一种多点土壤电导率实时监测系统的研制

为获取建立溶质运移模型所需的土壤溶质浓度参数,根据土壤溶液电导率与溶液浓度c的线性关系,应用电流电压四端法,研制出一种多点土壤电导率实时监测系统。该系统硬件部分自行设计的四针微型探头可减小对溶质运移的扰动,且可高密度分布在土壤中;连接8路电导率探头和1路温度探头的高精度数据采集器DAB能够实现8通道土壤电导率测量及温度辅助测量,并可通过485总线接口实现系统规模的扩展。采用VC开发的监测显示平台能够完成采集器参数设置,数据采集、显示与存储功能。通过对采集器通道和探头的标定,有效解决了多点土壤电导率实时监测的一致性问题。标定试验结果表明,数据采集器8通道电导测量值与标准电导的相关系数为0.999 5,表明通道标定后有效提高了其测量准确度,减小了各通道测量差异;通道标定后采集器各通道测量的标准溶液电导G与其电导率σ具有良好的线性关系,但不同电导率条件下探头的测量结果存在较为明显的偏差,说明探头制作过程引起的结构差异不可忽略,进而采用分段标定方法对每一个探头的结构常数进行标定。

Development of a multipoint real-time monitoring system for soil electrical conductivity

In order to obtain the concentration of soil solution that has a linear relationship with the soil electrical conductivity(EC) for solute transport modeling a multipoint EC measurement system using the principle of four-electrode measurement method to determine EC was developed.The system hardware,including special designed small 4-pin probes,data acquisition boards(DAB),and temperature sensors,was integrated to compensate the temperature effect on EC.The monitoring software developed by VC programming language was adopted for collecting,displaying and storing functions of EC with the system hardware together.The consistency of multipoint measurements was resolved by calibrating to channels and probes.A series of experiments was carried out to reduce the effects from channels of DAB and sensors.The correlative coefficient between the measured and standard conductance is(0.999?5,) which shows that the experiments for calibration are necessary.While,the measuring errors from probes shouldn't be ignored and the structural constants of each probe should be calibrated section by section.