Research And Development Of Thermal Gas Mass Micro Flowmeter

Thermal gas mass flow meters are a hot research topic today,including hot wire anemometers,thermal distributed gas mass flow meters,plug-in gas mass flow meters,and so on.In terms of measurement applications,thermal distribution gas mass flow meters are mainly used to measure low-speed and small flow rates.The plug-in gas mass flowmeter is biased to measure the volume flow of medium and high velocity gas,which is suitable for the measurement of gas flow in large and medium-sized pipelines.At present,the thermal gas mass flow meters on the market that can be used to measure corrosive gases,poisonous gases and other gases required by the nuclear industry and special chemical industries are all products from the 1970 s and 1980 s,and their measurement accuracy is high(5%).After entering the market economy,due to the small demand for this type of flowmeter and the narrow application range,its development progress has been in a blank for a long time.The research in this thesis is based on the above-mentioned status quo,and the purpose is to design a high-precision thermal gas mass micro-flowmeter that can be used for micro-flow corrosion/toxic gas measurement.After confirming the design goal,after plan comparison and functional requirements consideration for thermal gas mass flowmeter sensor measurement,the sensor measuring tube measurement plan is determined to be a non-contact pipe section heat distribution type measurement,and the sensor measuring tube is designed and selected according to this measurement plan.Using the STM32L072 LZT single-chip microcomputer as the main control chip,based on the functional modular design idea,design the signal amplifier module,voltage constant current source module,data display communication module circuit,etc.,select high-precision devices to improve the measurement accuracy in device selection.The paper adopts a time-sharing program structure,and the functional modules are divided into different time periods,which reduces the coupling between program modules and facilitates the management and upgrade of each functional sub-module and system maintenance.After the completion of the above work,an experimental platform was designed to debug the performance of the flowmeter,and the designed measurement accuracy was tested.Through the analysis and linear fitting of the measurement data,the final measurement accuracy was in line with the design expectations.At the same time,the experimental results showed that the subject The measurement accuracy of the thermal gas mass micro flowmeter developed and designed has reached 3% of the set value,while the measurement range satisfies 0.5L/h-10L/h.