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Working principle of soil moisture sensor

by:Rika Sensors     2021-11-19
Working principle of soil moisture sensor
Soil moisture sensor, also known as: soil moisture sensor, soil moisture sensor, soil moisture sensor, is mainly used to measure soil volumetric water content. For soil moisture monitoring and agricultural irrigation and forestry protection, the commonly used soil moisture sensors are FDR type and TDR type, that is, frequency domain type and time domain type. The FDR type is currently more popular. The FDR frequency domain reflectometer is an instrument used to measure soil moisture. It has the advantages of simplicity and safety, fast and accurate, continuous fixed point, automation, wide range, and less calibration.

At present, there are many soil moisture measurement methods at home and abroad, and there are different soil moisture sensors. For example: Time Domain Reflectometry (TDR), Plaster Method, Infrared Remote Sensing Method, Frequency Domain Reflectance Method/Frequency Domain Method (FDR/FD Method), Titration Method, Capacitance Method, Resistance Method, Microwave Method, Neutron Method, Karl Fischer Method, Y-ray method and nuclear magnetic resonance method. Below we introduce the working principle of each sensor.

1. TDR method moisture sensor:

The TDR method is a soil moisture measurement method developed in the 1980s. The Chinese is a time domain reflectometer. This method is widely used in foreign countries, and it has just begun to be introduced in China, and all departments have paid great attention to it. TDR is a system similar to a radar system, with strong independence, and its results are basically independent of soil type, density, and temperature. And it is also very important that TDR can measure soil moisture under icy conditions, which is unmatched by other methods. In addition, TDR can monitor the soil water and salt content at the same time, and there is almost no difference between the results of the two measurements. The degree of this measurement method is evident.

Second, FDR and FD method moisture sensor:

Because the TDR method equipment is expensive, in the late 1980s, many companies (such as AquaSPY, Sentek.Delta-T, Decagon) began to use simpler than TDR Methods to measure the dielectric constant of the soil. The FDR and FD methods are not only cheaper than TDR, but also have a shorter measurement time. After a specific soil calibration, the measurement accuracy is high, and the shape of the probe is not limited, and it can be measured at multiple depths at the same time. Data collection is easier to implement.

Three, resistance method moisture sensor:

The resistance method uses the resistance of gypsum, nylon, glass fiber, etc. and their moisture content. When these intermediates plus electrodes are placed in moist soil, and then after a period of time, the water content of these things reaches equilibrium. Due to the relationship between resistance and moisture content, we have previously calibrated a certain correspondence between resistance and percentage, and then we can use these components to obtain moisture readings within the suction range of 1 to 15 atmospheres.

Four, neutron scattering (neutron scattering) moisture sensor:

The neutron method is suitable for measuring soil moisture in the field. It is based on the principle that hydrogen drastically reduces the speed of fast neutrons and scatters them away. Now there are neutron moisture meters for measuring soil moisture on the market. The neutron moisture meter has many advantages, but it has considerable restrictions on organic soil, and it is not suitable for measuring the soil moisture content of 0-15 cm.

V. Y-ray moisture sensor:

Similar to the neutron instrument, the ray transmission method uses the radioactive source 137Cs to emit a line, and the probe receives the energy of the ray through the soil, and the soil moisture The content is converted.

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