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Title: CAPACITANCE SENSOR FOR SOIL MOISTURE MEASUREMENT
Accession Number: 00099655
Record Type: Component
Availability: Find a library where document is available Abstract: Moisture content is an important parameter that controls the performance of earth materials. Because satisfactory techniques were not available, this study was undertaken to develop new instrumentation that could be permanently installed in highway substructures for long-term monitoring of moisture content. Moisture content determination requires that the amount of water and the dry weight in a given volume of soil be obtained. This study considered only the amount of water. A concept that involved the relationship between the amount of water in soil and the dielectric constant, an electrical property, was investigated. The electrical capacitance (C) of a pair of electrodes with moist material between them is related to to the dielectric constant (K) by C equals (Alpha times Epsilon) K, where Alpha is a constant based on the geometry of the electrodes and Epsilon is the permittivity of the vacuum. So that instrumentation problems encountered in the measurement of capacitance and dielectric constant with laboratory methods used in the field could be overcome, the sensor electrodes and soil were incorporated in the resonance circuit whose frequency of oscillation is a function of the circuit components. The measured output is the difference between the frequency in soil and in an electonic reference substituted for the soil. The curcuit design was first tested with the electrodes forming a container into which soil could be placed. Several configurations of the embedded sensor were designed and tested. The capacitance concept was useful for sensing change in the amount of moisture per unit volume of soil.
Supplemental Notes: Publication of this paper sponsored by Committee on Environmental Factors Except Frost. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
Monograph Title: Monograph Accession #: 00131138
Corporate Authors: Transportation Research Board 500 Fifth Street, NW Authors: Selig, Ernest TWobschall, Darold CMansukhani, SundruMotiwala, ArifPagination: pp 64-76
Publication Date: 1975
Serial: Conference:
54th Annual Meeting of the Transportation Research Board
Location:
Washington District of Columbia ISBN: 0309023807
Media Type: Digital/other
Features: Figures
(16)
; References
(5)
TRT Terms: Uncontrolled Terms: Subject Areas: Geotechnology; Highways
Files: TRIS, TRB
Created Date: Nov 5 1975 12:00AM
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