Study And Implementation Of Processing Method For Ultrasonic Gas Flowmeter Signal Based On Variable Threshold Zero-crossing Detection

Compared with some traditional gas flow meters, gas ultrasonic flowmeter has the advantages of high measurement precision, wide measuring range, no pressure loss, etc.. It is widely used in gas trade, chemical industry, and has broad prospects for development. Domestic gas ultrasonic flowmeter market is almost monopolized by foreign brands. There are only a handful of domestic companies producing gas ultrasonic flowmeter, whose products do not use digital signal processing methods, and their performance needs to be improved. To this end, a digital signal processing method with high accuracy, good real-time performance ultrasonic for gas flowmeter is proposed and realized in real time on a system with DSP and FPGA as the core.Aiming at the difficulty in determining feature point in the signal processing of gas ultrasonic flowmeter, a variable threshold based zero-crossing detection signal processing method is proposed to determine a feature wave of the signal accurately. Thus the propagation time of ultrasonic signal is calculated, and the gas flow rate is measured accurately.This method is realized real time in a signal processing system with DSP and FPGA for the gas ultrasonic flowmeter. DSP system software is developed, and signal preprocessing, variable threshold based zero-crossing detection algorithm, flow rate calculation, flow display, flow information output, flow signals uploaded to the host computer are realized in real time. In the software, by judging the "step", the error caused by noise interference is eliminated, and the stability of the measurement results is enhanced. With piecewise linear calibration, the non-linear error is corrected, and the measurement accuracy of the system is improved. Gas flow calibration experimental results verify the effectiveness of the method and the system.To verify the validity of the signal processing method and system, gas ultrasonic flowmeter calibration experiments are conducted in Chongqing Academy of Science and Technology and Chongqing Academy of Metrology and Quality Inspection respectively. The experimental results show that the measurement accuracy is 1%, meeting the national standard (GB/T 18604-2001) requirements for 1-level precision ultrasonic gas flowmeter, and the requirements of the commissioning party.