基于拉格朗日抛物线插值的毛细管粘度仪液位检测方法

为提高毛细管粘度仪液位检测的实时性,减小凹形液面和采样间隔对检测结果精度的影响,提出了一种基于拉格朗日抛物线插值的毛细管粘度仪液位检测方法。采用光纤传感器作为液位检测元件,对采样得到的液位检测电压信号进行一阶差分处理;搜索一阶差分最小采样时刻,选取该采样时刻与其前后相邻2个采样时刻的电压一阶差分值作为插值点,进行拉格朗日抛物线插值;通过插值多项式对时间求导,确定计时点,实现液位流经2个计时点的自动检测。该方法与现有基于最小二乘线性拟合方法相比,计算量小,实时性好,受采样间隔影响小。实验表明该方法的运动粘度测定重复性小于0.1%。

A Liquid-level Detection Method for Capillary Viscometer Based on Lagrange Parabolic Interpolation

In order to improve the real-time performance of the liquid-level detection for capillary viscometer and diminish the impact of concave liquid-level and sampling interval on the accuracy of the detection, a liquid-level detection method based on Lagrange parabolic interpolation is proposed. Fiber optic sensors are used as liquid-level detection components. Firstly, the first order difference of the sampling data is figured out. Then Lagrange parabolic interpolation is operated on the sampling data’s first order difference of the sampling time with the least first order difference and its adjacent sampling time. Finally, the timing point is worked out with the time derivative of the interpolation polynomial and the automatic liquid-level detection at the two timing positions is accomplished. Compared with the existing method based on least squares linear fitting, the proposed method has better real-time performance for the less calculation and is less impacted by the sampling interval. Experiments show that the repetitiveness of kinematic viscosity measured with the method is less than 0.1%.