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TitleA schottky-diode model of the nonlinear insulation resistance in HTSPRTs-Part II: Detailed two- and three-wire measurements
Publication TypeJournal Article
Year of Publication2007
AuthorsYamazawa, K., Arai M., and White D.R.
JournalInternational Journal of Thermophysics
Pagination1855 - 1867
Date Published2007
ISSN0195928X (ISSN)
KeywordsElectric insulation, Electrical insulation, Fused silica, High temperature effects, Leakage effect, Platinum, Platinum resistance thermometer, Schottky barrier diodes, Semiconductor diodes, Thermometers
AbstractElectrical leakage is a significant factor in the uncertainty of temperature measurements employing high-temperature standard platinum-resistance thermometers, with effects as large as several millikelvin at the freezing point of silver (962°C). The insulation resistance also exhibits complex behavior that includes non-linearities, sensitivity to the electrical environment, and the generation of spurious voltages and currents. In an earlier article, it was suggested that the behavior is consistent with the existence of metal-semiconductor diodes, also known as Schottky-barrier or point-contact diodes, formed at the points of contact between platinum wire and fused-silica insulators supporting the platinum. In this article, we describe detailed measurements of the non-linear resistance of a fused-silica insulator supported by platinum wires. The discussion includes a detailed description of the measurement system, and the results of two experiments that show many of the features suggested by the metal-semiconductor-diode model. Observed features in the current-voltage measurements include an S-shaped feature characteristic of back-to-back diodes, temperature dependence of saturation currents consistent with thermionic emission, and a diode polarity consistent with silica being a p-type semiconductor. Some impacts of the model on thermometry practice are also noted. © 2007 Springer Science+Business Media, LLC.

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