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A validated physical model of the thermoelectric drift of Pt-Rh thermocouples above 1200 °C
Metrologia ( IF 2.4 ) Pub Date : 2020-01-30 , DOI: 10.1088/1681-7575/ab71b3
Jonathan V Pearce

Pt and Rh oxide vapour transport is thought to dominate the thermoelectric drift of Pt-Rh thermocouples above about 1200 °C. A simple model is presented which relates the electromotive force (emf) drift rate of Pt-Rh thermoelements to the vapour pressure of Pt and Rh oxides. The model assumes that the evaporation of these oxides gives rise to a continuously changing concentration of Pt and Rh, at different rates along the length of the wires, which causes a change in the Seebeck coefficient. The model has been tested by comparison with high precision measurements of the thermoelectric drift of a Pt-Rh thermocouple assembly consisting of five thermoelements, repeatedly exposed to the melting of a Co-C high temperature fixed point (1324 °C) for a total duration of 500 hours. By considering various thermocouples of different compositions, it is demonstrated that the calculated drift rate is proportional to the measured drift rate, which represents a validation of the model.

中文翻译:

Pt-Rh 热电偶在 1200 °C 以上的热电漂移的经过验证的物理模型

Pt 和 Rh 氧化物蒸汽传输被认为在 1200 °C 以上时主导 Pt-Rh 热电偶的热电漂移。提出了一个简单的模型,该模型将 Pt-Rh 热电元件的电动势 (emf) 漂移率与 Pt 和 Rh 氧化物的蒸气压联系起来。该模型假设这些氧化物的蒸发会导致 Pt 和 Rh 的浓度沿导线长度以不同的速率不断变化,这会导致塞贝克系数发生变化。该模型已通过与由五个热电偶组成的 Pt-Rh 热电偶组件的热电漂移的高精度测量进行比较,反复暴露于 Co-C 高温固定点 (1324 °C) 的熔化总持续时间500 小时。通过考虑不同成分的各种热电偶,
更新日期:2020-01-30
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