A Determination of the Ratio of the Zinc Freezing Point to the Tin Freezing Point by Noise Thermometry
Weston L. Tew, John Labenski, Samuel P. Benz, Sae Woo Nam, Paul D. Dresselhaus
We have used a Johnson-Noise Thermometer (JNT) with a Quantized Voltage Noise Source (QVNS) as a calculable reference to determine the ratio of temperatures near the Zn freezing point to those near the Sn freezing point. The temperatures are derived in a series of separate measurements comparing the synthesized noise power from the QVNS with that of Johnson noise from a known resistance. The synthesized noise power is digitally programmed to match the thermal noise powers at both temperatures and provides the principle means of scaling the temperatures. This produces a relatively flat spectrum for the ratio of spectral noise densities, which is close to unity in the low-frequency limit. The data are analyzed as relative spectral ratios over the 4.8 kHz to 450 kHz range averaged over a 3.2 kHz bandwidth. A three-parameter fit model is used to account for differences in time constants that are inherently temperature dependent. A drift effect is observed of approximately -6 microK/K per day in the results and an empirical correction is applied to yield a relative difference in temperature ratios of -11.5 microK/K 39 microK/K with respect to the ratio of temperatures assigned on the International Temperature Scale of 1990 (ITS-90). When these noise thermometry results are combined with results from acoustic gas thermometry at temperatures near the Sn freezing point, a value of T T90 = 7 mK 27 mK for the Zn freezing point is derived.
, Labenski, J.
, Benz, S.
, Nam, S.
and Dresselhaus, P.
A Determination of the Ratio of the Zinc Freezing Point to the Tin Freezing Point by Noise Thermometry, International Journal of Thermophysics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=830990
(Accessed October 23, 2021)