage current, capacitive coupling, inductive coupling

Industrial Application General