How to choose a soil moisture sensor
Soil wetness sensor
The soil water sensor is a kind of soil sensor. By measuring changes in soil properties related to water content, the soil water content can be indirectly obtained. Common changes with water content. And easily measured soil properties include dielectric constant, thermal conductivity and neutron flux density.
Dielectric constant sensor is a common soil moisture sensor on the market. It uses different techniques for measurement. Including: time domain reflection method, time domain transmittance, frequency domain reflection method. Charging capacitor time method, transmission line oscillation method, coaxial impedance medium reflection method.
Dielectric constant
Permittivity can be understood as storing electrical energy. When the sensor measures, an electric field is excited in the soil, because water molecules are polar. The unbound water molecules in the soil will rotate to align with the electric field lines.The rotation of unbound water molecules requires energy. Energy is stored in neatly arranged water molecules in the form of potential energy. The more water there is in the soil, the more energy it can store and the higher the volume permittivity of the soil.
The soil water sensor is designed as an electrical signal that changes with the dielectric constant. Some of these soil detector measure the dielectric constant (the moisture content also changes with it) and convert it to soil moisture content. The electrical signal output of other soil detector is converted into soil volumetric water content in only one step.
Summarize
No matter which method is used, the moisture in the soil will affect the volume permittivity. But no matter which technology is used, the principle is the same: the volumetric dielectric constant of the soil changes with the volumetric water content. The volume dielectric constant will affect the electrical output of the sensor. This is important when comparing sensor accuracy specifications.
