Research Of Humidity Sensor Based On STM8S Single-chip Microcomputer And Its Calibration-check System

Based on the analog humidity sensor we developed in our laboratory last year, weresearched a new high precision digital humidity sensor with the function of temperaturesoftware compensation and on-line calibration. Meanwhile, we also developed acalibration and check system based on LabVIEW software to calibrate and check ourhumidity sensor. The main content of this dissertation are as follow:For our analog humidity sensors encounter the problem with short precision, amultivibrator based on a high speed voltage comparator named TLV3501was introducedto convert humidity capacitance signal to frequency signal. The humidity sensor designedin this paper used STM8S as its MCU to process the frequency signal. Because of thesedesigns, the precision of our digital humidity sensor reached±2%RH while the precisionof the analog humidity sensor was just±5%RH.The analog humidity sensor also met the problem with unfavorable adjustment of theoutput range and the difficulty in recalibrating the sensor. To solve this problem, afunction named online calibration was researched in the digital humidity sensor. First, anonline calibration module made by LabVIEW software was built.Then we used thismodule to calculate the fitting coefficient. In the end, we sent the fitting coefficient to theMCU through USART serial port. This function was used to calibration our sample, andsuccessfully made the humidity deviation fell from12.1%RH before calibration to1.9%RH after calibration at25℃.For temperature can influence the humidity measurement a lot, this thesis usedmultiple regression equation to give a software temperature compensation to the digitalhumidity sensor. At10℃and40℃,the maximum humidity deviation changed from3%RH before compensation to1.7%RH after compensation. This dissertation also introduced the design of the check module based on LabVIEWsoftware. The module used Advantech USB4711A data acquisition card to collect thevoltage signal. The data acquisition card can collect15road voltage signals at a time, andits resolution is12bits. The module can check the humidity sensor for testing to see ifthe output humidity value within the prescribed scope. The detection value can be stored.