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A Performance Assessment of Current Formulations of Bare-Wire and Mineral-Insulated-Metal-Sheathed Type N Thermocouples
International Journal of Thermophysics ( IF 2.5 ) Pub Date : 2021-04-03 , DOI: 10.1007/s10765-021-02831-y
Emile Webster

The Type N thermocouple, at its introduction in the early 1980s, was intended to radically improve base-metal thermocouple measurements and would render other base-metal types obsolete, or so it was claimed. Almost 40 years on, Type K persists in being the thermocouple of choice, despite adequate opportunity for the uptake of Type N. The reasons for this may be many; however, recent research at is showing Type N, at least at low temperatures, is not nearly as stable as early claims made out. This study reports on the inhomogeneities in Type N thermoelements, which develop as a function of temperature and time in a selection of mineral-insulated-metal-sheath (MIMS) and bare-wire samples sourced from a range of manufacturers. Measurements were made using a linear-gradient furnace and high-resolution homogeneity scanner. It was found that Type N thermocouples, in both the bare-wire and MIMS format, are susceptible to significant deviations in Seebeck coefficient from the reference functions at temperatures between 100 °C and 950 °C. In fact, use at temperatures below 500 °C can result in measurement errors equal to or worse than for equivalently specified Type K. Consequently, the benefits of using as-supplied Type N, in terms of accuracy and longevity, are only fully realized at temperatures greater than 900 °C. Despite these findings, additional experiments revealed drift rates can be reduced by about a factor of four if thermal preconditioning between 600 °C and 900 °C is used on MIMS Type N, which is similar to the improvements seen for thermally preconditioned MIMS Type K.



中文翻译:

裸线和矿物绝缘金属护套N型热电偶当前配方的性能评估

N型热电偶于1980年代初问世,其目的是从根本上改善贱金属热电偶的测量,并淘汰其他贱金属类型。尽管有足够的机会吸收N型,但将近40年以来,K型仍然是首选的热电偶。然而,最近的研究表明,至少在低温下,N型不如早期的宣称那样稳定。这项研究报告了N型热电偶的不均匀性,这些不均匀性随温度和时间的变化而发展,这些热电偶是从一系列制造商那里选择的矿物绝缘金属护套(MIMS)和裸线样品的选择。使用线性梯度炉和高分辨率均质扫描仪进行测量。已经发现,裸线和MIMS格式的N型热电偶在100°C至950°C的温度下都容易因参考系数的Seebeck系数而出现明显偏差。实际上,在低于500°C的温度下使用可能会导致测量误差等于或大于同等规定的TypeK。因此,就准确性和寿命而言,仅在完全满足以下条件的情况下使用提供的Type N的好处:温度高于900°C。尽管有这些发现,但另外的实验表明,如果在N型MIMS上使用600°C至900°C的热预处理,则漂移率可以降低约四倍,这类似于对K型热预处理的MIMS的改进。在100°C至950°C之间的温度下,Seebeck系数与参考函数的显着偏差非常容易。实际上,在低于500°C的温度下使用可能会导致测量误差等于或大于同等规定的TypeK。因此,就准确性和寿命而言,仅在完全满足以下条件的情况下使用提供的Type N的好处:温度高于900°C。尽管有这些发现,但另外的实验表明,如果在N型MIMS上使用600°C至900°C的热预处理,则漂移率可以降低约四倍,这类似于对K型热预处理的MIMS的改进。在100°C至950°C之间的温度下,Seebeck系数与参考函数的显着偏差非常容易。实际上,在低于500°C的温度下使用可能会导致测量误差等于或大于同等规定的TypeK。因此,就准确性和寿命而言,仅在完全满足以下条件的情况下使用提供的Type N的好处:温度高于900°C。尽管有这些发现,但另外的实验表明,如果在N型MIMS上使用600°C至900°C的热预处理,则漂移率可以降低约四倍,这类似于对K型热预处理的MIMS的改进。在低于500°C的温度下使用可能会导致测量误差等于或大于同等指定的K型。因此,就准确度和寿命而言,仅在高于50°C的温度下才能充分利用提供的N型所带来的好处。 900℃。尽管有这些发现,但另外的实验表明,如果在N型MIMS上使用600°C至900°C的热预处理,则漂移率可以降低约四倍,这类似于对K型热预处理的MIMS的改进。在低于500°C的温度下使用可能会导致测量误差等于或大于同等指定的K型。因此,就准确度和寿命而言,仅在高于50°C的温度下才能充分利用提供的N型所带来的好处。 900℃。尽管有这些发现,但另外的实验表明,如果在N型MIMS上使用600°C至900°C的热预处理,则漂移率可以降低约四倍,这类似于对K型热预处理的MIMS的改进。

更新日期:2021-04-04
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