Research On Signal Sampling And Processing Technology Of Multi-channel Gas Ultrasonic Flowmeter

Gas ultrasonic flowmeter has high precision and stable system,which is widely used in industry,especially in natural gas trade and other fields.However,the market of gas ultrasonic flowmeter is almost monopolized by foreign manufacturers,and there are few gas ultrasonic flowmeter manufacturers with high precision and good performance in China.For this purpose,from the point of view of signal sampling and processing in flowmeter,the characteristics of ultrasonic signal are deeply analyzed,and an algorithm for ultrasonic signal processing is designed,which can effectively improve the accuracy,and is implemented on the gas ultrasonic flowmeter system based on DSP.This topic takes the DSP chip as the core.The circuit system consists of excitation signal conditioning circuit,received signal conditioning circuit,timer circuit and so on.The functions of transducer excitation,received signal processing,flow calculation,flow output,communication with host computer are implemented.In view of the need of transducer switching in multi-channel flowmeter,a reasonable transducer switching circuit is designed to control the switching of the whole transducer with a 3-8 decoder.Double-threshold method is used for single channel measurement.In view of the frequently occurring error phenomenon in double-threshold method,the physical characteristics of the received signal and the causes of the error phenomenon are analyzed in depth,and an improved method based on peak-slope method is designed.This method finds the correct characteristic wave according to the relationship between the peaks of the received signal,and reduces the occurrence of the error phenomenon reasonably and effectively.For the zero-crossing time error caused by the limit of sampling frequency,the Lagrange interpolation algorithm is used to find a more accurate zero-crossing time,and the interpolation algorithm is improved to reduce the computational complexity and improve the computational efficiency.This topic is a four-channel cross-layout flowmeter.For the fourchannel flow data,the real-time flow in the pipeline is calculated using the Gaussian-Jacobian numerical integration method.In order to verify the accuracy and repeatability of the flowmeter system,a field flow calibration experiment was carried out on the flowmeter prototype in the calibration laboratory of SOLVETECH Automation Technology Co.,Ltd.in Tianjin using DN200 pipeline.The experimental results show that the accuracy and repeatability of the flowmeter meet the requirements of the standard(JJG 1030-2007)for accuracy level 1.0 flowmeters.