The soil is a mixture of dry earth, moisture and air. Since the dielectric constant of water is several tens of times higher than that of dry soil, soil moisture directly affects the dielectric constant of the soil. Under high frequency electric field, the impedance of soil changes with the change of soil moisture content. By detecting the change of impedance, the soil moisture content can be detected. The schematic diagram of the principle of the electric field method for measuring the moisture content in the soil moisture recorder is shown in Figure 1.
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Description
LDG Ribbon Vacuum Drying Machine is a
high-efficiency vertical type drying equipment which integrates drying,
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to five times of the same specification Double Cone Vacuum Dryer.
This Ribbon Vacuum Dryer Machine is used
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Features
of Ribbon Vacuum Dryer Machine
1. The working process of LDG
drying machine uses intermittent operation, after the wet materials enter into
the stock bin, through the wall jacket to heat and dry the materials. Transmission
shaft heating is also available, which can heat more sufficiently.
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machine adopts small angle taper type tube structure, which makes quick
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Main
Components
LDG ribbon vacuum drying machine consists
of motor, reducer, rack, mechanical seal, filer, helical ribbon mixer, conical
cylinder with jacket heating and discharging valve.
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In Fig. 1, the soil between the probes is equivalent to the impedance that changes with the moisture content under the action of high-frequency signals. The greater the moisture content, the smaller the impedance measured by the soil moisture recorder, which is equivalent to the signal source. load. When the load is not negligible with respect to the signal source internal resistance, the amplitude of the signal source output will change. The soil moisture recorder can obtain the soil moisture content by measuring the amplitude change of the signal source.
When different frequency sources act on the same soil, the soil exhibits different impedance characteristics. The impedance characteristics of the soil are given. When the frequency is lower than 20 MHz, the soil impedance is large, the moisture content has little effect on the soil impedance, and the sensitivity is very low. When the frequency is 280 MHz, the soil impedance is very small, and the moisture content is on the soil. Impedance has a great influence. Using the Agilent high-frequency signal generator (E8257C), sinusoidal signals with a frequency of 10 to 120 MHz (a step increase of 10 MHz) and a no-load voltage amplitude of 3.3 V were used to determine the voltage output values ​​of the same soil under different moisture contents. . Comparing the linear relationship between voltage measurement and moisture content and stability, and taking into account the difficulty and power consumption of the high-frequency generating circuit, the frequency is selected to be 50 MHz, the amplitude is 3.3 V, and the internal resistance is the same as the impedance of the soil. An order of magnitude sine wave is used as a signal source.
Since the soil moisture recorder only considers the change of soil impedance with water content, and ignores its inductive reactance and capacitive reactance, it does not need to detect the change of the phase of the signal source output, only the change of the signal source amplitude is detected. The detected voltage signal is rectified and filtered, and the A/D converter is used to detect the signal output.
The above is the principle of applying soil electric field knowledge to measure soil moisture in a soil moisture recorder.