Research On Control Method And Testing Technologies Of MEMS Thermal Wind Sensor

MEMS technology has attracted much attention due to its miniaturization,integration and mass production.Wind speed and direction detection is an indispensable reference in agricultural production,transportation,weather forecasting and sports events.As a result,research on MEMS anemometer is very important.Our laboratory has been engaged in research on MEMS thermal wind sensor for many years,and has accumulated lots of experience in this area,however,in order to meet commercial requirements,it is necessary to simplify the circuit to facilitate multiple modes of measurement and suppress temperature drift to improve sensor performance.In this paper,the PID algorithm is used to realize the constant temperature difference control mode,the sensor chip with three different packages and structures are taken as the research objects,the purpose is optimizing the hardware circuit as well as suppressing the temperature drift of the sensor.A new trial test method is to measure ambient temperature and chip temperature with measuring elements on chip,focus on the impact of new software control method on sensor performance,the main contents are as follows:Firstly,as for the hardware circuit,on the one hand,the control circuit is simplified,and the parts of the power supply,sampling,signal processing,display and microcontroller are reserved on the hardware circuit,and the part that feedbacks the heating power is no longer included,new circuit supports constant temperature difference mode,constant current mode,constant voltage mode and other modes of measurement,on the other hand,removing the ambient temperature sensor,using the temperature measuring component on the chip to simultaneously measure the ambient temperature and the chip temperature can effectively suppress temperature drift caused by the inconsistent temperature coefficient of the temperature measuring component;in software,combining the microcontroller's interrupt program and timing program to measure the ambient temperature and chip temperature in a time-sharing method,using the PID algorithm to achieve constant temperature difference control,adjusting the algorithm parameters to shorten the sensor's hot start time and measurement period,and the sampled data is filtered to achieve output stability.Secondly,from the perspective of commercialization of wind sensor,the circuit is simplified for a low-dispersion,low-error ceramic chip-based sensor chip,and the ambient temperature and chip temperature are measured by transistor on the sensor chip,the ambient temperature output is stable,after adjusting the parameters of the PID control algorithm,the hot start time under software control is 12.98 s when?T equals to 15°C,and the time from₍?6?+?to₍?6? is 23.1 s under windless conditions,when the wind speed is 37.1 m/s,wind output does not reach saturation,the wind speed measurement error is less than 1m/s within full scale,wind direction measurement error is less than 2.2°,and the zero point temperature drift offset is less than 1 m/s comparing with 20°C.Thirdly,for the purpose of low power consumption,a sensor chip based on ceramic film package is designed,the ambient temperature and chip temperature are measured by a heating resistor located at the center of the chip,when?T equals to 20°C,the hot start time of the sensor based on this mode is less than 6s,then adjusting the resistance of the voltage divider resistor by adding a MOS tube,the power consumption of the whole sensor system is reduced to 397.26mW,under no wind conditions,the power consumption of the heating resistor on the sensor chip is 111 mW.After lower the work frequency,the total power consumption is reduced to 331mW,the wind speed error is less than 2 m/s,and the wind direction error is less than 5°,the performance is equivalent to the hardware control method.Lastly,on the basis of ceramic film packaging,in order to reduce the power consumption of the sensor,a sensor chip based on glass substrate is proposed,the structure and element parameters are equivalent to those based on ceramic film,control circuit is same as the sensor of the ceramic substrate,when?T equals to 7°C,when the wind speed is 5 m/s,the power consumption of the chip is 34 mW.Wind speed measurement error is less than 1 m/s,wind direction error is less than 2°,hot start time is 7 s when there is no wind,wind speed output is close to saturation when wind speed is 20 m/s.at 0⁵5°C,the zero output changes in the x direction by 0.026 V,the y direction changes by 0.0078 V,and the change of y direction can be ignored,the temperature drift is suppressed.The experimental results of the three sensors show that the new control method can suppress the temperature drift while ensuring the performance of the sensor.The new method solves the dual functions of ambient temperature measurement and constant temperature difference control mode realization,so that the wind sensor system avoids the extra package of temperature sensor,which greatly simplifies the package.The adjustment of the software algorithm parameters shortens the sensor's hot start time and measurement period.