Research On Humidity Source In Metrological Verification

The application of humidity is wide ranging from the initial meteorological measurement and grain storage to the production of industry(including electronics,machinery,automobile,textile,etc.),agricultural planting,medicine industry and HVAC industry,and then to many areas such as power generation and power transformation,national defense,military field and aerospace industry.Humidity has become an indispensable environmental parameter in human life.With the progress of science and technology,the humidity measurement has been from the original hair moisture meter to dry and wet bulb hygrometer,dew point hygrometer,and now widely used electrical hygrometer(including electric resistance hygrometer and electric capacity hygrometer,such as lithium chloride hygrometer and the ceramic humidity sensor,and etc.),and optical hygrometer,microwave hygrometer.Periodic calibration and verification need to be carried on to assess whether these temperature and hygrometers is qualified.Due to the huge quantity,miscellaneous categories and exponential growth of number,the verification of hygrometer is heavy in legal metrology department.So the legal metrology department needs to heighten the humidity source's performance,and then improve the verification efficiency.This project takes the humidity source used in calibration and verification is as the research object.Aim at the control problem of old humidity source,transforming humidity source in order to improve humidity source's performance.According to the indexes in calibration specification JJF1564-2016 Calibration Specification for Temperature and Humidity Standard Box,based on the original mechanical structure,this project upgraded the humidity source(Parameter Generation & Control Inc.)which could not meet the calibration specification.Starting with the principle of making gas with fixed humidity,meeting the requirements of the technical indicators is the ultimate goal,the project analyzed and designed the structure of the humidity source system and the control method of control system.On the basis of the selection of the key device precision and the controller resolution,the electrical principle is designed to complete the construction of the humidity source.The control algorithm of humidity in the humidity source is mainly studied in this project.Based on the principle of two-temperature method and the saturated vapor pressure equation,a humidity control algorithm using saturated gas dew point as the core is proposed.Because the model of heat and moisture transfer is too complex to bring it into the humidity control algorithm,so that the control of dew point temperature control is simplified to the control of air temperature difference and spray water temperature,in this project.The high accuracy cold mirror dew point instrument is used to calibrate the humidity control accuracy of the humidity source,and a large number of experimental data are used to correct the humidity control algorithm,so as to achieve high precision control.After heightening the humidity source,the humidity source was calibrated by using the multi-channel humidity measuring device,and the uncertainty of the technical parameters was evaluated.The result showed that the reconstructed humidity source meets the requirement of metrological verification.