Research Of DN80 Four-paths Gas Ultrasonic Flowmeter

The adaptability of ultrasonic flowmeters is theoretically studied to solve the problems that the accuracy of such flowmeters is generally affected by uneven airflow and temperature changes.Furthermore,this paper develops a four-path gas ultrasonic flowmeter to prepare for the upgrading of measuring instruments,such as coke oven gas and other gas flow meters.The main tasks are as follows:(1)The accuracy of a flowmeter is related to the length that temperature sensor extrudes in a gas pipeline,the relations is researched by means of combining simulation and experiment for our DN50 and DN80 flowmeters.The research results illustrate: Difference penetration lengths only affect the velocity distribution of path 1 of the four path.In the course of the simulation and experiment,the relative errors caused by different extruding lengths are recorded.From the records,we can come to conclusions about optimal length that the sensor extrudes into pipeline: for DN50 flowmeter,we suggest to be 6mm,for DN80 flowmeter,suggest to be 8mm.(2)In order to research how installation angles influence the accuracy of the meter,seven simulation model between 30 ° and 60 °(every 5 degree)is established.The simulation shows that the quantity of the installation angles mainly affects the distribution of speed in that the gas flows near the grooves in the paths.Finally,the optimal installation angle is suggested to be 50° by analyzing the relative error of the simulated velocity of different installation angles.(3)After developing a prototype of gas ultrasonic flowmeter.It adopts a parallel crosstype four-path arrangement,and completes the circuit hardware and the software.The prototype circuit performance is stable and easy to use by debugging repeatedly.(4)A series of measurement experiment is carried on in the laboratory of our university.Data of inherent deviation and each path length of the prototype is obtained by the static flow experiment;At the same time,the test results of the prototype test prove that most of the flow points of the prototype are within the range of the index,it repeatability is only0.214% in the high area flow(45-180 m3/h),and the lowest is 0.117%;the repeatability in the low area flow can reach 0.092%.Therefore,the four-path gas ultrasonic flowmeter designed in this paper has reached the test standard of the 1.0-level precision instrument at the 3-180m3/h flow point under the laboratory test environment.(5)A zero crossing detection method combining automatic gain and normalized amplitude was firstly used in the design of the flow meter.This method reduces the fluctuation of the amplitude of the echo signal at different flows and temperatures;Improving the accuracy of feature-wave localization of the echo signal;Thereby,Improving measuring accuracy of the propagation time.In addition,median average filtering algorithm is adopted to further reduce the interference of noise on the measurement accuracy of the propagation time.