流体流速对超声波流量测量精度的影响及校准

Influence of fluid velocity on ultrasonic wave flowrate measurement accuracy and its calibration

采用超声波时差法进行流量测量时,流体流速会使超声波折射角发生变化,但测量计算中超声波折射角仍按固定值处理,就会影响流量测量精度。首先分析流体流速对超声波沿顺流或逆流传播时间和传播位移水平分量的影响,得出超声波传播时间和传播位移水平分量分别与流速呈反比和正比关系,而且其变化趋势逆流比顺流更加明显。其次通过对超声波在流动介质中传播特性的分析,分别获得了流体流速与超声波传播时间及超声波传播位移水平分量的关系,上述关系都间接反映出流体流速使超声波传播轨迹发生了超声波偏移。最后根据超声波偏移会改变超声波折射角的结论,利用折射角正切值与超声波传播时间的曲线关系对流量测量值进行了校准。校准后流量测量精度可提高0.1729%~1.6233%,平均可提高0.6471%,且流速越高,校准效果越好。

When the ultrasonic wave time difference method is used for flowrate measurement,the fluid velocity causes the ultrasonic wave refraction angle to change.If the ultrasonic wave refraction angle is still treated as a fixed value in the measurement calculation,the accuracy of flowrate measurement is affected.Firstly,the influences of fluid velocity on the propagation time and the horizontal component of the propagation displacement along the downstream flow or upstream flow of an ultrasonic wave are analyzed.It is found that the propagation time and the horizontal component of the propagation displacement of the ultrasonic wave are inversely proportional and positively proportional to the flow velocity,respectively,and the changing trend in the upstream flow is more evident than that in the downstream flow.Secondly,through analyzing the propagation characteristics of the ultrasonic wave in flowing medium,the relationship between the propagation time&horizontal component of the propagation displacement and flow velocity is obtained.The above relationship indirectly reflects that the flow velocity causes the deviation of ultrasonic wave propagation path.Finally,based on the conclusion that the ultrasonic wave deviation can change the ultrasonic wave refraction angle,the curve relationship between the tangent of the refraction angle and the propagation time of the ultrasonic wave is used to calibrate the flowrate measurement value.After calibration,the accuracy of flowrate measurement can be improved by 0.1729%~1.6233%with an average of 0.6471%.It is also found that the higher the flowrate,the better the calibration effect.