Development Of The Immersion Thermal Gas Flowmeter With Low Power Consumption

Gas flow measurement is always an important part of flow research.It is closely linked to our country's industrial technology development and economic level improvement,Thermal flowmeter is a new type of gas flow meter.Its measurement principle is based on the heat transfer principle and it is the measurement for mass flow.It can be divided into the distribution type and the immersion type according to the structure.The distribution type is used in small flow of gas and the immersion type is mainly used in the measurement of high flow rate of gas.Nowadays,the immersion thermal gas flowmeter has the characteristic of high power consumption and low measurement accuracy in small flow rate.So it cannot be applied in different area because of these deficiencies.In order to solve these problem,a low power gas flow measurement method is proposed.The sensor structure is optimized and the sensor temperature characteristics are studied.The gas flow meter with temperature compensation automatically is designed.The dynamic characteristics of the flow sensor are studied and the power consumption of the meter is reduced by controlling the power supply with PWM.The reseach has practical value to the development of the thermal flowmeter.In this paper,the influence of different sensor structure models on the gas flow field is firstly studied.Four kinds of sensor structures are established by using SolidWorks and simulated by FLUENT software.The best sensor structure model is determined by the ratio method.Then the temperature characteristics of the sensor are studied,the working temperature is determined to design the temperature compensation circuit.At the same time,a new flow measurement method is proposed by studying the dynamic performance of the sensor.The measurement with low power consumption is implemented by controlling the power supply.The flowmeter hardware circuit is designed.The sensor circuit is used to collect gas flow signals and signal processing circuit is used for the signal pre-processing.The MCU is used to complete the signal analysis and display.Finally the design of the system software is designed.It include the program of flow calculation,data storage and human-machine interface.The gas flow standard device for testing the flowmeter prototype is designed in the paper.The experimental studies show that the accuracy grade of flowmeter prototype is 1.5,the repeatability is less than 0.5%and the range ratio is 120:1.The low power characteristics of the flowmeter are measured.The duty cycle of 20%and the frequency of 0.5Hz are used in the supply control of PWM.The power consumption is reduced about 4 times than the normal supply.