Vaisala WMS302 Guide de l'utilisateur télécharger pdf (Page 46)

User's Guide ______________________________________________________________________

44 ___________________________________________________________________M210630EN-B

Soil Moisture Sensor

0406-050

Figure 31 Soil Moisture Sensor ECH2O-M3

The ECH2O-M3 probe is a low-cost sensor for measuring volumetric

water content of soil and other porous materials. It uses 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 constituents of the soil (mineral soil, 4;

organic matter, 4; air, 1). Thus, when the amount of water changes in

the soil, the ECH2O-M3 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 ECH2O-

M3 probe changes the capacitance measurement into a proportional

millivolt output. The ECH20-M3 probe has a low sensitivity to salt and

temperature, and very low power consumption.

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Vaisala WMS302 Guide de l'utilisateur Page 46