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MAS-1 Soil Moisture Sensor

2. About the MAS-1

The MAS-1 measures the dielectric constant of the soil in

order to find its volumetric water content. Since the dielec-

tric constant of water is much higher than that of air or soil

minerals, the dielectric constant of the soil is a sensitive

measure of water content. The MAS-1 supplies a 70 MHz

oscillating wave to the sensor prongs that induces an electro-

magnetic field in the medium (soil) surrounding the sensor.

The charging and discharging of the sensor is controlled by

the dielectric of the surrounding soil.

A microprocessor on the MAS-1 measures the charging of

the sensor, and therefore the dielectric constant of the soil

which is related to the water content of the soil. The micro-

processor makes a dielectric measurement and updates the

transmitted current once per second. The transmitted 4-20

mA current can be converted to the water content of the soil

using a simple calibration function.

The MAS-1 was designed to be used with standard 4-20 mA

controllers and monitoring systems. It cannot be used with

Decagon logging systems. For more information about

using Decagon logging systems please contact Decagon's

customer support representatives.