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Broadband UV radiometers are widely used for measuring UV irradiance or radiant exposure in various areas of health, industry, and science, such as in weather aging of materials, semiconductor lithography, non-destructive testing, UV curing, catalytic process, environmental monitoring, atmospheric research, water purification, medical diagnostics and therapy, space-based astrophysical observations and other applications. The accuracy of measurement is influenced by many factors such as the characteristics of the radiometer, operating conditions, environmental conditions and the UV sources to be measured. Due to the lack of spectral resolving power, significant measurement errors may occur if the radiometer has poor quality. Five different calibration and traceability methods of UV radiometers were realized and analyzed at National Institute of Metrology (NIM), including absolute spectral irradiance method based on standard lamps, absolute spectral power responsivity method of detectors, absolute thermoelectric radiometer method, electrically calibrated pyroelectric radiometer method and method of comparing with the standard radiometer. The above methods were used to realize the irradiance responsivity of a broadband UVA meter independently. Compared to absolute spectral irradiance method based on standard lamps, relative deviation of these traceability methods are 0%, 0.18%, 2.50%, -3.04% and 4.11% respectively. Absolute spectral power responsivity method of detectors is adopted by the most national metrology institute to realize UV irradiance responsivity. The deviation of absolute thermoelectric radiometer method results from poor signal-to-noise of the combination of radiation source and a UV filter, near to the sensitivity limit of the absolute radiometer. The largest deviation of method of comparing with the standard radiometer comes from different response wavelength, different receiving area between the standard radiometer and the test radiometer. Spectral irradiance method based on standard lamps is the principal traceability method of NIM tracing to the national spectral irradiance primary standard directly. This method was proved by international comparison of "Irradiance Responsivity of UVA Detectors APMP PR-S1". The comparison results showed that the consistency between the NIMs' value and the international reference one is the best among the seven participants. On the basis of the above theories and methods, the uncertainty of broadband ultraviolet irradiance standard under the defined conditions was cut down to 2.0% (k=1) from 10% (k=1).

This paper mainly discusses the measuring and traceable methods of spectral irradiance and ultraviolet irradiance in order to advance the accuracy of the two quantities. The contents include: 1.The working principal of the primary standard apparatus of spectral irradiance and spectral radiance and the value transferring methods of spectral irradiance. 2. The traceable methods of ultraviolet irradiance to spectral irradiance primary standard apparatus. 3. Introduce the international comparison of spectral irradiance and the comparison of irradiance responsivity of UV detectors. 4. The influence factors that decrees measuring accuracy of UV radiometer and the capability evaluated methods. We put forward a fitting function of spectral irradiance of standard lamp and an optimizing method for parameters. The relative deviation of the fitting function is acceptable comparing to the uncertainty of national primary standard of spectral irradiance lamp. We also defined evaluated capabilities of UV radiometers to reflect the instrument condition and promote measuring accuracy.

Spectral irradiance scale of 250nm-400nm has been realized with the temperature of blackbody traced back to the eutectic fixed-points blackbody. Since the ITS-90 can only be extended to 2473 K and spectral irradiance of 250 nm-400nm requests that the blackbody be operated around 3000 K. The temperature determination of blackbody is calculated using the ratio of spectra radiance at working temperature and a temperature no more than 2473 K. In the experiment, a pyrometer is calibrated by the Pt-C and Re-C eutectic fixed-points blackbody. Accordingly, the measuring scope of the pyrometer can be extends to 2747 K, which is more close to the working temperature. On the other hand, high temperature blackbody BB3500M is first used as the primary standard of spectral irradiance at the National Institute of Metrology (NIM).

Bandwidth is an important specification for monochromator and spectrograph. It varies with different slit widths and wavelengths. In actual spectral measurement, it is usually need to know the bandwidth. In the case of a Czerny-Turner double monochromator, we measured its bandwidth in finite different wavelengths as well as slit widths. Bandwidth can be represented as a function of wavelength and slit width. After the experiment, we get bandwidth in some discrete wavelengths and slit widths, bandwidth in other wavelength and slit width can be computed through mathematical process of the data that already acquired.

Wavelength calibration is important for monochromator and spectrograph before accurate application. In the case of a Czerny-Turner double monochromator, work have been down to find out the relationship between slit widths and wavelength error. We do wavelength calibration in different widths of entrance and exit slits, then get wavelength error. The result shows that different widths of entrance slit and exit slit lead to different wavelength error, and wavelength error can be presented as a function of wavelength and slit widths through curve fitting. Thus, correction can be done by solving this function before accurate measurement.