Capacitance probe
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Capacitance sensors use capacitance to measure the dielectric permittivity of the surrounding medium. The volume of water in the total volume of soil most heavily influences the dielectric permittivity of the soil because the dielectric of water (80) is much greater than the other conÂstituents of the soil (mineral soil: 4, organic matter: 4, air: 1). Thus, when the amount of water changes in the soil, the probe will measure a change in capacitance (from the change in dielectric permittivity) that can be directly correlated with a change in water content. Circuitry inside the probe changes the capacitance measurement into a proportional millivolt output.
[edit] References
- Dane J.H., Topp G.C, co-editors 2002. "Methods of Soil Analysis Part 4-Physical Methods." Soil Science Society of America, Inc. Madison, Wisconsin.
- Czarnomski N.M., Moore G.W., Pypker T.G., Licata J. 2005. "Precision and accuracy of three alternative instruments for measuring soil water content in two forest soils of the Pacific Northwest". Canadian Journal of Forest Research 35, 8, pg. 1867.
