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

研制了一种由个人计算机控制的阻抗测量系统，用于实时测量土壤中的水分和电解质浓度。列。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，得到以下结论：采用接触式电极得到的结论是：土壤的电阻抗与含水量呈线性关系；土壤电导分别与土壤水分电导率和含水量呈线性关系；给出了理论评价函数，并通过实验验证了其有效性；悬浮度除以角频率的值是由含水量决定的，与土壤颗粒的大小无关。在土柱外表面设置非接触式电极，得到的结论是：在100kHz ~ 1MHz频率范围内测量到典型的介电色散现象；本研究中使用阻抗计的测量系统由于存在一些浮动元件，在几个MHz的频率范围内测量效果不佳；介电常数随含水量的增加呈增加趋势；随着土壤水电解质浓度的增加，介电常数的增加速率降低；建立了利用介电常数和电导率估算土壤水分和电解质浓度的评价函数，该函数对NaCl溶液在土壤柱中的非饱和运动具有较好的跟踪效果。从而证明了阻抗仪实时测量系统在土柱中溶液非饱和运动的有效性。

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.