脉宽调制式电子分析天平的漂移补偿方法研究

Study on drift compensation method of PWM electronic analytical balance

温漂和时漂对脉宽调制式电子分析天平示值影响较大且难以区分,分析了永磁体剩磁、动圈长度、恒流源采样电阻、电子元件参数等温漂和时漂影响机理,考虑电磁力平衡传感器各特征位置温度变化及内外温度梯度影响,建立了温漂与温度变化的二次多项式、与温度梯度的近似线性关系以及时漂与时间的指数关系,通过叠加得到示值漂移非线性混合补偿模型,并设计了一种能够同时辨识温漂和时漂模型参数的空载和满载组合漂移实验和数据处理方法,通过大量非均匀温度变化实验得到模型参数,利用该模型对量程220 g、分辨力0.1 mg的电子分析天平进行补偿验证。结果表明,补偿后的天平加载220 g并保持30 min后的示值漂移小于1 mg,零点示值漂移小于0.5 mg,满足国家标准《JJG1036-2008电子天平检定规程》规定的Ⅰ级天平对温漂和时漂性能指标要求。

Temperature drift and time-varying drift have great effects on PWM electronic analytical balance indication and can not be easily distinguished. In this paper, the temperature and time drift mechanism is analyzed, which includes permanent magnet residual magnetism, movable coil length, constant current source sampling resistor and electronic component parameters. The impact of multi-point temperature changes and temperature gradient of the electromagnetic force balance sensor are considered; the quadratic polynomial of temperature drift vs. temperature change, the approximate linear relation between temperature drift and temperature gradient, and the exponential relation between time drift and time are established; and a nonlinear hybrid compensation model of the balance indication drift is obtained through superimposition. Drift experiment and data processing method were designed that could identify the parameters of the model simultaneously; the model parameters were obtained through various uneven temperature changing experiments. This model was used to conduct the compensation verification on the electronic analytical balance with capacity of 220 g and resolution of 0.1 mg, experiment results show that when the balance is loaded with 220 g and after operating for 30 min, its full-drift is under 1mg, zero-drift is under 0.5mg, which well satisfies the temperature and time drift performance requirement of 1st class electronic balance defined in the Chinese National Standard, ＂JJG1036-2008 Verification Regulation for Electronic Balance＂.