Background:

Soil moisture is the source of plant survival. Soil moisture refers to the moisture content of soil. Soil moisture content directly affects the growth quality and speed of crops. In farming, crops themselves cannot directly obtain inorganic elements from the soil. Water in the soil acts as a solvent for dissolving these inorganic elements. Crops absorb soil moisture through their roots, obtaining nutrients and promoting growth. Therefore, precipitation or irrigation must be converted to soil. Water can be absorbed by plants. In the process of crop growth and development, different varieties have different requirements for soil temperature, water content and salinity. There are many methods to monitor soil moisture, soil temperature and humidity detector.

How soil moisture sensor works?

The most commonly used soil moisture sensors on the market are the tdr soil moisture sensor and fdr soil moisture sensor.

FDR soil moisture sensor working principle
FDR refers to frequency domain reflection, which uses the principle of electromagnetic pulse. The apparent dielectric constant (ε) of the soil is measured according to the frequency of electromagnetic waves propagating in the medium to obtain the soil volumetric water content (θv). The measurement principle, system installation, measurement method and application of FDR system in continuous dynamic monitoring of soil moisture are introduced, and the actual measurement results are corrected, which can be used as a reference for FDR correction.

TDR soil moisture sensor working principle
TDR refers to time domain reflectance, which is a common principle for quickly detecting soil moisture. The principle is that the waveform on a mismatched transmission line will reflect. The waveform at any point on the transmission line is the superposition of the original waveform and the reflected waveform. The response time of TDR principle equipment is about 10-20 seconds, which is suitable for mobile measurement and fixed-point monitoring.

What is the output of soil moisture sensor?

The probe is powered by a 4.5~30V DC power supply, and the output signal is a standard RS485modbus protocol.
The probe is powered by a 10~30V DC power supply, and the output signal can be 4-20ma, 0-5v, 0-10v.
The probe is powered by a DC 3.6V lithium battery and can output wirelessly, such as lora output.

How to calibrate a soil moisture sensor?

The most reliable way to calibrate any type of sensor is to compare it with a known good-performance instrument under actual humidity conditions. The relative humidity in the range of 50 to 90% is usually found between noon and midnight in summer, and another Methods, such as continuous water spraying in a civil bathroom, can be used in the high-mix range, and the relative humidity below 50% can sometimes be obtained in a central heating chamber, or it can be artificially manufactured indoors with an electric heater. The relative humidity in the room is usually 60% at 20°C. When the temperature is increased to 32°C, the relative humidity can be reduced to 30%. The best instruments for humidity reference are psychrometers and dew point meters. The dew point meter has an accurate calibrated thermometer, which is as accurate as the air temperature measurement, so it will give a reliable humidity value.

Which soil moisture sensor is best?

At present, there are many soil moisture measurement methods on the market, 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. The fdr soil moisture sensor and tdr soil moisture sensor are the two most widely used soil sensors with the best accuracy.

What does a soil sensor measure?

The soil moisture sensor measures or estimates the amount of water in the soil. According to the relative humidity of the soil, we can know the degree of soil moisture and how much water can be retained, which has reference value in irrigation. Soil moisture affects the field climate, soil aeration and nutrient decomposition, and is one of the important conditions for soil microbial activity and crop growth and development. These sensors can be handheld soil moisture sensor, electronic soil moisture sensor, digital soil sensor, or wireless smart soil sensor. The fixed soil moisture sensor is installed at the measuring point for long-term monitoring, while the portable soil moisture sensor can be moved at will to measure soil moisture in multiple locations.

How to make soil moisture sensor last longer

1. Vertical insertion of the sensor: Insert the sensor 90 degrees vertically into the soil to be tested. Do not shake the sensor when inserting it to prevent the sensor probe from being bent and damaging the probe.

2. Horizontal insertion of multiple sensors: Insert the sensors into the soil to be tested in parallel. This method is used for multi-layer soil moisture detection. Do not shake the sensor when inserting it to prevent the sensor probe from being bent and damaging the steel needle.

3. When you feel that there are lumps or foreign objects in the tested soil, please reselect the location of the tested soil, or remove the lumps in the current soil, and then continue testing.

4. When storing the soil sensor, wipe the three stainless steel needles clean with dry paper towels, cover them with foam, and store them in a dry environment at 0-60°C.

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