利用互易性电路设计降低超声流量测量的零点误差和温度漂移

Reciprocal circuit design to reduce zero error and thermal drift in ultrasonic flow metering

超声流量测量系统中,严重影响时间差检测的准确度和稳定性的"零点误差"和"温度漂移"问题可以通过对测量系统互易性的改善加以改进。本文通过对测量系统等效电路模型的分析阐述了系统互易的成立条件,并提出了一种通过对激励和接收电路等效阻抗进行对称性设计提高测量系统互易性的测量电路。这一电路设计易于在仪表中实现,其中换能器的负载阻抗能够根据需要灵活设定。在实际测量管道上进行的实验证明,使用这样的电路设计进行流量测量,能够大幅降低零点误差并抑制温度漂移,使得流量测量结果更加准确稳定。

In ultrasonic flow metering system, the ＂zero-flow error＂ caused by the non-identical of signal waveforms received in both directions and the ＂thermal drift＂ caused by transducers＇ thermal characteristics which seriously de- teriorate the accuracy and stability of the transit-time difference（TTD） measurement can be improved by promoting the reciprocity of the measurement system. In this paper, the approaches to achieve reciprocal measurement system are discussed based on tbe analyses of the equivalent circuit model of the ultrasonic flow meters. Measurement circuits specially designed for improving the system reciprocity by matching the equivalent impedances of transmitting and re- ceiving circuits are proposed. In these designs, the load impedances of the transducers can be varied flexibly to meet varieties of requirements, and the designs are easy to implement in measurement instruments. Experiments performed on practical metering pipe show that, both the zero error and the thermal drift in the metering can be reduced by using proposed circuit design, the accuracy and stability of the flow rate measurement can be promoted.