科氏流量计幅值控制中两类关键参数的确定

Determination of two types of key parameters in coriolis flowmeter amplitude control

为了实现科氏质量流量计的数字驱动,需设计有效的幅值控制方法以控制流量管的振幅。为此,建立被控对象的数学模型,提出两类关键参数的确定方法,包括对数误差底数和不同流量管的比例积分(PI)参数。其中,利用有限长度的正弦波激励流量管,建立流量管振动系统的二阶数学模型。它在稳态下相当于一个固有增益,这为PI参数的整定提供了基准。根据期望值的不同,选取不同底的对数误差作为后续控制器的输入,以满足对动态特性和稳态特性的要求。采用PI控制器控制幅值,以幅值闭环系统的增益预设PI参数,再根据实际的动态效果和稳态效果确定最终参数。控制不同的流量管时,根据它们的稳态特性按比例关系调节PI参数。

It is necessary to design an effective amplitude control method to control the amplitude of the flow tube in order to achieve the digital drive of Coriolis mass flowmeters. For this purpose, a mathematical model of the controlled object is established, and methods for determining two types of key parameters are proposed, including the logarithmic error base and proportional integral(PI) parameters for different flow tubes. A finite length sine wave was used to trigger the flow tube, then the second-order mathematical model of the flow tube vibration system was established. The flow tube vibration system is equivalent to an inherent gain in the steady state, which provides a benchmark for setting the PI parameters. According to the difference of expected values, the logarithmic error of different bases is selected as the input of the subsequent controller so as to meet the requirements for the dynamic characteristics and the steady-state characteristics. The PI controller is used to control the amplitude and the gain of the closed-loop system is used to preset the PI parameters. The final parameters are determined according to the actual dynamic table effect and the steady state effect. When controlling different flow tubes, PI parameters can be adjusted proportionally based on their steady-state characteristics.