Research On The Key Technologies Of Transit Time Ultrasonic Gas Flowmeters

According to the principle of the transit time ultrasonic gas flowmeter, this article provides a systematic analysis of the various factors affecting the measurement errors, and focuses on the key factors that reduce the measurement accuracies, such as installation effects, flow adaptation, driving technique as well as time-of-flight algorithms. Along with the theoretical studies, this article discusses the optimal methods and develops a new type of ultrasonic gas flow meter.A systematic research has been investigated on the transducer installation effects and the flow adaptations in this article. Moreover, an analysis has been made regarding the relationships between the measurement accuracies and the transducer installation angle, channel layout, bending angle, Reynolds number, pipe diameter, wall roughness as well as the ultrasonic flow meter installation location. Furthermore, the data gathered from these calculations form the tolerance table. All the work mentioned above provide a quantifiable assessment method to evaluate the flow adaptation and the solutions to the ultrasonic gas flow meter optimization designing.A novel pulse-driven approache is studied in this article, in which the phase and amplitude modulation technologies are introduced into the designing. Then, by strictly controlling the pulse interval time and adjusting the pulse phase and amplitude, a new group of self-interference waveforms that has the self-diagnose features of SNR is achieved. Accordingly, the experimental results show that the transmitting time between the transducers can be calculated by phase detections, and the environment SNR situations can be discriminated by the characteristics of the time interval.Self-adaptive time-of-flight algorithms based on the high and low SNR situation are designed in this article, which are named zero-crossing tracking (ZCT) and time-shifted superposition method (TSS). The pulse width detection method used by ZCT algorithm is designed to avoid interferences and distortions of noise on the received envelope zero-crossings. Additionally, by increasing the received samples strength, the enhanced SNR situations can be carried out by TSS algorithm to overcome the effects of noise.A simulation platform is builded by using Labview and Simulink, and a variety of driving waveforms and time-of-flight algorithms are compared. The simulation results show that the self-interference waveforms and the self-adaptive time-of-flight algorithms can extend the scopes of the classical transit time ultrasonic gas flowmeter, and achieve the high precision measurements in different SNR situations. A prototype of ultrasonic gas flow meter is developed based on the self-interference driven waveforms and self-adaptive time-of-flight algorithm. Furthermore, the effectiveness of the algorithm is studied on an ultrasonic ranging platform. The results show that the self-adaptive time-of-flight algorithm can automatically select the appropriate algorithm to complete the time detection, and effectively improves the detection accuracies of the ultrasonic transit time and the stabilities. Moreover, according to national standards and American Gas Association (A.G.A) No.9 report, the prototype is verified in the flow calibration system. The experimental results from the dry calibration indicate that the proposed flowmeter prototype can meet the zero-flow verification test requirements of the A.G.A Report No.9. Additionally, the results derived from flow calibration prove that the system can operate stable and reliable. Furthermore, after the flow weight mean error (FWME) adjustment is applied, the prototype can achieve wide turn-down ratio and high-precision flow measurements.