Development And Research Of Temperature Self-compensated SWR Soil Moisture Sensor

Water is the basic nutrient that sustains all the life activities of plants.It is also one of the main factors that ensure the smooth progress of photosynthesis,respiration and other physiological processes.The soil supplies the required water to the plant,and when the soil moisture changes,it affects the life state of the plant.Accurate measurement of soil moisture is of great significance for the study of the mechanism of plant water deficit.In the long-term monitoring process of forest microenvironment and farmland moisture,the soil moisture sensor based on dielectric method is affected by the change of environmental temperature,which leads to the decrease of measurement accuracy and accuracy.Based on the above reasons,this paper carries out the following research work:1.The principle of platinum resistance temperature measurement and the measurement principle of soil dielectric properties were studied.The composition of the dielectric constant of unsaturated soil was analyzed,and the physical model of the equivalent circuit describing the dielectric properties was introduced.The hardware circuit of soil moisture sensor based on the principle of standing wave rate and the constant current source driving circuit and signal conditioning circuit of PT100 temperature sensor were built,and the system software design was completed.2.Comprehensive testing of the designed composite sensor,including hardware circuit test,debug simulation test,calibration experiment and comparison experiment of standard instrument.According to the calibration experiment results,the determination coefficients of the output voltage value of the composite sensor and the measured linear fitting are all greater than 0.99,indicating that the linear relationship between them is significant.The TDR sensor of IMKO of Germany was selected as the standard instrument for comparative experiments.The error of the SWR soil moisture sensor designed in this paper is within±2%,indicating that the performance of the two is equivalent.3.The temperature drift characteristics of the SWR soil moisture sensor are analyzed from two aspects:hardware composition and measurement principle.The volumetric water content of the soil sample is in the range of 7.46%to 30.30%,and the experimental temperature is 5? to 45?.The test results show that the error of soil volume moisture content measured by the sensor is-2.65%-2.22%,the maximum relative error is 29.76%,and the maximum mean square error is 2.211 9.4.This paper proposes a binary regression analysis based on the least squares principle for temperature compensation of sensors.The results showed that the error distribution of SWR sensor measurement results after this model compensation was-0.26%?0.69%,the maximum relative error was not more than 5.23%,the mean square error was reduced by an order of magnitude and the maximum mean square error was 0.157In summary,this paper designs a SWR soil moisture sensor with automatic temperature compensation function to quickly and accurately obtain soil moisture information,and provide basic data for agroforestry production,ecological protection,soil and water conservation and other fields.