A High-altitude Water Vapor Measurement System Based On Real-time Operating System

In the field of atmospheric detection,humidity is an important research parameter.It provides the fundamental information for weather monitoring and forecasting.Its accuracy will directly affect the results of the analysis and forecast of the high altitude atmosphere.Although the traditional dew point hygrometer has high accuracy,it is very expensive and has complex performance.Moreover,the humidity sensor with simple construction and low price cannot satisfy the accuracy requirement in atmosphere detection.Therefore,it is particularly important to design a humidity measurement system with high accuracy,good performance,simple structure and reasonable price.A high-altitude water vapor measurement system based on real-time operating system is proposed in this paper.In this system,STM32F103 is chosen as the main control chip.The probe of the dew point sensor is designed with the micro electro mechanical system and the AD7746 which is a high-precision and low-noise digital converter is used to measure the MEMS capacitance value.The structure of this part is very simple and can improve the accuracy of the system.In order to control the surface temperature of the MEMS capacitance,a peltier cooler is used to design the temperature control module of the system.Contrary to the the problem of limited adaptive parameters and slow response rate of traditional PID control algorithms,a PID control algorithm based on a BP neural network method is proposed to improve the self-adaptability and response rate and control the output power of the peltier cooler.The high-precision analog-to-digital converter AD7794 is used to measure the voltages of two PT100 temperature sensors.Then,the environment temperature and the dew point temperature can be measured by Corresponding formula of the resistance of PT100 and the temperature.After translating dew point temperature and the environment temperature to humidity using Go ff-Gratch Equation,atmospheric humidity is obtained to complete the design of this water vapor measurement system.The transplantation of FreeRTOS in the software design improves the efficiency and stability of tasks including the measurement,signal processing and communication.The use of the GPRS module can make the remote communication of data possible.So as to observe the data intuitively,the LabVIEW is used to design the user interface.Compared with a Michell OPTIDEW VISION dew point hygrometer,the measurement result shows that the accuracy of the system dew point temperature is able to reach to±0.2?and the accuracy of the system relative humidity is able to reach ±1.5%RH.In contrast to the traditional humidity sensors,the system has the advantages of simple structure,high precision and fast response speed.It can meet the measurement requirements of the high-altitude water vapor and is expected to be applied to the weather detection.