该文设计了一种无线多点土壤电阻率测量系统，该系统包括一个主机和多个从机，根据电流-电压四端法原理自制了土壤电阻率测量传感器，以减小对土壤溶质移动的干扰，采用主从式通信建立测量平台，从机完成土壤电阻率数据的采集、发送功能，从机个数可以根据测量点的要求进行扩展，主机完成土壤电阻率数据接收、处理、显示及存储功能，主机和从机无线通信，采用nRF24L01无线模块，构成了“一对多”的通信网络。系统有效地解决多点土壤电阻率实时测量的一致性问题，试验结果表明系统具有良好的稳定性和实用性，室外无线有效传输距离可以达到95 m，室内达到75 m，土壤电阻率与含盐量及加水量呈良好的线性关系（R2=0.9991），与其他测试仪测量的曲线基本吻合，相对误差在1%以内，具备较好的测量精度。%This paper describes the design of a wireless multi-point soil resistivity measurement system. The system is composed of many slaves and a host. According to "the principle of current - voltage four terminal methods,"this paper presents a sensor made in our laborator. It included an A/D conversion chip MCU, wireless communication circuit, the sine wave generating circuit, AC constant current source circuit, sensor electrode, differential circuit, conversion circuit, amplifier circuit, and digital potentiometer effective value. It can reduce the interference of soil solute movement. The system was established by measuring a platform of master-slave communication. The slave completes the soil resistivity data acquisition and transmission. A number of slaves can be extended according to the requirements of the measuring point. The host comprised a single chip computer, a liquid crystal display circuit, external data storage circuit, wireless communication circuit. And the key circuit completes the soil resistivity data receiving, processing, display, and storage function. Wireless communication circuit adopts nRF24L01 wireless module, and can constitute a"one-to-many"communication network. In order to stabilize amplitude alternating test design of the constant current source, the simulation test of soil impedance changes using a variable resistance, used for the test of stability constant current source, the relative error of the elongation is 2.63%, and it has good stability. Outdoor wireless transmission distance can reach 95m, indoor reached 75m. The system effectively solves the multi-point soil resistivity measurement consistency problem. There was a good linear relationship between salt content of soil and soil resistivity measured systematically, the higher is the salinity, the smaller is the soil resistivity measured. There was a good linear relationship between the soil resistivity measured systematically and the amount of water, the larger is the add water amount, the smaller is soil resistivity measured. The design of the system is novel, is simple to operate, with good portability, and soil resistivity data to detect intelligent automated multiple locations can be moved at any time. At the same time, the construction is convenient, has a broad application .prospect in production, and can be widely popularized.
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