The measurement accuracy of soil moisture temperature measuring instruments is influenced by various factors such as the instrument's own performance, soil characteristics, operation and installation methods, and external environment. These factors may interfere with the sensing signal or change the measurement benchmark, ultimately leading to data deviation, as follows:
Performance factors of the instrument itself
Quality and aging of core components: Sensors are the core of measuring instruments. For example, if the electrode of a capacitive moisture sensor is made of inferior material, it is prone to rapid oxidation, changing the dielectric properties and causing moisture measurement deviation; The temperature sensing element with poor thermistor material is difficult to accurately capture small temperature changes. After long-term use, aging problems such as electrode oxidation and electronic component parameter drift can cause a decrease in sensor sensitivity and gradually accumulate errors. In addition, the insufficient accuracy of auxiliary components such as signal amplifiers and analog-to-digital converters in instruments can also lead to distortion during signal transmission and conversion, affecting the final measurement results.
Factory and calibration deviation: Qualified instruments need to undergo precise calibration in a standard environment before leaving the factory. If the manufacturer's calibration process is not standardized, there may be deviations in the initial "signal parameter" corresponding curve, which will directly affect the measurement accuracy. At the same time, slow drift may occur during the use of sensors. If users do not calibrate regularly according to the frequency of use, or if the standard solution used for calibration fails, the deviation will continue to expand. For example, for devices that have not been calibrated for a long time, the humidity measurement error may increase from ± 2% to over 5%.
Soil self characteristic factors
Soil texture and uniformity: Different soil textures have different effects on measurement. The high cohesiveness of clay makes it easy for soil particles to adhere to the probe, hindering water and heat conduction; The large pores in sandy soil can cause gaps between the probe and the soil, leading to unstable sensing signals. Moreover, if the soil is mixed with a large amount of stones, plant roots, and other debris, it will prevent the probe from fully contacting the soil, disrupt the uniformity of the measurement, and cause local data distortion.
Soil salinity and chemical properties: When the salinity content is high in soils such as saline alkali land, it can interfere with the electric field distribution of capacitive sensors, resulting in higher moisture measurement values; The high or low acidity of soil can corrode the metal probe of the sensor, change its conductivity, not only affect the current measurement accuracy, but also accelerate component damage, further amplifying subsequent measurement errors. In addition, immature organic matter in the soil can alter the local temperature and humidity environment, and also cause measurement data to deviate from the true values.
Factors related to operation and installation standards
Improper installation method: If the probe is not inserted vertically into the soil or the insertion depth is insufficient during installation, it will result in insufficient contact area with the soil; Inserting probes with brute force in hard soil may also cause bending and damage to the probes, resulting in poor transmission of temperature and humidity. If the installation location is selected near the fertilizer pile, the edge of the field, or other special areas, the temperature and humidity in these areas are not representative and will directly lead to abnormal measurement data.
Improper sampling and use: Soil has spatial variability, and if only a single point measurement represents the entire area, it may result in biased results due to local soil differences. In addition, measuring immediately after rain may interfere with the true soil moisture data due to excessive surface moisture in the soil; If the probe is not cleaned in a timely manner after use, soil residues and salt crystals will adhere to the surface, indirectly changing the sensing characteristics of the probe and affecting the accuracy of the next measurement.
External environmental interference factors
Extreme temperature, humidity, and lighting: Extreme high temperatures can accelerate the aging of electronic components in instruments, while low temperatures may lead to unstable battery power supply, both of which can affect the response speed of sensors; When the environmental humidity is too high, the internal circuit of the instrument is prone to moisture corrosion, and even short circuits, which can damage signal transmission. Long term exposure to strong light can cause aging of the instrument casing and probe materials, while also altering the local microenvironment temperature and interfering with the accuracy of temperature measurement.
Vibration and electromagnetic interference: If the measuring instrument is installed near vibration sources such as water pumps and agricultural machinery, continuous vibration can cause the probe to loosen in contact with the soil and may also damage the internal structure of the instrument. The electromagnetic interference generated by transformers, motors and other equipment in industrial areas can affect the electronic signal processing module of instruments, resulting in temperature and humidity data readings jumping and distortion, especially for wireless transmission type measuring instruments.