Research Of Thermal Analysis And Nonequivalence Of Solar Irradiance Absolute Radiometer

The sun as the Earth's most important external energy source,any of its tiny changes will cause changes in the Earth's radiation income and expenditure,and ultimately lead to the Earth's environment and climate change.So,it is important and necessary to set up the long-term,continuous,accurate monitoring work of solar irradiance in the world.The solar absolute radiometer is electrical substitution radiometer.After 50 years of development,it has become the main monitoring instrument for solar irradiance measurement.The instrument is a kind of pyroelectric infrared detector,which has the characteristics of high absorption rate and high precision.The working principle of the system is that the power of the incident light can be reproduced by the electric power which can be accurately measured by the photoelectric equivalence.In this paper,the structure and working principle of SIAR(Solar Irradiance Absolute Radiometer),which is developed by the CIOMP,are introduced.Based on the measured data of the total solar irradiance established in Davos,Switzerland,the ground datum of solar radiometer for solar radiation was established.Then,The uncertainty of the reference radiometer and the international comparative experiment requirements together determine the choice of solar absolute radiometer time constants.The thermal characteristics of the SIAR internal structure are of importance.Based on the actual structure of SIAR and measurement of Direct Solar Irradiance in Davos,this paper uses finite element method to analyze the thermal performance of SIAR.The results obtained provide the basis for the temperature response of the radiometer,which provides the guidance for the further optimization of the radiometer design and development.This paper also makes a detailed study on the photoelectric nonequivalence.It is found that the photoelectric nonequivalence of SIAR is mainly composed of the primary reflection of light beam,the different heating region and the heating position,as well as the thermal radiation of the shutter.The finite element method and the theoretical calculation method are used to measure and correct the solar irradiance measured.The result is close to the standard of the world radiation center.Finally,combined with the method of thermal analysis of SIAR,CIOMP developed a new generation of cryogenic absolute radiometer,which named ARCPR.According to the analysis,a new type of thermal structure is designed.A controlled heat sink is added in this structure,and a directly connection method was used to improve the stability of temperature of heat sink.