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Measuring Soil Matric Potential in situ by Sensing Heat Dissipation within a Porous Body: I. Theory and Sensor Construction
Author(s) -
Phene C. J.,
Hoffman G. J.,
Rawlins S. L.
Publication year - 1971
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1971.03615995003500010015x
Subject(s) - calibration , dissipation , water potential , porosity , porous medium , water content , materials science , sensitivity (control systems) , soil water , mechanics , range (aeronautics) , relaxation (psychology) , environmental science , soil science , thermodynamics , geotechnical engineering , composite material , electronic engineering , physics , engineering , psychology , social psychology , quantum mechanics
A matric potential sensor is described that measures heat dissipation to sense the water content of a porous block in equilibrium with soil. It consists of a P‐N junction diode that is surrounded by a heating coil and embedded in a porous medium. A theoretical model is developed that describes the sensor in terms of its limiting parameters. Geometry, size, rate of heat input, and duration of heating are chosen to obtain a certain degree of accuracy and to make the measurements independent of the surrounding soil. Construction, calibration, measurement, and temperature correction techniques are described. Since the electrical output of the sensor is linear with temperature, a single calibration curve is adequate at all temperatures within the accuracy reported. By varying the composition of the porous body, the range and sensitivity of the sensor can be altered.