基于交流阻抗法的豆浆电特性检测

为实现豆浆品质快速检测和通电加热电源频率的优化，该文利用精密阻抗分析仪和DJS-10电导电极通过50 mV的激励电压在20 Hz～12 MHz频率范围内测量了不同温度（30～85℃）和不同固形物含量（1.01%～9.58%）的豆浆的交流阻抗。试验结果表明，豆浆阻抗模值与阻抗相位角随测量频率变化具有明显规律。豆浆的阻抗特性与温度以及固形物含量关系显著，且阻抗Nyquist 图存在明显差异。在全频段，豆浆阻抗模值随着温度和固形物含量的升高而减小；在低频段，豆浆阻抗相位角随温度以及固形物含量的升高而增大；在高频段，豆浆阻抗相位角随温度以及固形物含量的升高而减小。同时，研究提出了豆浆的电阻R、电容C、恒相位元件CPE（constant phase element）三元件等效电路模型，并用ZSimpWin软件进行拟合得到了试验条件下豆浆的等效电路元件参数。基于豆浆阻抗随频率变化规律及豆浆等效电路模型分析得出，豆浆通电加热电源的频率应在300 Hz～300 kHz范围内。豆浆的等效电阻R与温度以及固形物含量之间具有良好的负指数关系。CPE参数Q值随温度的升高而降低，当固形物含量超过3.5%后，Q值随固形物含量的升高迅速增加。CPE参数n值随温度的升高而升高，但在本研究中的固形物含量范围内n值并未随固形物含量的改变发生明显变化。本研究为豆浆通电加热电源的频率选择提供了参考依据，同时为基于豆浆电特性分析实现豆浆品质的快速检测奠定基础。

Detection of electrical properties of soybean milk based on AC impedance method

Abstract: In order to rapidly detect soybean milk quality and to optimize the frequency of power for ohmic heating device, the electrical impedance characteristics of soybean milk with different solid contents (ranging from 1.01% to 9.58%) at different temperatures (ranging from 30 ?C to 85 ?C with 5 ?C interval) were measured with an impedance analyzer at a frequency ranging from 20 Hz to 12 MHz. The impedance analyzer equipped with a commercial conductivity electrode (DJS-10) was operated at a measurement voltage of 50 mV. The temperature of the soybean milk contained in a jacket beaker was controlled with water flowing through the jacket at a constant temperature. The results showed that the impedance amplitude of the soybean milk decreased with the increase in frequency at a low frequency (f<300 Hz), and the impedance amplitude of the soybean milk did not change in the middle-frequency range (300 Hz 300 kHz). The impedance phase angle decreased with the increase in frequency at the low frequency range, and it tended to be zero in the middle-frequency range, while it showed the trend of increase in the high frequencies range. The results showed that the electrical impedance of soybean milk was significantly influenced by the temperature and solid content of soybean milk. There were clear distinctions among the Nyquist plot of electrical impedance for soybean milk with different solid contents at different temperatures. The electrical impedance amplitude of the soybean milk decreased with the increase in temperature and solid content in full frequency range. The impedance phase angle of the soybean milk increased with the increase in temperature and solid content in the low frequency range, while it showed the trend of decrease in the high frequency range. An equivalent electrical circuit of soybean milk which consisted of a resistor a capacitor and a constant phase element (CPE) was built for simulating the impedance data acquired during experiments. The electrical parameters of the equivalent electrical circuit were acquired with the ZSimpWin software. By analyzing the change in the impedance of the soybean milk with the frequency, combining with the equivalent circuit model, it was concluded that the frequency of the power for ohmic heating should be in the range from 300 Hz to 300 kHz. The experimental results also showed that the equivalent resistance (R) of soybean milk decreased with the increase in the temperature and the solids content, respectively. By the regression analysis on the data, it was found that the relationship between the equivalent resistance (R) and the temperature could be described by a negative exponential function (the coefficient of determination R2 was 0.996 at the solid content of 9.58%, P<0.01), the relationship between the equivalent resistance (R) and the solid content could be also described by a negative exponential function (the coefficient of determination R2 was 0.992 at 40 ?C, P<0.01). The value of Q (one of the parameters for describing the CPE) decreased with the increase in temperature; however, if the solid content of soybean milk was more than 3.5%, the value of Q increased sharply. The value of n (the other parameter for describing the CPE) increased with the increase in temperature, but it did not changed significantly with the solid content (ranged from 1.01% to 9.58%). The results in this research should be taken as a reference for selecting the frequency of the power for designing an ohmic heating system. In addition, the results also founded a method for detecting rapidly soybean milk quality on the analysis of electric parameters of soybean milk.