PRESENT STATE OF THE COMPARISON BETWEEN RADIOMETRIC SCALES BASED ON 3PRIMARY STANDARDS

At the PTB radiometric scales are compared which are based on electrod ynamics (electron storage ring BESSY), on thermodynamics (black body o f known temperature T90 of the international Temperature Scale) and on a thermal detector in combination with the electrical substitution pr inciple (cryogenic radiometer). The uncertainty contributions of the d ifferent input parameters for establishing the independent radiometric scales are analysed in detail. According to this analysis spectral ra diant powers in the visible are realized or expected to be realized (b lack body) with uncertainties (1 sigma level) of 0,10 % (BESSY), of 0, 07 % (black body, lambda > 650 nm) and of 0,007 % (cryogenic radiomete r). Filter radiometers calibrated at the three independent primary sta ndards are used as transfer instruments for the comparison. The measur ed values of the responsivities of the filter radiometers are estimate d to be uncertain by 0,11 % (BESSY), 0,08 % (black body, lambda > 650 nm), and 0,03 % (cryogenic radiometer). Preliminary experimental resul ts of the comparison between BESSY and the cryogenic radiometer are in agreement with the uncertainty analysis.