Soil humidity sensor is mainly used to measure the relative water content of the soil. This makes it widely used in soil science, agricultural science, environmental science, horticulture, botany and biology and other scientific experiments, soil moisture monitoring and agricultural irrigation and forestry protection, such as water-saving agricultural irrigation, greenhouse, flowers and vegetables, grassland, pastures, soil rapid measurement, plant culture. The soil moisture sensor is important for soil moisture monitoring system.

Working principle of soil humidity sensor:

The working principle of the soil moisture sensor is simple.The fork probe with 2 exposed conductors, functions as a variohm like a potentiometer whose resistance varies based on the water content in the ground.

The more water from the soil means greater conductivity and is going to create a lower resistance; Less water from the soil signifies poor conductivity and will bring a greater resistance. The soil moisture detector generates an output voltage in line with the resistance, which by soil moisture monitoring we can know the humidity level.

Features of soil humidity sensor:

1. Compact design of sensor volume, easy to carry, simple installation, operation and maintenance;

2. Reasonable structure design, no embroidery steel probe to ensure the service life;

3. The exterior is sealed with epoxy resin pure colloid, good sealing, can be directly buried in the soil for use, and not corroded;

4. High measurement accuracy, reliable performance, to ensure normal work;

5. Quick response speed and high data transmission efficiency.

Types of soil humidity sensor:

1. Capacitive soil moisture sensor

The sensitive element of capacitive soil moisture sensor is humidity sensitive capacitor, and the main materials are generally metal oxides and high polymer. These materials have a strong adsorption capacity to water molecules, the amount of water adsorption changes with the change of environmental humidity. Because the water molecule has a larger electric dipole moment, the permittivity of the material changes after water absorption, and the capacitance value of the capacitor also changes. The humidity can be monitored by changing the capacitance value into an electrical signal.

2. Resistive soil moisture sensor

The sensitive element of the resistance type soil hygrometer is the humidity sensitive resistance, and its main materials are generally dielectric, semiconductor, porous ceramics, etc. These materials have strong adsorption on water, and the resistivity/conductivity will change with the change of humidity after the adsorption of water. In this way, the change of humidity can lead to the change of the resistance value of the humidity sensor, and the change of the resistance value can be converted into the required electrical signal.

3. Ion type soil moisture sensor

Ion-sensitive field effect transistor (ISFET) is a kind of semiconductor biosensor. ISFET can measure the ion concentration in the solution by contacting the ion buffer solution directly through different sensitive film materials on the gate. The ion-sensitive device consists of two parts: an ion-selective membrane (sensitive membrane) and a converter. The sensitive membrane is used to identify the type and concentration of ions, while the converter converts the information perceived by the sensitive membrane into electrical signals.

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