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TitleA schottky-diode model of the nonlinear insulation resistance effects in SPRTs-Part 1: Theory
Publication TypeJournal Article
Year of Publication2007
AuthorsWhite, D.R., Arai M., Bittar A., and Yamazawa K.
JournalInternational Journal of Thermophysics
Pagination1843 - 1854
Date Published2007
ISSN0195928X (ISSN)
KeywordsElectric conductivity, Fused silica, Insulation, Insulation breakdown, Platinum, Platinum thermometers, Schottky barrier diodes, Standard platinum resistance thermometers (SPRT), Temperature measurement, Thermometers
AbstractThe decreasing insulation resistance of standard platinum resistance thermometers (SPRT) above about 850 °C makes a major contribution to uncertainties in measured temperatures. In principle, the insulation breakdown ought to be easily modeled as a temperature-dependent shunt resistance depending principally on the insulator materials and dimensions. However, the phenomenon exhibits a complex nonlinear behavior that, to date, has defied explanation. The lack of an explanation is a major obstacle to improvements in SPRT design and to assessments of uncertainty caused by the insulation breakdown. This article suggests that the nonlinear effects are due to metal-semiconductor diodes, also known as Schottky-barrier or point-contact diodes, formed at the points of contact between the fused-silica insulators and the platinum of the SPRT sensing element and lead wires. The article presents an overview of the theory underlying Schottky diodes, shows that this model qualitatively explains the observations, and suggests practical experiments to verify the model. © 2007 Springer Science+Business Media, LLC.

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