基于置信规则库推理的驻波液位仪误差补偿

Measuring Error Compensation of Standing Wave Based Liquid Lever Meter Using Belief Rule Base Reasoning

在基于声波共振原理的液位测量方法中,其测量误差通常是根据不同的液位测量高度进行分段补偿的,显然这种补偿不够精确.针对此问题,提出一种基于置信规则库推理(BRB)的测量误差补偿方法.由于不同液位高度下的测量误差大小与合成声波中的驻波个数、相邻驻波频率差的均值以及标准差等参数有密切关系,所以利用置信规则模型建立这些输入参数与输出补偿量之间的非线性关系.当在某一液位高度下获取输入参数值后,激活置信规则库中相对应的规则,运用证据推理(ER)算法融合被激活规则后项中的置信结构,在融合的结果中得出相应液位高度对应的误差补偿量,从而得到精确的测量结果.通过液位测量实验及分析说明,所提方法补偿后的测量结果的均方根误差为0.003 9,比利用分段补偿后的测量结果0.005 2更为精确.

In acoustic resonance based liquid level measurement, the measurement error is compensated according to piecewise function of level heights. Obviously, this kind of compensation is not accurate enough. In order to deal with this problem, a new compensation method is presented based on the belief rule base（BRB）. Because the measurement errors at different liquid level heights are closely related to the parameters such as the number of standing waves in the synthetic acoustic wave, the mean values and the standard deviations of the frequency difference between adjacent standing waves. The BRB can be used to model the complex nonlinear relationship between these parameters （inputs） and compensation value （output）. When the values of the input parameters are obtained at a certain level height the belief rules activated by the inputs are combined by the evidential reasoning（ER） algorithm so as to obtain the fused belief structure about the compensation, and then, the accurate measurement results can be calculated from the fused result. Finally, the liquid level measurement experiment shows that the measured results after compensation by the proposed method are more accurate than those using the piecewise compensation method.