【作者】 张扬；

【导师】 孙立军；

【作者基本信息】 天津大学 ， 控制科学与工程， 2019， 硕士

【摘要】 科里奥利流量计具有非常高的质量流量测量精度,并且可以提供多参数的测量如密度、温度、体积流量等,被广泛应用于工业流量测量。科里奥利流量计依靠测量管的振动测得质量流量,测量管的特性直接影响流量校准系数。潜在的侵蚀或腐蚀会降低管壁厚度并影响其测量性能,严重情况下甚至可能导致结构完整性问题。由于管壁厚度直接影响其刚度,因此与刚度相关的诊断参数有助于识别潜在的测量和结构完整性问题。科里奥利流量计通常用于单相流体,即液体或气体。如果液体中夹带气体,其测量精度就可能受到影响。两相流工况中,测量管的阻尼比不断变化,由气体夹带引起的显著增加的压缩性也会给科里奥利流量计的现场应用带来困难。本文从流量校准系数和气液两相流测量误差两个方面入手,进行了以下研究工作:(1)构建测量管的单自由度振动模型,基于该模型的频率响应函数推导刚度计算公式。在驱动信号中增加一个附加频率的信号,结合正交解调算法、滤波器设计、锁相环、PID控制、控制环路设计、有限元分析的方法,实现刚度计算。(2)气液两相流工况下,对测量管中的气泡进行受力分析,根据气液的振动差异提出补偿方法;构建测量管内气泡压缩的谐振器模型,对测量管的振动模态进行有限元仿真和伯德图分析,通过两个频率的驱动信号使测量管同时在第一模态和第三模态下振动,使用振动特性补偿测量误差。(3)以DSP为硬件平台,根据仿真模型编写科里奥利流量计传感器的控制算法、刚度算法、气泡补偿算法、双模补偿算法;编写上位机程序,实现测量数据的实时监测与参数修改;对刚度算法和补偿算法进行实验测试,实验结果表明,刚度算法可以跟踪测量管刚度的变化,补偿算法可以显著改善科里奥利流量计测量气液两相流时的精度。更多还原

【Abstract】 Coriolis flowmeters have an excellent performance in mass flow measurement.They are widely used in industrial flow measurement,which can provide multi-parameter measurements such as density,temperature and volume flow.Coriolis flowmeters rely on oscillating tubes to sense fluid flows.The characteristics of the measuring tube directly affect the flow calibration factor.However,potential erosion or corrosion can reduce the tube wall thickness and affect their measurement performance,and severe thickness reduction may even result in structural integrity issues.As the tube thickness directly affects their stiffness,a diagnostic parameter related to stiffness will aid the diagnostics of potential measurement and structural integrity issues.Coriolis flowmeters are usually used for single phase fluids,that is liquids or gases.If the gas is entrained in the liquid,the measurement accuracy may be affected by the two-phase flow.In the two-phase flow condition,the damping ratio of the measuring tube is constantly changing,and the significantly increased compressibility caused by the gas entrainment also brings difficulties to the field application of the Coriolis flowmeters.In this thesis,the following research work is carried out from two aspects: flow calibration factor and measurement error of gas-liquid two-phase flow:(1)A single degree of freedom vibration model of the measuring tube was constructed.Based on the frequency response function of the model,the stiffness calculation formula is derived.By adding an additional frequency signal to the excitation signal,and then combining the quadrature demodulation algorithm,filter design,phase-locked loop,PID control,control loop design,and finite element analysis,stiffness calculation has been achieved.(2)Under the condition of gas-liquid two-phase flow,the force analysis of the bubbles in the measuring tube was carried out.The compensation method is proposed based on the vibration difference of gas and liquid.A resonator model for measuring bubble compression in the tube was constructed.Finite element simulation and Bode diagram analysis were performed on the vibration mode of the measuring tube.The combined excitation signal of the two frequencies is used to cause the measuring tube to vibrate simultaneously in the first mode and the third mode.Vibration characteristics are used to compensate for measurement errors.(3)According to the simulation model,the control algorithm,stiffness algorithm,bubble compensation algorithm and dual-mode compensation algorithm have been implemented on a commercially available DSP hardware platform.A PC program was also developed to realize real-time monitoring and parameter modification.The stiffness algorithm and the compensation algorithm were tested experimentally.The experimental results show that the stiffness algorithm can track the change of the stiffness of the measuring tube,and the compensation algorithm can significantly improve the accuracy of the Coriolis flowmeters when measuring the gas-liquid two-phase flow.更多还原