基于数字示波器的车载式土壤电导率检测系统研究

Vehicle Mounted Soil Conductivity Detection System Based on Digital Oscilloscope

在电流电压四端法原理基础上,采用信号发生器替代恒流源作为激励源来提供振幅更大、稳定性更高的正弦信号,以数字示波器替代电压源进行反馈信号检测从而解决电压有效值转换和AD转换频率较慢的问题,改进设计开发了一款基于数字示波器的土壤电导率检测系统。农田现场车载式测量实验分为稳定性检测和定点测量两部分。稳定性实验测试下该检测系统能够稳定读取相关数据。农田定点测量实验结合土壤样本采集和实验室实验,得出每个定点测量点土壤电导率测量值和土壤电导率实验室真值(R2=0.7531)。根据实验中拖拉机牵引犁盘抖动导致电极与待测土壤之间形成的两种测量接触面的情况,分析并消除了实验中拖拉机抖动现象对数据结果的影响后,土壤电导率实测数据与实验数据之间的决定系数R2提高到0.8552~0.9066,表明设备能够在排除测量方式等外界因素影响下,测量精度达到较高水平。实验数据对比结果显示,基于数字示波器的车载式土壤电导率仪能够在农田现场进行稳定测量,并且具有较好的性能和准确度。

Generally,there are two methods to detect soil electrical conductivity,which are contact and non-contact.Among them,the development of contact soil conductivity meter is generally based on the principle of currentvoltage four-terminal method,using constant current source as excitation source and voltmeter as feedback signal detection equipment.Based on the principle of current voltage four terminal method,the signal generator instead of constant current source was used as excitation source to provide sine signal with larger amplitude and higher stability,and the digital oscilloscope was used to replace voltage source for feedback signal detection,so as to solve the problem of slow frequency of voltage RMS conversion and AD conversion.A soil conductivity detection system based on digital oscilloscope was developed.The field vehicular measurement experiment was divided into two parts:stability detection and fixed-point measurement.Under the stability test,the detection system can read the relevant data stably.Field fixed-point measurement experiment combined with soil sample collection and laboratory experiment,the measured value of soil conductivity and the true value of soil conductivity at each fixed point were obtained.Based on the field experiment data as the ordinate and the laboratory measurement as the abscissa,the data scatter diagram was drawn,and R2 was 0.7531.In order to further explore the problem of poor correlation of experimental data,according to the situation of two kinds of measurement contact surface between electrode and soil to be measured caused by tractor traction plow disc shaking in the experiment.After analyzing and eliminating the influence of tractor shaking phenomenon on the data results,the determination coefficient R2 between the measured soil conductivity data and the experimental data can be increased to 0.8552~0.9066,which indicated that the equipment can achieve a high level of measurement accuracy without the influence of external factors such as measurement methods.According to the comparison of experimental data,the results showed that the vehicle mounted soil conductivity meter based on digital oscilloscope can stably measure in farmland,and had good performance and accuracy.