Studies of instruments for measuring radiant energy in absolute value: an absolute thermopile

Abstract

I. Introduction 504 II. Apparatus and methods 1. The radiometer 2 Construction of the receivers 506 3. Thermopile and galvanometer 4. Water-cooled shutter and diaphragm 5. The radiator 6. The assembled apparatus 7. Method of making observations 8. Method of reduction of data 520 9. Corrections for diffuse reflection from the receiver 10. Accuracy attainable III. Experimental Data Receiver No. 1 Receiver No. 2 Receiver No. 3 Receiver No. 4 Receiver No. 5 Receiver No. 6 Receiver No. 7 Receiver No. 8 Receiver No. 9 Receiver No. 10 Receiver No. 11 Receiver No. 12 • Receiver No. 13 ,.

The Absolute Measurement of Radiant Power

“…Absolute thermopile. (Coblentz and Emerson, 1916) Based on its unfavorable assessment of absolute radiometers, the NBS proceeded to base its radiometric scale, first, on the radiant exitance of a blackbody according to the Stefan-Boltzmann law and, later, on the radiance of a blackbody as given by Planck's law (Coblentz and Stair, 1933;Kostkowski et al, 1970).…”

“…After a long period in which the U.S. NBS had concentrated solely on blackbody sources as the basis for its radiometric scale, the first absolute radiometers since Coblentz's (1916) instruments were developed at the NBS over the period 1968-1971 by Geist (1971). The main aim of the program was the creation of instruments that could be employed to realize, maintain, and transfer a scale of spectral irradiance.…”

“…It was established in 1932 after the introduction of an improved water-flow pyrheliometer based on the electri cal-substitution principle, that the original scale was in error by about 2.5 % (Drummond, 1970). Coblentz and Emerson (1916) conducted an intensive study of many variants of their absolute radiometer, which basically consisted of a black ened strip of metal in front of a bismuth-silver thermopile with a continuous receiving surface of tin. As there was only one detector element, the absolute radiometer was uncompensated.…”

The candela and photometric and radiometric measurements

“…ESRs have been in use for 75 years or more, and their history and development have been described by Hengstberger in considerable detail [ 16 ]. ESR technology was pioneered by Coblentz at NBS during the early part of this century [ 17 ]. He developed a number of radiometers and used them for diverse purposes in photometry and radiometry, including an early measurement of the Stefan-Boltzmann constant [ 18 ].…”