Several sources of error in soil moisture determination methods
Moisture is an important condition for plant development and growth. The study of soil moisture measurement by soil moisture detector is of great significance for accelerating scientific planting. If it is combined with temperature, light intensity, acidity, salt and other measurements, it can be connected with a computer to analyze and study the optimal growth of plants, and create favorable conditions for the development of agroforestry. In order to meet the needs of customers, our company has added the function of testing temperature on the basis of the original products. The instrument is called soil moisture temperature tester, and other functions are exactly the same.
Soil moisture measurement is a low moisture measurement, generally using conductivity. The method has the advantages of simple structure, convenient operation and low cost. The whole working process is: firstly, the oscillator generates a stable sinusoidal signal, and the output voltage of the amplifier reflects the change of soil water content through the equivalent resistance of the soil inserted between the probes in the soil, and the precision rectification circuit and filter Then, the MCU performs sampling, data processing, etc., and finally shows the soil water content.
The soil is a porous substance, and water exists in the soil pores in one or more of three states of solid, liquid, and gas. The soil state is relatively stable, and its electrical resistivity is an electrical parameter reflecting the soil water content. The soil water content is different from the natural solubility of various minerals, and its electrical resistivity is also different.
When inserting a probe into the soil, there are many factors that affect the measurement of soil moisture. The main factors that cause measurement errors are:
1. During the measurement process, the AC voltage output requirement of the oscillating circuit is constant, but there is still a certain change; at the same time, the soil has a certain capacitance, which will bring certain errors in the actual measurement.
2. When the probe is inserted into the soil, the sloshing, the degree of soil looseness, and the temperature will have an insurmountable effect on the measurement results.
3. There is polarization of the surface of the probe during the measurement process, which causes corrosion on the surface of the probe. Although the probe is powered by AC, there is still corrosion behavior on the surface of the probe, which affects the change of electrical parameters. In addition, the probe is required to have no corners or convex portions, so the probe is cylindrical.
4. The drying method is used for calibration, and the soil diffusion is required to be uniform to reduce the error caused by the calibration.
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