Research On Optical Fiber Humidity Sensor System Based On STM32F

Humidity plays an important role in nature,so the monitoring of environmental humidity is very important.The electronic humidity sensor is widely used because of its high accuracy and wide measuring range,but the sensitive elements are vulnerable to electromagnetic interference,high temperature and substances in the air,resulting in the sensor not working properly.Because the optical fiber humidity sensor has many unique advantages,such as electrical insulation,anti-electromagnetic interference,small size,light weight,can be made into any shape,high sensitivity,so the optical fiber humidity sensor has attracted people’s research interest.However,the current optical fiber humidity sensor is relatively large and expensive,which is difficult to be applied in specific scenarios.Aiming at the above problems of the humidity sensor,this paper designs an optical fiber humidity sensor based on STM32F4.SiO₂ film is used as the new cladding of the optical fiber,and TiO₂ film is used as the humidity sensitive material to cover the SiO₂ film.The optical fiber sensor system uses STM32F4 single chip microcomputer as the main controller,and with the optical fiber humidity sensor and other functional modules,it realizes the accurate measurement of relative humidity.The main research work of this paper is as follows:（1）SiO₂ thin films were prepared by sol gel method and improved Czochralski method,and TiO₂ thin films were prepared by hydrothermal method and improved Czochralski method.SiO₂ film and TiO₂ film have stable properties and are not easy to age and fall off.TiO₂ film has super hydrophilic property and smooth surface,which can not only quickly absorb water molecules in the air,but also make water molecules on the surface volatilize quickly.The optical fiber humidity sensor has a sensitivity of 27.87 lx/%RH and a fit of 0.996 in the range of15%～40%RH;In the range of 40%～95%RH,the sensitivity of the sensor is 9.33 lx/%RH,and the fitting degree is 0.995.The fiber optic humidity sensor has good stability and repeatability,with a response time of 26 s and a recovery time of 45 s,and a fast response speed.In the range of 20～55℃,the sensitivity of the sensor is 29.49 lx/℃,and the fit is 0.997.（2）STM32F4 is used as the master controller,and BH1750,DHT11,ESP8266 and optical fiber humidity sensors are selected to design the optical fiber humidity sensor system.The optical fiber humidity sensor system quickly detects the relative humidity of the surrounding environment at a time interval of 1 second,and displays the temperature,humidity,and illumination information on the TFT LCD screen and sends it to the cloud server.After installing the server APP or logging in to the server on the smart phone,users can view the specific information of the measurement environment in real time.（3）When measuring the relative humidity of the environment,the change of the output light intensity of the optical fiber humidity sensor caused by the temperature change is eliminated to make the measured relative humidity value more accurate.Design the sensor structure and debug the program.The relative humidity measurement error of the optical fiber humidity sensor system is less than±2%RH.