Design And Experimental Research Of Ultra-clean Ultrasonic Flowmeter Based On Time Difference Method

In the semiconductor manufacturing,pharmaceutical and chemical industries,liquid flow measurement for the flow sensor cleanliness,accuracy and repeatability are very high requirements.Therefore,when designing the liquid flow sensor,non-contact measurement method and ultra-clean pipeline material should be adopted to avoid pollution,and the structure and control system of the measurement pipe segment of the flow sensor should be reasonably designed,so as to meet the requirements of cleanliness,accuracy and repeatability of the ultra-clean flow sensor.Because the ultrasonic signal can be transmitted through the medium,the ultrasonic flow measurement technology can meet the requirements of non-contact measurement.Fluorine resin material has excellent chemical inertia,will not release metals and ions and other pollutants,can ensure the cleanliness of the measured flow body,so the flow sensor of the fluid pipeline using high purity fluorine resin material(PFA or PTFE)production.Therefore,aiming at the performance requirements of ultra-clean,high-precision and good repeatability of liquid flow sensor,this thesis designs an ultra-clean ultrasonic flowmeter for liquid fluid measurement in the field of semiconductor manufacturing based on ultrasonic flow measurement technology,from the three aspects of measuring pipe section structural parameters,hardware circuit and software algorithm.The main work of this thesis is as follows:1.Structure design and production of ultra-clean ultrasonic flowmeter.The meter uses the π-type tube section structure,so that the ultrasonic transducer is installed in a coaxial way on both sides of the measuring tube section.Based on fluid simulation,the influence of different inlet pipe angles on the flow velocity distribution in the measured pipe section of ultra-clean ultrasonic flowmeter was analyzed,and the appropriate inlet pipe Angle was determined to be 45°.Based on the acoustic simulation,the attenuation law of ultrasonic propagation at different distances and the requirements of the theoretical time difference of upstream and downstream on the accuracy of the time measuring chip were analyzed.Considering the influence of acoustic attenuation and the accuracy of the time measuring chip,the appropriate length of effective measuring tube segment was selected as 80 mm.Using high purity PFA material,the fluid pipe section of ultra-clean ultrasonic flowmeter is made to ensure the ultra-clean performance of the fluid pipe section.2.Derivation of flow calculation method and parameter correction based on time difference method.The flow field simulation under different inlet velocity was carried out on the flow measurement pipe,and the velocity correction coefficient was calculated according to the average velocity on the sound channel and the average velocity in the measurement pipe segment,which was used to correct the measured velocity and the actual velocity of the fluid in the pipe.The forward and reverse flow propagation process of ultrasonic wave in steady-state background flow field was analyzed by fluid-acoustic coupling simulation.The flow calculation formula was derived by time difference method combined with the structure of measuring pipe segment.3.Design of control system of ultra-clean ultrasonic flowmeter based on time difference method.The hardware and software systems of the control system are designed respectively.The hardware part is divided into three modules: the main control module,the time measuring module and the flow display module.In order to meet the high precision performance requirements,the high precision time measuring chip TDC-GP22 is adopted in the hardware aspect of flight time measurement.Part of the software realizes flight time measurement,instantaneous flow calculation algorithm by time difference method,flow display function and Kalman filtering algorithm.4.Flow calibration and test of ultra-clean ultrasonic flowmeter.The flow calibration of the ultra-clean ultrasonic flowmeter prototype was carried out,and the flow compensation coefficient was obtained,which was used to correct the measured flow.According to the national metrological verification regulation "JJG1030-2007 Verification Regulation of ultrasonic flowmeter",the performance test of accuracy and repeatability of ultra-clean ultrasonic flowmeter is carried out.The results show that its accuracy can reach level 1.5 and repeatability error is less than 1.0%,which can meet the requirements of liquid flow measurement in semiconductor manufacturing,medicine and chemical industry.In this thesis,according to the requirements of cleanliness,precision and repeatability of ultraclean flow sensor,the design,simulation and test of ultra-clean liquid ultrasonic flowmeter are carried out to provide an ultra-clean and high-precision flow measurement scheme for semiconductor manufacturing,medicine,chemical industry and other fields.