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Department of Soil, Water, and Climate, Univ. of Minnesota, 1991 Upper Buford Circle, St. Paul, MN 55018
*Corresponding author (reece{at}soils.umn.edu).
ABSTRACT
Time domain reflectometry (TDR) based electrical conductivity (EC) measurements underestimate solution conductivity (
) as salinity increases unless a correction parameter, Rcable, is incorporated into the EC calculation. The parameter Rcable accounts for series resistance of cable, connectors, and cable tester. The main objective of this study was to propose and verify a simple method of directly measuring Rcable from the load resistance on waveguides that are shorted together. Also, the dependence of Rcable on cable length vs. other resistances was investigated. The parameter Rcable was found to be a function of cable length and a constant probe resistance. Errors caused by ignoring Rcable in EC determinations increased with both salinity and series resistance. Although there may be cases where Rcable has a negligible effect on EC determinations, there are also situations where it is important. This study shows that the measurement of Rcable is so simple that there is little reason not to routinely incorporate it in all TDR-based EC determinations.
Received for publication October 3, 1996.
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