Development Of A Miniature Thermal Wind Sensor

The measurement of wind speed and direction is closely related to our daily life.As two important indicators for meteorological monitoring,it is important to measure them timely and accurately.Currently,a number of measuring instruments are employed in the meteorological industry such as cup anemometers,ultrasonic anemometers and thermal anemometers.While all of these instruments have their advantages,there is a lack of miniature wind speed and direction measurement equipment on the market.Miniaturization of measuring instrument is the trend of future development,which facilitates portability,deployment and removal,and is also an important means of further extending measurement elements and functionality or increasing range in restricted environment.To achieve a miniaturised,integrated,lowcost and simultaneous measurement of wind speed and direction,in this project,a thermal wind sensor based on the interaction between the flow and temperature fields was designed,and the sensor was tested through a combination of simulation and experimental studies.The main contents are as follows:(1)A miniature thermal wind sensor model based on the thermal temperature difference principle was proposed.According to the heat transfer theory of thermal wind sensor,three forms of heat transfer during the operation of the sensor were analyzed.Meanwhile,the advantages and disadvantages of the three major wind measurement methods of the thermal wind sensor were outlined.The model was structured by the measuring core with NTC thermistors and a heating coil,distributed on a 20 mm diameter circular sheet base plate.The detection principle of thermal temperature difference was adopted.(2)The distribution law of thermal field in the flow field was analyzed by the fluid dynamics software FLUENT and the wind speed and direction discrimination was designed.In the meantime,the factors influencing the sensor testing of wind speed and direction were also analyzed.The simulation results showed that the high temperature coverage area of the thermal field under the action of the wind field was around ±35°,and the eight-way temperature measurement NTC scheme could obtain the thermal field distribution information more effectively.Compared Gaussian curve fitting with Fourier fitting to measure wind speed and direction based on the wind distribution law of the thermal field,the result showed that the latter still had a higher fitting accuracy at low wind speed.At the same time,the model structure of 1.0 mm heating coil pitch,3.6 mm temperature resistor pitch,20 mm base plate diameter and 1.2 mm base plate thickness could provide good sensitivity while ensuring the strength and miniaturization of the sensor.Finally,a linear interpolation error correction method was presented for the effect of wind speed determination due to ambient temperature variations.(3)As the core of the sensor system,reasonable design of hardware and software could greatly improve sensor performance.The STM32 microprocessor was adopted as the main control chip and the 24-bit high-precision ADS131M08 analog to digital conversion was used to collect the thermal field distribution information.The HMC5883 L,a geomagnetometer,was employed to achieve the automatic north setting function of the sensor.A heating power control circuit was designed to reduce the power consumption of the sensor,which can realize the conversion between constant power heating and pulse heating.The feasibility of the circuit was verified by software Multisim.In the software aspect,the project focused on the wind speed and direction measurement.Targeting the problem that the electronic magnetic compass HMC5883 L is susceptible to external magnetic field interference in wind direction measurement process,an elliptical hypothetical magnetic field correction scheme was proposed to ensure the accuracy of the compass.(4)To verify whether the sensor performance meets the design requirements,a wind speed and direction test platform was built.The experimental results showed that the designed thermal wind sensor could detect wind speed in the range of 1～30 m/s with an accuracy of 0.01 m/s and an error within ±(0.5+0.03v)m/s.The wind direction could be detected in the range of 0～360° with an accuracy of 0.1° and an error within±5°.The sensor was linearly interpolated to correct errors caused by ambient temperature and could operate normally at ambient temperatures from-10 to 40 °C with a maximum system power consumption of 0.635 W.