Multiplicative Comparator of Spectral Radiances

The Process of Realization of the IPTS above 1337.58K and Performance of the Comparator

Abstract

The multiplicative comparator of spectral radiances built at the NRLM, was used to realize the International Practical Temperature Scale of 1968 (IPTS-68) above the gold point 1337.58K.
The comparator enables one to realize the condition corresponding to the equality L_x=L_y+L_z where L_x, L_y and L_z are the spectral radiances of radiation sources TL_x, TL_y and TL_z, respectively. This comparator makes it possible to multiply serially the spectral radiance 2ⁿ·L_Au, where L_Au is the spectral radiance of the blackbody of the gold point, through repetition L_x=2^n-1·L_Au+2^n-1·L_Au, which means the condition of L_y=L_z=2^n-1·L_Au. With the comparator, the temperature scale above 1337.58K is realized by this process of multiplication.
The precision of the comparator is ±7mK in transferring the spectral radiance of the gold point blackbody to that of the strip lamp and ±16mK in multiplying the spectral radiance serially by the factor of two.