At the PTB radiometric scales are compared which are based on electrodynamics (electron storage ring BESSY), on thermodynamics (black body of known temperature T90 of the International Temperature Scale) and on a thermal detector in combination with the electrical substitution principle (cryogenic radiometer). The uncertainty contributions of the different input parameters for establishing the independent radiometric scales are analysed in detail. According to this analysis spectral radiant powers in the visible are realized or expected to be realized (black body) with uncertainties (1 σ level) of 0,10% (BESSY), of 0,07% (black body, λ>650 nm) and of 0,007% (cryogenic radiometer). Filter radiometers calibrated at the three independent primary standards are used as transfer instruments for the comparison. The measured values of the responsivities of the filter radiometers are estimated to be uncertain by 0,11% (BESSY), 0,08% (black body, λ>650 nm), and 0,03% (cryogenic radiometer). Preliminary experimental results of the comparison between BESSY and the cryogenic radiometer are in agreement with the uncertainty analysis.
At the Physikalisch-Technische Bundesanstalt filter radiometers are used for the comparison of three primary radiometric standards, an electron storage ring, a black body of known temperature and a cryogenic radiometer. The calibration of the filter radiometers is performed in a two-step process. First, a trap detector is calibrated at the cryogenic radiometer at discrete laser lines. In the second step, this trap detector is used to calibrate the filter radiometers at a spectral comparator. Applying a correction for stray light, the responsivities of the filter radiometers can be measured over a dynamic range of more than eight decades in the wavelength range 420 nm to 1200 nm. To overcome drift effects of the interference filters, the filter radiometers were calibrated every night before and after an application. Following this procedure the responsivity was measured with a relative uncertainty of less than 5 × 10-4 at the 1σ level.
At the Physikalisch-Technische Bundesanstalt (PTB) silicon diode-based narrow-band interference filter radiometers (FR) are used for the radiometric determination of thermodynamic temperatures. To extend the temperature range down to 400 °C, the centre wavelength of the FRs was shifted from the visible to the near infrared (900 nm, 1000 nm and 1595 nm). An improved calibration procedure is presented which achieves relative uncertainties for the spectral responsivity of the FRs of the order of 10−4, by taking into consideration the increased temperature coefficient of the spectral responsivity and the nonlinearity of the silicon detectors when operated in the near infrared wavelength region.
The Physikalisch-Technische Bundesanstalt (PTB) has developed a spectral comparator facility for accurate spectral radiance measurements. As a primary standard source, a high-temperature black body (HTBB) is operated in the temperature range 1500 K to 3200 K. The black-body temperature is determined by two methods: monochromatic radiation thermometry relative to the freezing point of gold; and absolute radiometry with filter radiometers calibrated against a cryogenic radiometer. For these purposes, the HTBB is operated in radiance and irradiance modes at the same time. This paper presents an uncertainty analysis of the new spectral radiance scale embodied by gas-filled tungsten strip lamps from 220 nm to 2500 nm. Such lamps are currently used as transfer standards for the Consultative Committee for Photometry and Radiometry (CCPR) comparison of spectral radiance (CCPR-S1).
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