We report on technical advances and new results in noise thermometry at temperatures near the tin freezing point and the zinc freezing point using a Quantized Voltage Noise Source (QVNS). The temperatures are derived in a series of separate measurements comparing the spectral power density of QVNS synthesized noise with that of Johnson noise from a known resistance at both 505 K and 693 K. Reference noise is digitally synthesized so that the average power spectra of the QVNS match those of the thermal noise, resulting in power ratio spectra which are close to unity in the low-frequency limit. Three-parameter models are used to account for differences in impedance-related time constants. Direct comparison of noise temperatures to ITS-90 is achieved in a comparison furnace with standard platinum resistance thermometers. We report on the observed noise temperatures determined by operating the noise thermometer in both absolute and relative modes, and related statistics together with estimated uncertainties. The relative noise thermometry results are combined with results from other thermodynamic determinations at temperatures near the tin freezing point to calculate a value of T T90 =+4 +/- 18 mK for temperatures near the zinc freezing point. These new results achieve a lower uncertainty than that of our earlier efforts and we compare the present value of T T90 to other published determinations from noise thermometry and other methods.
Citation: International Journal of Thermophysics
Pub Type: Journals
ITS-90, Johnson Noise Thermometry, Synthesized Noise, Temperature