Research on nonlinear error test of solar radiation measuring instrument

Nonlinearity is an important parameter for judging the performance of the radiation instrument. As the laboratory equipment for testing solar radiation measuring instrument, the stability of solar simulator light source is crucial to nonlinearity testing. In this paper, a mesh attenuation method used for testing nonlinear error of solar radiometers is presented. Different mesh type attenuators with different apertures are designed, then these mesh type attenuators are used in light source of solar simulator separately, and the irradiance at different intensities can be obtained. According to this method, nonlinear errors of 15 sets FS-6S pyranometers are tested. And the results show that such 15 pyranometers reach the first class pyranometer level recommended by WMO and ISO. Moreover, the nonlinear error of CMP21 pyranometer is tested for twice, the result ±0.5% is consistent with the nonlinearity indicator given by the manufacturer, which validates the correctness of mesh attenuation method in testing nonlinear error of solar radiometers.