水培营养液硝态氮浓度在线标测系统研究

Construction and Verification of On-line Calibrating and Measuring System about Nitrate N in Hydroponic Nutrient Solution

针对目前氮素浓度检测技术中电极标定过程与离子检测过程分离,难以实现在线检测的问题,设计了一套基于双传感器冗余控制的水培营养液硝态氮浓度在线标测系统。系统的标定过程为利用丝杠滑块线性导轨完成电极清洗和标准液电压获取,并采用最小二乘法,辨识所采集电压与离子浓度对数之间标准曲线的参数。系统的检测过程为基于最大误差原理,采用双传感器冗余控制方法进行数据融合和标定决策,最终实现硝态氮浓度的连续在线检测。验证试验结果表明:双传感器冗余控制方法可靠,在线检测值与离子色谱法获得的实验室检测值平均相对误差仅为5.64%,平均绝对误差只有1.172×10-5,二者呈现极显著线性相关关系(P<0.01)。综合分析得出,该系统能够实现营养液连续消耗情况下硝态氮浓度的在线检测,其结果与实验室检测值具有较好的一致性,解决了人工标定电极费时、费工的问题,提高了检测效率,为营养液的精细化管理提供了新的技术手段。

Efficiently obtaining the concentration of nitrate N（NO_3^--N） in hydroponic nutrient solution is essential for crop growth. However,it is difficult to realize on-line detection due to the separation of electrode calibration and ion detection. In order to obtain the concentration of NO_3^-N promptly,conveniently and accurately,an on-line calibrating and measuring system was established based on dualsensor redundancy control method and nitrate ion-selective electrode（ISE）. When calibrating,screw nuts were developed for driving ISEs to move in two degrees of freedom,for the purpose of rinsing electrodes and getting standard voltages. Additionally,unknown parameters of the linear function between collected voltages and logarithms of the ion concentrations were recognized under the least squares fitting method. When measuring,a dual-sensor redundancy control method was applied to carry out periodically calibrating and rinsing,as well as on-line measurement based on the principle of maximum error. To test and verify the accuracy of this system,a no-load test and a production test were carried out. The former was compared the on-line detection concentrations with the actual values of NO_3^-N in the 14 single-ion（KNO3） solutions,and the latter continuously monitored the concentrations of NO_3^-N for 12 d in the process of lettuce production. The results showed that the dual-censor redundancy control method was reliable. The on-line detection measured by this system and the laboratory detection measured by ion chromatography showed an extremely significant linear positive correlation（P〈 0. 01）,and the mean of average relative error was merely 5. 64%,and the mean of average absolute error was 1. 172 × 10-5.Therefore,the system could realize the on-line detection of NO_3^-N under the continual consumption of nutrient solution,which not only had strongly relation to those determined by laboratory instrument,but also solved the problems of time-consuming and labor-intensive about manual calibration.