CAJ | 학술논문

为实现肥液自动混合过程中氮素浓度的实时检测，设计了一个检测装置，该装置主要由硝酸根离子选择电极、电极信号调理电路、温度传感器、数据采集以及显示电路组成。在10-6～10-1 mol/L范围内配制了一系列标准浓度的NO3-溶液，对该检测装置进行了性能测试试验：1）以标准毫伏计 PHS-3CT 作为对比，测试了装置对电极响应电势的测量准确性，其相对误差最大为5.2%；2）在5～45℃范围内，分析了离子选择电极的温度变异性，结果表明电极响应电势随着待测溶液温度升高而呈线性变化，在此基础上采用最小二乘法的逐步拟合方法建立了温度参数模型，并对模型进行了验证，其测量误差最大为9.2%；3）采用固定干扰法分析了Cl-、SO42-、H2PO4-和HPO42-等4种干扰离子对装置测量结果的影响，结果表明Cl-引起的干扰最大，电极对Cl-的敏感性是NO3-的0.2%，因而肥液中少量的干扰离子对测量结果的影响不大。因此，该装置可满足工程上自动混肥过程中氮素浓度检测的应用要求。
위실현비액자동혼합과정중담소농도적실시검측，설계료일개검측장치，해장치주요유초산근리자선택전겁、전겁신호조리전로、온도전감기、수거채집이급현시전로조성。재10-6～10-1 mol/L범위내배제료일계렬표준농도적NO3-용액，대해검측장치진행료성능측시시험：1）이표준호복계 PHS-3CT 작위대비，측시료장치대전겁향응전세적측량준학성，기상대오차최대위5.2%；2）재5～45℃범위내，분석료리자선택전겁적온도변이성，결과표명전겁향응전세수착대측용액온도승고이정선성변화，재차기출상채용최소이승법적축보의합방법건립료온도삼수모형，병대모형진행료험증，기측량오차최대위9.2%；3）채용고정간우법분석료Cl-、SO42-、H2PO4-화HPO42-등4충간우리자대장치측량결과적영향，결과표명Cl-인기적간우최대，전겁대Cl-적민감성시NO3-적0.2%，인이비액중소량적간우리자대측량결과적영향불대。인차，해장치가만족공정상자동혼비과정중담소농도검측적응용요구。
For the realization of real-time detection of nitrogen concentration in the process of automatic mixed liquid fertilizer, a detection device was designed, which was mainly composed of a nitrate ion selective electrode, an electrode signal conditioning circuit, a temperature sensor, and a data acquisition and display circuit. There was a one-to-one correspondence between the response potential of a nitrate ion selective electrode and nitrate ion concentration. For this reason, the detection device could obtain the level of nitrate ion concentration by detecting the electrode’s response potential, and then the nitrogen concentration of liquid fertilizer had been acquired indirectly. Measuring accuracy for the electrode’s potential was a key influence factor of the device’s performance. A 1 mV error of the electrode’s potential led to a 4% concentration measuring error of monovalent ions. To evaluate the device’s measuring accuracy for an electrode’s potential, the electrode had been placed in a series of prepared potassium nitrate solutions whose NO3-concentration were 10-6, 5×10-6, 10-5, 5×10-5, 10-4, 5×10-4, 10-3, 5×10-3,10-2, 5×10-2, and 10-1mol/L respectively, and the response potential of the electrode was measured by the device and a standard millivoltmeter PHS-3CT which was used as the comparative reference respectively, and it was known from the test results that the device’s measuring result for the electrode’s potential in each NO3-concentration was closed to that of PHS-3CT, and its maximum and minimum relative error were 5.2% and 1.2% respectively. Meanwhile, the response potential of the electrode would produce a temperature drift when the temperature varied, which would result in a measuring error of ion concentration. For reducing the influence of temperature variation, the electrode’s temperature variability had been analyzed with 25℃ as a reference, by measuring its response potential in a series of prepared solutions with different NO3-concentrations in the range of 10-5-10-1 mol/L and different temperatures within the scope of 5-45℃. The results showed that the response potential of the electrode had a linear change with the temperature difference of the solution to be examined and the maximum variability rate of the potential was 8.8%. Based on the response potential of the electrode measured in a series of prepared solutions with different NO3-concentrations and different temperatures, a temperature parameter model had been established by using the method of the least squares fitting step by step. Verification experiments of the temperature parameter model had been carried out, by using three kinds of prepared potassium nitrate solutions whose NO3-concentration were 4×10-1, 4×10-2 and 4×10-3 mol·L-1 severally, and it turned out that the average relative measurement error and the maximum relative measurement error of the temperature parameter model were 4.49% and 9.2% separately. Furthermore, there may be some interfering ions (such as Cl-, SO42-, H2PO4- and HPO42-) in a mixed liquid fertilizer in addition to NO3-, and the nitrate ion selective electrode had cross sensitivity. It would allow the electrode’s response for interfering ions to come into being, which could bring about some impact on the device’s measuring results. In order to determine the degree of influence of the interfering ions for the device’s measuring results, the fixed interference method had been used to measure the electrode’s selectivity coefficient for Cl-, SO42-, H2PO4- , and HPO42- respectively. The results indicated that the selectivity coefficient for 4 interfering ions were 5.1×10-2, 1.0×10-4, 2.0×10-4, and 5.0×10-5 singly, and that the bigger the selectivity coefficient was, the greater the impact of interfering ions on the electrode; moreover, it was found from experiments that the effects of interfering ions on the electrode weakened gradually with the decrease of the interfering ions concentration, and the measuring error of the device caused by Cl- was 4% when Cl-: NO3- = 1:100, that was to say, a small amount of interfering ions in a liquid fertilizer could not constitute a significant effect for the measured results. From the above, the device developed could meet the application requirements of a nitrogen concentration test in the process of automatically mixed fertilizer in engineering.