Study On MEMS Thermal Flow Sensor

Flow measurement is widely used in daily life and industrial fields.According to different measurement principles,the flow detection method can be divided into turbine type,vortex type,ultrasonic type,heat transfer type,etc.,among which the thermal type flow sensor has been widely used in recent years due to its simple structure,no mechanical parts and high measurement accuracy..With the rise of MEMS technology in the 1990 s,the use of MEMS technology to produce various types of thermal flow sensors has the characteristics of high measurement accuracy,low power consumption,and good detection performance,making the thermal flow sensor based on MEMS technology become available and a great development.In this work,we design a thermal flow sensor based on MEMS technology,and the problems involved in the design,fabrication and calibration process of the thermal flow sensor based on MEMS technology are analyzed,modeled,simulated and tested.First,according to the knowledge of fluid mechanics and the equation of motion and heat transfer equation of fluid,a mechanical model of flow sensor is established,and the flow of fluid in a solid pipe is analyzed.On this basis,by introducing the concept of the boundary layer flow,the thermal boundary layer flow problem under heat condition is analyzed.The COMSOL simulation software is used to model the flow sensor,to obtain the temperature distribution of up and downstream Thermometer resistance under at different flow rates,and discuss the relationship between the flow rate and the temperature difference of the Thermometer resistances.The design and production process of the MEMS thermal flow sensor are introduced and analyzed.The peripheral control circuit and test detection system of the flow sensor are designed,including the flow acquisition circuit,the constant temperature difference circuit,the differential amplification circuit,the digital control circuit and the serial communication circuit.Finally,we calibrate the designed flow sensor based on PC software,verify the reliability of the flow sensor design.