Development of a real time measurement system for tracing water and solute movement in an unsaturated soil column

研制了一种由微机控制的阻抗测量系统，用于土壤含水量和电解质浓度的真实的实时测量。柱在恒温条件下研究了该系统的效率。采用接触式电极和非接触式电极对土壤进行了研究，得出以下结论：接触式电极的土壤电导率与土壤含水量呈线性关系，土壤电导率与土壤水电导率和土壤含水量呈线性关系，给出了理论评价函数，并通过实验验证了其有效性;在土柱外表面布置非接触式电极，得到的结论是：在100 kHz ~ 1 MHz频率范围内，土柱内存在典型的介电频散现象;本研究中使用阻抗计的测量系统由于一些浮动组件而不足以在几MHz的频率上进行测量;介电常数随土壤含水量的增加呈增加趋势，随土壤水电解质浓度的增加，介电常数的增加速率减小;利用介电常数和电导率建立了估算土壤水含水量和电解质浓度的评价函数，表明该评价函数能有效地跟踪NaCl溶液的非饱和运动结果表明，采用阻抗计的真实的时间测量系统测量溶液在土柱中的非饱和运动是有效的。

An impedance measurement system controlled by personal computer was developed for a real time measurement of water content and the concentration of electrolyte in a soil. column. The efficiency of this system is studied under a constant temperature condition. Contact-type electrodes and non-contact-type electrodes were used and the following conclusions were obtained.Conclusions obtained by using contact-type electrodes were : suseptance of soil had a linear relationship with water content; conductance of soil had linear relationships with electric conductivity of soil water and water content respectively; the theoretical evaluation function was shown and its efficiency was proved to be right by some experiments; the value of suseptance divided by an angular frequency was determined by water content with no relation to the size of soil particles.Conclusions obtained by using non-contact-type electrodes arranged on an outer surface of a soil column were : typical dielectric dispersion phenomenon was measured at frequencies between 100kHz and 1MHz;the measurement system of this study using impedance meters were not good enough for the measurement over the frequencies of several MHz due to some floating components; dielectric constants showed an increasing tendency with relation to the increase of water content; increasing rate of dielectric constants decreased when the concentration of electrolyte of soil water increased; an evaluation function for estimating water content and the concentration of electrolyte of soil water was developed using dielectric constants and electric conductance and it showed its efficiency for tracing unsaturated movement of NaCl solution through a soil column.Consequently, the efficiency of the real time measurement system using impedance meters for measuring the unsaturated movement of solution through a soil column was shown.