| Dust measuring instrument is widely used in atmospheric environment monitoring and industrial dust monitoring.The accuracy of the results of dust air quality monitoring instrument is of great significance for environmental protection departments to announce the air pollution situation and evaluate the effect of environmental protection policies and measures,and even affect the credibility of government departments.The development of a measurement standard system for dust concentration detectors which can be used as a measurement standard is a powerful technical guarantee for the monitoring of atmospheric environment and the control of industrial dust emission in China.Quasi-value Traceability Technology is sampling flow traceability,which can only reflect the performance of dust sampling flow,and can not directly measure the main performance of the instrument.In this paper,taking the measurement and verification device of low dust concentration measuring instrument in the concentration range of 0-1000 mg / m3 as the research object,this paper discusses the origin and development background of this type of measuring instrument and its measurement standard device,establishes the theoretical foundation through the research status at home and abroad,expounds the structure and principle of this type of low concentration dust measurement standard,and simply analyzes a variety of traceability methods.In the aspect of test environment simulation,according to the different dust concentration,two kinds of dust generation and aerosol preparation devices based on fluidized bed and atomization spray were designed respectively,and corresponding PID control method was designed to control the flow of jet flow,fluidized bed and atomizer,which provided stable initial velocity of dust diffusion for the whole device.Through the force analysis of dust particles in the air flow field,the movement track of dust in the test air duct is studied.Aiming at the ultra-low concentration(0-50 mg / m3)and the low concentration(50-1000 mg / m3)dust environment,two kinds of dust dispersion devices,horizontal airflow diffusion and vertical gravity diffusion,are designed.The dynamic dust generation system and dust sensor array uniformity detection system are innovatively designed to solve the problem of uniformity distribution in the dust diffusion stage,and reduce the class B uncertainty caused by dust diffusion uniformity in the calculation of standard uncertainty.In the measurement standard detection section,based on the importance of direct traceability method,two traceability methods are introduced,and a more suitable mass volume traceability method is selected by comparative analysis and uncertainty analysis of measurement results.At the same time,the two kinds of aerosol preparation methods are analyzed,and different aerosol preparation methods are adopted for different concentration ranges,so as to make the measurement standard device more targeted for calibration and detection.After the aerosol particles are emitted successfully,the dust particles can move evenly through the design of dust collecting duct.The uniformity is controlled within 6%,and the repeatability of measurement results is controlled within 10%.A stable and uniform dust environment is formed on the test surface.On the basis of stable test environment,the standard dust concentration is obtained by calculating the mass difference before and after the sampling filter membrane and the sampling flow volume,and the uncertainty of the measurement results is evaluated,and the corresponding measurement uncertainty is less than 8%.The device has the advantages of high test precision,uniform and stable dust generation,and high detection automation.It can meet the measurement standard verification of most dust concentration meters at home and abroad,and provide scientific and reliable technical guarantee for the traceability of dust concentration measurement instruments in China.The paper has 38 figures,8 tables,and 93 references. |
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