A versatile combined primary standard of the USSR has been established at VNIIOFI for the realization of radiometric units. The standard is based on two black bodies, operable at temperatures from 400 to 3000 K, and an absolute radiometer. Units of both spectral and broadband quantities are reproduced within the 0,2 pm to 25 pm range. A black-body radiator made of niobium carbide and graphite is used over the temperature range of 1500-3000 K, while that for the lower temperatures from 400 to 1200K is a heat-pipe with a sodium heattransfer medium. In order to determine the thermodynamic temperature T of the high-temperature black body, relative values of radiant flux P, ( T ) and spectral radiance Le, (ii, 7;) at several temperatures are found. The method allows realization of radiometric and photometric quantities irrespective of the International Practical Temperature Scale (IPTS-68). The absolute radiometer used is of a special design and has a control system capable of maintaining the conical receiving cavity at constant temperature throughout the measurement process. The absolute radiometer is intended to realize radiometric units as well as to measure the spectral sensitivity of radiation receivers.

A method of constructing the standard for the newly defined luminous intensity unit, the candela, in the USSR is described. The standard is based on a non-selective radiometer/black-body (BB) combination. The temperature of the radiating cavity of the BB is obtained by measuring spectral and integral components of radiation at two different temperatures. The radiometer conversion coefficient is not measured by a substituting winding, but with the help of the BB according to the Stefan-Boltzmann law. The relative spectral sensitivity of the radiometer is modified by the function V (λ) by means of a liquid filter. The unit of luminous intensity is then transferred by the photometer to the light-intensity-measuring lamps.The standard has been metrologically certified and the (relative) uncertainty of reproduction was found to be 4 × 10-3.

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A high-precision absolute radiometer with a thermally stabilized cavity as receiving element has been designed for use in solar irradiance measurements. The State Special Standard of the Solar Irradiance Unit has been built on the basis of the developed absolute radiometer. The Standard also includes the sun tracking system and the system for automatic thermal stabilization and information processing, comprising a built-in microcalculator which calculates the irradiance according to the input program. During metrological certification of the Standard, main error sources have been analysed and the non-excluded systematic and accidental errors of the irradiance-unit realization have been determined. The total error of the Standard does not exceed 0.3%. Beginning in 1984 the Standard has been taking part in a comparison with the Å 212 pyrheliometer and other Soviet and foreign standards. In 1986 it took part in the international comparison of absolute radiometers and standard pyrheliometers of socialist countries. The results of the comparisons proved the high metrological quality of this Standard based on an absolute radiometer.

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