PRACTICAL CONSIDERATIONS FOR USING A TDR CABLE TESTER

Citation
Dk. Cassel et al., PRACTICAL CONSIDERATIONS FOR USING A TDR CABLE TESTER, Soil technology, 7(2), 1994, pp. 113-126
Citations number
NO
Categorie Soggetti
Geosciences, Interdisciplinary","Water Resources
Journal title
ISSN journal
09333630
Volume
7
Issue
2
Year of publication
1994
Pages
113 - 126
Database
ISI
SICI code
0933-3630(1994)7:2<113:PCFUAT>2.0.ZU;2-X
Abstract
Time domain reflectometry (TDR) technology can be used to measure soil water content, but due to an incomplete understanding of this technol ogy, some scientists are still reluctant to adopt it. The objectives o f this paper are to discuss the basic principles of TDR to measure soi l water content, to present the equations to convert TDR screen readin gs to soil water content values, and to describe a custom built TDR sy stem. Commercial cable testers operate under the assumption the dielec tric constant of the medium is known. For soils applications the diele ctric constant varies with soil water content and is unknown. The equa tions which govern the TDR technology presented in logical order allow the user to understand the relationships between wave velocity, diele ctric constant, and soil water content. The custom-built TDR system de scribed herr uses a commercially available cable tester; a balun trans former, shielded, two-wire transmission cable; and wave guides constru cted from stainless steel welding rod. Several of these systems have b een successfully used for six years.