Study On Key Technology Of Multi-channel Ultrasonic Gas Flowmeter Signal Processing Based On Zero-crossing Detection

Ultrasonic gas flowmeter is used in the chemical industry,metallurgy,natural gas trade measurement and civil gas and other fields because it possesses the features,such as high measurement accuracy,range ratio,no pressure loss and suitable for large diameter measurement,and has broad prospects for development.Ultrasonic gas flowmeter has become the focus of flowmeter research and hot spot of flowmeter application.The signal processing methods of the four-channel ultrasonic gas flowmeter are studied in order to calculate the gas flow rate accurately.A signal processing method based on zero-crossing detection and energy change rate is proposed.According to the variation pattern of the echo signal energy from the ultrasonic gas flowmeter,the arrival time of the echo signal is determined,and the propagation time of the echo signal is calculated to obtain the gas flow rate.The zero phase filtering method is used to filter out the noise signal in the echo signal and retain the phase information.A Kalman filter based fusion method is proposed for the measurement results of the multi-channel ultrasonic gas flowmeter.It can automatically adjust the weight of the measurement result of each channel according to the statistical law of each channel calculation result,deal with the abnormal value and realize more stable output.The software of the four-channel ultrasonic gas flowmeter is developed,and the proposed signal processing method and instrument functions are achieved.The software of the DSP system is developed to realizes the pretreatment of ultrasonic gas echo signal,the signal processing method based on zero crossing detection and energy change rate,flow calculation,Kalman filter fusion,flow result pulse output and flow result display.The GUI software of the PC is developed to communicate with the four-channel ultrasonic gas flowmeter through the serial port,and display the received gas flow information in graphical and textual form.The key performance indexes of the four-channel ultrasonic gas flowmeter is tested in order to verify the effectiveness of the proposed methods and the developed system.The gas solidification calibration experiment was carried out in Chongqing Institute of Metrology and Quality Inspection,which was accredited by the State.The experimental results show that the indication error is 0.20% and the repeatability is 0.04%.The key performance indexes,such as indication error and repeatability,of the developed four-channel ultrasonic gas flowmeter is far superior to the requirements of 1-level accuracy in the verification regulation.