A radiometric determination of the Stefan-Boltzmann constant and thermodynamic temperatures between -40 °C and +100 °C

Abstract

The total radiant exitance of a black body at the temperature of the triple point of water, T tp (273.16 K), and at a series of other temperatures in the range from about 233 K ( — 40 °C) to 373 K (100 °C), has been measured by using a cryogenic radiometer. From the measurements at T tp a value for the Stefan—Boltzmann constant or has been calculated: ( r = (5.66967 + 0.00076) x 10 -8 W m -2 K -4 . This is the first radiometric determination of or having an uncertainty comparable with that calculated directly from fundamental physical constants. This measured value differs from the calculated one by 13 parts in 10 5 , which is less than the combined standard deviations of the measured and calculated values. mbined standard deviations of the measured and calculated values. From the measurements of exitance at the other temperatures, values of the corresponding thermodynamic temperature T have been calculated by using Stefan’s fourth-power law. Since the temperature of the radiating black body was also measured by platinum resistance thermometers calibrated on IPTS-68, values of ( T — T 68 ) were obtained. These range from about — (5 + 1.6) mK at 20 °C to — (28 ±2.5) mK at 100 °C and + (5 + 1.5) mK at —40 °C. The results confirm to within a few millikelvins the departure of T 68 from T above 0 °C already discovered by gas thermometry and show that similar departures, but of opposite sign, exist down to the lowest temperature measured, — 40 °C. The uncertainties associated with these new values of T and ( T — T 68 ) are similar to those of the best gas thermometry.

Accurate radiometry from space: an essential tool for climate studies

“…Similar instruments were also used in the NMIs to establish primary radiometric scales. Quinn and Martin of the National Physical Laboratory (NPL) made a step change in the performance of this type of instrument through cooling to the temperature of liquid helium [14]. This cooling reduced many of the sources of uncertainty significantly, leading to more than a factor of 50 improvement in accuracy.…”

“…The cryogenic radiometer is an extension of the concepts of the electrical substitution radiometer (ESR), summarized in §2a(iii) [14,16], which were independently developed by the metrologists Ångström [46] and Kurlbaum [47]. Cooling the technology to cryogenic temperatures (<30 K) reduces uncertainty levels to less than 0.01 per cent (95% confidence) as first shown by NPL in the 1980s [14] due primarily to better equivalence between electrical and optical power and the ability to build a large cavity to absorb optical radiation while maintaining a reasonable sensitivity. Cryogenic radiometers are now the primary standard of choice for NMIs.…”

The Absolute Measurement of Radiant Power

“…Although the exact cause for the spread of the results was not identified, the major part of the blame was apportioned to the absolute detectors. However, more recent experience with measurements of the Stefan-Boltzmann constant Quinn and Martin, 1985) has shown the crucial importance of diffraction phenomena, especially with such a relatively longwavelength spectrum as that of a 1000°C blackbody. These could conceivably have accounted for a sizable portion of the observed scatter and the absolute radiometers developed at the NBS were perhaps not as unreliable as they seemed on the basis of these measurements.…”

“…In that case, however, the right-hand part of the Eq. (1.25) had to be multiplied by the current ratio 1 2 β\> Kurlbaum's highly regarded measurements of the Stefan-Boltzmann con stant, which were performed on blackbodies of 0 and 100°C (Kurlbaum, 1898), yielded a value of 5.32 χ 10" 8 Wm -2 K" 4 , which is about 6% lower than the best estimate of this constant in 1985 (Quinn and Martin, 1985). Determinations done before Kurlbaum by calorimetric methods had given values for the constant ranging between 4.23 and 5.06 χ 10" 8 Wm~2 K~4 (Kurlbaum, 1898 using a value for the electrothermal equivalent of 4.185W/ [gcal/s]).…”

A career at the National Physical Laboratory

“…The original drawing is now proudly framed in my study at home. 4 When we had finished the work on temperature measurements and the StefanBoltzmann constant, Terry Quinn and I reported the results in Philosophical Transactions of the Royal Society series A in 1985 (figures 1 and 2), 5 and I was transferred to the Radiometry Section. There I worked with Nigel Fox and continued to work on photodiodes and laser radiometry with the cryogenic radiometer.…”