Fang Min, Xu Ke-Jun, Zhu Wen-Jiao, Shen Zi-Wen
School of Electrical and Automation Engineering, Hefei University of Technology, Hefei 230009, People's Republic of China.
Rev Sci Instrum. 2016 Jan;87(1):015107. doi: 10.1063/1.4939670.
Most of the ultrasonic gas flow-meters measure the gas flow rate by calculating the ultrasonic transmission time difference between the downstream and upstream. Ultrasonic energy attenuation occurs in the processes of the ultrasonic generation, conversion, transmission, and reception. Additionally, at the same time, the gas flow will also affect the ultrasonic propagation during the measurement, which results in the ultrasonic energy attenuation and the offset of ultrasonic propagation path. Thus, the ultrasonic energy received by the transducer is weaker. When the gas flow rate increases, this effect becomes more apparent. It leads to the measurement accuracy reduced, and the measurement range narrowed. An energy transfer model, where the ultrasonic gas flow-meter under without/with the gas flow, is established by adopting the statistical analysis and curve fitting based on a large amount of experimental data. The static sub model without the gas flow expresses the energy conversion efficiency of ultrasonic gas transducers, and the dynamic sub model with the gas flow reflects the energy attenuation pattern following the flow rate variations. The mathematical model can be used to determine the minimum energy of the excitation signal for meeting the requirement of specific measurement range, and predict the maximum measurable flow rate in the case of fixed energy of excitation signal. Based on the above studies, a method to enhance the excitation signal energy is proposed under the output power of the transmitting circuit being a finite value so as to extend the measurement rage of ultrasonic gas flow-meter.
大多数超声气体流量计通过计算下游和上游之间的超声传输时间差来测量气体流速。超声能量在超声产生、转换、传输和接收过程中会发生衰减。此外，在测量过程中，气体流动同时也会影响超声传播，这会导致超声能量衰减以及超声传播路径的偏移。因此，换能器接收到的超声能量较弱。当气体流速增加时，这种影响变得更加明显。这会导致测量精度降低，测量范围变窄。通过基于大量实验数据进行统计分析和曲线拟合，建立了超声气体流量计在无气流/有气流情况下的能量传递模型。无气流的静态子模型表示超声气体换能器的能量转换效率，有气流的动态子模型反映了随流速变化的能量衰减模式。该数学模型可用于确定满足特定测量范围要求的激励信号的最小能量，并在激励信号能量固定的情况下预测最大可测量流速。基于上述研究，在发射电路输出功率为有限值的情况下，提出了一种增强激励信号能量的方法，以扩展超声气体流量计的测量范围。
