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United States Department of Agriculture

Agricultural Research Service

Title: Time Domain Reflectometry (Tdr) System Manual

Author
item Evett, Steven

Submitted to: Electronic Publication
Publication Type: Book / Chapter
Publication Acceptance Date: December 20, 2000
Publication Date: N/A

Interpretive Summary: Automatic measurement of soil water content and salinity is important in many fields of engineering, agriculture (particularly irrigation control), resource management, and environmental monitoring. Time domain reflectometry (TDR) is increasingly used for these measurements because it can give accurate water contents in a wide range of soils and can be automated. The TDR System Manual contains eight chapters detailing, 1) assembly of a TDR measurement system, 2) running the TACQ computer program for system control and determination of soil water content, salinity levels, and temperature, 3) design and construction of required electrical cables, 4) installation of TDR probes and cables, 5) installation of multiplexers for automatic measurement with up to 256 probes, 6) electrical power provision and power control for remote solar-powered systems, 7) TDR principles and methods, and 8) hardware modifications. Included in the 112 page book are 88 illustrations and 4 tables. The TDR system described ensures accurate water content determination for a wide range of soils from clay to sand, and for a wide range of soil conditions from air dry to completely wet. It is suitable for low-power, unattended field systems, as well as laboratory systems. It works with and controls equipment from six manufacturers, including that designed by the author. The system has been used in an automatic irrigation system, in a remote, solar-powered crop water use measurement system, and in agriculture, resource management, and environmental monitoring work by researchers and engineers in the US and several countries. The book may be downloaded at http://www.cprl.ars.usda.gov/programs/

Technical Abstract: Measurement of soil water content, temperature, and salinity is important in many fields of engineering, agriculture (particularly irrigation control), resource management, and environmental monitoring. Time domain reflectometry (TDR) is often used in these endeavors because it can give accurate water contents in a wide range of soils and can be automated. The eTDR System Manual describes a software and hardware system for measurement of soil water content, bulk electrical conductivity, and temperature. Its eight chapters detail, 1) quick assembly and use of a TDR measurement system, 2) running the TACQ computer program for system control and data acquisition, 3) construction of required electrical cables, 4) installation of TDR probes and cables, 5) installation of multiplexers for automatic measurement with up to 256 probes, 6) electrical power provision and power control for remote solar-powered systems, 7) TDR principles and waveform interpretation methods, and 8) hardware modifications. The TDR system ensures accurate water content determination in a wide range of soils from clay to sand, and for a wide range of soil conditions from air dry to completely wet. It is suitable for low-power, unattended field systems, as well as laboratory systems. It works with and controls equipment from six manufacturers. The system has been used in an automatic irrigation system, in a remote, solar-powered crop water use measurement system, and in agriculture, resource management, and environmental monitoring work by researchers and engineers in the US and several countries. Multiplexer, probe, and cable designs were put on the market through a Cooperative Research and Development Agreement with Dynamax, Inc. of Houston, Texas. The chapters may be downloaded from http://www.cprl.ars.usda.gov/programs/

Last Modified: 8/29/2014
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