Research On Some Problems Of Multi-path Ultrasonic Gas Flow Measurement

Ultrasonic gas flowmeters have gained more and more attention and have been applied in many fields because of their advantages such as high measurement accuracy,good measurement repeatability,wide measurement range ratio,low pressure loss and so on.Ultrasonic gas flowmeters can be divided into the single-path flowmeters and the multi-path flowmeters according to the number of acoustic paths.Compared with the single-path ultrasonic gas flowmeters,the multi-path ultrasonic gas flowmeters can effectively reduce the influence of asymmetry distribution of airflow velocity profile in the pipeline and it has many advantages,such as higher precision,stronger anti-interference ability,especially suitable for large-diameter flowrate measurement.So,the multi-path ultrasonic gas flowmeters have been more and more widely applied in the field of natural gas trade measurement.Because the study of multi-path ultrasonic gas flowmeters started late in China,there are many technical problems to be solved.In this paper,several problems of multi-path ultrasonic gas flowrate measurement are studied,includeing the design of multi-path sensors,the system design of multi-path ultrasonic gas flowmeters,the acoustic path fault diagnosis and compensation,and the gas flowrate measurement experiments.This paper focuses on the study of the dual-path ultrasonic gas flowmeter and the four-path ultrasonic gas flowmeter.The appropriate acoustic path arrangement construction and flowrate integration method are selected to overcome the influence of flow velocity distribution on the measurement in difference airflow conditions and hence to improve the performance of the ultrasonic gas flowmeters.The main work and innovations of this paper are listed as follows:(1)Concerning the gas flowrate measurement under different pipe diameters,two kinds of multi-path ultrasonic gas flowrate measurement sensors with different acoustic path arrangement methods are designed,namely dual-path "Z+V" sensor and four-path "X+X" sensor.Meanwhile,the flowrate integration methods used in these two multi-path sensors are studied.(2)The ultrasonic signal transmitting circuit,the ultrasonic signal receiving circuit,the multi-path switching circuit are designed and developed,and the whole system is debugged.Meanwhile,based on the model fitting method,the fitting model of the receiving ultrasonic signal is established,and the flowrate calculation of the multi-path ultrasonic gas flowmeters is completed.(3)A method of acoustic path fault diagnosis and compensation is proposed,aiming at solving the problem of acoustic path failure during the operation of the multi-path ultrasonic gas flowmeter.Firstly,the position of the abnormal acoustic path is determined online by measuring the sound velocity.Then,the weight coefficients of the normal working acoustic paths are adjusted to reduce the error of flowrate measurement caused by the acoustic path failure.Finally,the effectiveness of this compensation method is verified by experiments.(4)Dynamic flowrate measurement experiments are carried out in a standard sonic nozzle gas flow experimental system and the performance of the dual-path"Z+V" ultrasonic gas flowmeter prototype and the four-path "X+X" ultrasonic gas flowmeter prototype are tested,respectively.The flowrate measurement values of the two multi-path ultrasonic gas flowmeters are calibrated,respectively.