温室营养液循环检测系统中离子选择电极的数学建模与测量

针对目前设施农业中使用离子选择电极对营养液养分进行在线测量所存在的长时间测量和测量准确性问题,提出使用基于最小二乘法的“逐步拟合法”拟合钾、钙、硝态氮等离子选择电极模型,建立被测溶液浓度,电极测量电压和被测溶液温度的三维数学模型。并由此设计出营养液各养分含量的在线测量方法。以钾离子选择电极为例介绍了离子选择电极的试验测量方法、建模原理和过程。通过建模得到了钾离子选择电极的一个以温度的一次函数作为常数项和测量电压自变量的系数项、溶液浓度为应变量的函数模型。大量的实验结果表明：所建立的离子选择电极模型准确,可用于在线检测,提出的方法在工程上简洁实用,具有广泛的应用价值。

Modeling and measurement of ion-selective electrode of nutrient solution measuring system in greenhouse

For solving the problem of on-line measurement of the contents of nutrient solutions in greenhouse agriculture, a new method fitting the models of K⁺, Ca²⁺, NO^-₃ ion-selective electrodes (ISE) named "step-by-step fitting" which is based on the theory of LS was put forward in this paper. The new method establishes a 3-dimensional model of the ion concentrations, the temperatures of the solutions and the voltage outputs of ISE. Taking the K⁺ ISE as an example, the measurement, the theory and application of ISE modeling was introduced in the paper. Finally a function that had the ISE voltage output as its independent variable, the temperature's linear functions as its coefficients, and the ISE concentration as its attributive variable was constructed. A lot of application results demonstrated that the model constructed in the paper was precise, and the new method will be widely used in online measurement in a concise way.