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Comparative study of Pt/Pd and Pt-Rh/Pt thermocouples.

Ongrai, O; Pearce, J V; Machin, G; Sweeney, S J* (2010) Comparative study of Pt/Pd and Pt-Rh/Pt thermocouples. Int. J. Thermophysics, 31 (8-9). pp. 1506-1516.

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The Pt/Pd thermocouple has demonstrated superior thermoelectric drift and homogeneity performance over conventional Pt/Pt-Rh thermocouples. Here we present a systematic comparison of the drift and homogeneity performance of Pt/Pd and Type R thermocouples by ageing the thermocouples at 1350 °C for a total of 500 hours and measuring the performance at regular intervals during this time.
The thermocouples studied were 1 Pt/Pd thermocouple, 1 Type R thermocouple, and 1 'special' Type R thermocouple which was given the same preparatory annealing treatment as the Pt/Pd thermocouple prior to use. The thermoelectric stability of each thermocouple was measured at the freezing point of silver (961.78 °C) and the melting point of Co-C eutectic (1324.29 °C).
The long term drift of the Pt/Pd thermocouple was around 50 mK after the first 100 hours ageing at 1350 oC, followed by a further 25 mK over the subsequent 400 hours ageing. This drift performance was an order of magnitude lower than the two Type R thermocouples. The Type R thermocouple which was given the 'special' preparatory treatment was slightly more stable than the conventional Type R.
The thermoelectric homogeneity of the thermocouples was also measured at regular intervals by a dedicated movable localised heat source, which demonstrated the evolution of the thermoelectric homogeneity profile with aging.

Item Type: Article
Keywords: Nobel metal thermocouples, high temperature measurement
Subjects: Engineering Measurements
Engineering Measurements > Thermal
Identification number/DOI: 10.1007/s10765-010-0782-0
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/4858

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