A Comparison of Contemporary Gold Versus Platinum Thermocouples with NIST SRM 1749-Based Thermocouples and Reference Function

Fluke Calibration (formerly Hart Scientific) in American Fork, Utah, USA is a manufacturer of temperature calibration instruments. The company manufactured reference standard gold versus platinum (Au–Pt) thermocouples from 1992 to about 2002. Manufacturing was halted in 2002 because a trend of poor curve-fit results was observed in new batches of wire. After reviewing the possible sources of the problem, it was decided to sample wire from multiple manufacturers and investigate ways to make the curve-fit work better. This paper presents the results from the study of the wire and a characterization technique to help improve characterization of thermocouples made with lower purity wire. Calibration results from NIST SRM material and older Fluke thermocouples are included as well to provide a means of comparison of contemporary wire to NIST SRM era wire.