What are the display methods of the soil moisture sensor?
The soil temperature and humidity recorder is composed of two sensors, namely a soil moisture sensor and a soil temperature sensor. It is precisely because multiple sensors can be connected that multiple parameters can be measured simultaneously. The multi-point soil temperature and humidity recorder is the most important instrument among soil detection instruments. Soil testing equipment is related to the growth of crops and is the basis of farmland operations. The moisture sensor is divided into two categories according to the display method: one is the direct display method, and the other is the secondary sensing method.
Direct display method: Direct display method can be divided into three types: one is the display type with suction negative pressure gauge (also called negative pressure tensiometer); the other is the display type with electric contact vacuum gauge, which is often used for alarm type moisture sensors; It is a U-tube mercury column display type. Among the three direct display methods, the U-shaped mercury column display has the highest accuracy, the most accurate reading, and the smallest error, which can be accurate to millibars. The disadvantage is that when the U-shaped tube ruptures in farmland use, mercury will pollute the farmland and cause environmental pollution. The choice of the three display modes is often selected according to the specific requirements of the user.
Secondary sensor display mode: The secondary sensor display type converts the pressure reading in the direct display sensor into moisture content. For example, the U-shaped tube mercury indicator part can be replaced with a piezoresistive sensor as the secondary sensor The digital soil moisture measurement device can be digitalized and directly display the value of the soil suction of the sensor. Secondary sensing can also be used to remotely measure soil water potential. For example, the soil moisture tensiometer (the sensor part) is buried in the soil depth required in the field, and the suction of soil water is transmitted through the penetration of the water film in the porous clay probe. , Make the moisture sensor generate negative pressure, this negative pressure is transmitted to the piezoresistive sensing current to the secondary sensor, giving an electric signal, which is transmitted to the remote temperature measuring instrument through the wire, and can be transmitted to the computer by the interface line to complete Remote measurement of soil water potential in the field. However, the negative pressure tensiometer can only measure the low suction range. When the suction is high, the clay head will be "pierced" by the air, so the soil water potential under high suction cannot be measured.
The sensor method for measuring soil moisture has the advantages of field in-situ measurement, rapid direct reading, no damage to soil structure, low price, no radioactive materials, safety and reliability, and easy long-term observation and accumulation of field water potential data. In particular, the secondary sensor has the advantages of digitization and can be connected with a computer interface to enable automatic monitoring of soil moisture measurement. This modern measurement method has become a new trend in the research of soil moisture measurement methods.
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