Research And Design Of Multi-channel Gas Ultrasonic Floemeter Based On FPGA

The multi-channel gas ultrasonic flowmeter is favored by users because of its advantages of high precision,good stability,and strong adaptability to the flow field.It plays an important role in industrial flow measurement and trade measurement.The thesis focuses on the measurement principle,the influencing factors of precision,temperature and pressure compensation,system design based on FPGA,and the optimization of multi-channel weight coefficient assignment of multi-channel gas ultrasonic flowmeter.The flowmeter adopts the measuring principle of transit-time method and the channels are arranged in parallel intersection.In this paper,the measurement principle of the gas ultrasonic flowmeter,the factors which influence the measurement precision and the temperature pressure compensation method are analyzed theoretically;The system design of ultrasonic flowmeter is based on field programmable gate array(FPGA),including the ultrasonic pulse trigger circuit,high precision time measurement circuit,multi-channel switching logic control circuit,and communication with the microcontroller circuit et al to achieve the control of peripheral devices and high-precision measurement of gas flow.Combining the traditional Gauss-Jacobi integration method and circular tube optimal integration method in the world,the measurement results will have large errors caused by a single transducer working abnormally.In the case of large errors,it is proposed that the weighted data fusion algorithm can be used to calculate the optimal weight coefficient adaptively,making the measurement results of the flowmeter more accurate.When under the condition of non-ideal flow field,proposed that the nonlinear least squares method is used to calculate the weight of each channel coefficients,and verifying the simulation of nonlinear least square method by using CFD simulation software FLUENT.Finally,by applying the calibration environment of zhonghuan TIG Co.,LTD,we calibrate the prototype of the ultrasonic flowmeter on the diameter pipes of DN100.The calibration results show that the precision grade and repeatability of the prototype meet the requirements of the 1 level table,and meet the measurement requirements of most industrial sites.