The relationship between the output of differential pressure and flow of differential pressure flowmeter is nonlinear during measuring small flow.Implementing this nonlinear relationship in DCS is very difficult.According to the known diameter ratio of the standard orifice plate,the flow coefficient formula of standard orifice plate under certain application conditions is fitted with application of NURBS non uniform rational function.Meanwhile,using the simple multiplication and addition operation,NURBS function is used to express the input and output relation of the nonlinear relation in DCS.Finally,the differential pressure and flow relationship under the condition of small flow are determined through nonlinear iterative algorithm.The on-line nonlinear compensation of small flow measurement is realized,and the accuracy of flow measurement is improved.%小流量测量时,差压式流量计输出的差压与流量之间是非线性关系,在分散控制系统(DCS)中直接实施该非线性关系较困难.根据已知标准孔板的径比,用NURBS非均匀有理函数,拟合在特定应用条件下的标准孔板流量系数公式;并用简单的乘法和加法运算,在DCS中用NURBS函数表示该非线性关系的输入和输出关系;最后用非线性迭代算法确定在小流量条件下的差压和流量关系,从而实现小流量测量的在线非线性补偿,提高了流量测量的精度.
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