Design And Experiment Of Measurement And Control Circuits For Flexible MEMS Flow Sensor

Flow sensors have been widely used in many fields such as daily life,industrial manufacturing,scientific research,aerospace and military production.A wide range of applications makes performance of the flow sensors be required strictly.In view of problems of the existing MEMS flow sensors such as small measuring range and not being applied to the curved surface,a type of MEMS flow sensor based on a flexible material substrate,which mainly includes a heating resistor and three pairs of temperature-measuring resistors,was designed and fabricated,and wide measuring range of flow velocity could be achieved by the combination of working principles of anemometer and calorimetric flowmeter.This thesis mainly studies measurement and control circuit and flow measurement experiment of the flexible MEMS flow sensor,and the main work is concluded as follows:?1?The working principle,designed structure and micro-fabrication process of flexible MEMS flow sensor are introduced.By selecting polyimide?PI?as flexible film material and platinum?Pt?film as thermal resistance material,a flexible MEMS flow sensor chip with a cavity was fabricated.?2?The time-domain modeling of flexible flow rate sensor heating resistance control circuit by MATLAB/Simulink is simulated.The simulation results of working temperature and working voltage were analyzed.And the selection of RC constant was determined according to the result of transient analysis of working temperature.The simulation results show that the design working temperature is 67.5?,the working voltage simulation value is 7.3V.These results provide a theoretical basis for the design of constant temperature difference measurement and control circuit.?3?The measurement and control circuit of flexible flow sensor and multi-channel A/D conversion sampling system based on STM32microprocessor were designed.In order to measure the different flow speed accurately,high flow speed and low flow speed measurement and control circuits were designed respectively.The high speed measurement and control circuit was designed with constant temperature differential mode of operation and dual Wheatstone bridges circuit with temperature compensation.The low speed measurement and control circuit consists of three routes of Wheatstone bridge circuit,each route includes a pair of temperature-measuring resistors.The high speed and low speed measurement and control circuits were simulated by Multisim,and the PCB board was designed by Altium Designer.In order to simultaneously sample and digitize the four flow measurement output signals of the sensor measurement and control circuits,a multi-channel A/D conversion sampling system based on the STM32 microprocessor is designed.?4?Test experiment of the flexible flow sensor.A high flow speed and a low flow speed measurement experiment system for generating accuarate wind speed was built.The test results show that the flow sensor could measure the input wind speed in the range of 0 to 32 m/s,and the sensor has a high sensitivity at low wind speeds under 1m/s was about 100 mV/m·s^-1,and the sensitivities at high wind speeds of?1⁷ m/s?and?7³2 m/s?were83.1 mV/m·s^-1 and 28.3 mV/m·s^-1 respectively.This proposed flexible MEMS flow sensor can be applied to the curved surface with wide measurement range and high precision,which will have a wide application prospect.