A comprehensive survey of thermoelectric homogeneity of commonly used thermocouple types

Abstract

Thermocouples are widely used as temperature sensors in industry. The electromotive force generated by a thermocouple is produced in a temperature gradient and not at the thermocouple tip. This means that the thermoelectric inhomogeneity represents one of the most important contributions to the overall measurement uncertainty associated with thermocouples. To characterise this effect, and to provide some general recommendations concerning the magnitude of this contribution to use when formulating uncertainty analyses, a comprehensive literature survey has been performed. Significant information was found for Types K, N, R, S, B, Pt/Pd, Au/Pt and various other Pt/Rh thermocouples. In the case of Type K and N thermocouples, the survey has been augmented by a substantial amount of data based on calibrations of mineral-insulated, metal-sheathed thermocouple cable reels from thermocouple manufacturers. Some general conclusions are drawn and outline recommendations given concerning typical values for the uncertainty arising from thermoelectric inhomogeneity for the most widely used thermocouple types in the as-new state. It is stressed that these recommendations should only be heeded when individual homogeneity measurements are not possible. It is also stressed that the homogeneity can deteriorate rapidly during use, particularly for base metal thermocouples.

Comparative Investigation on the Quality of Sensitivity of Six Different Types of Thermocouples

“…Sensitivity of 6 types of thermocouples composed commonly with 9 types of metals is analyzed in accordance with 3 related factors such as metal type, magnetic field, and chemical composition, it is crucial theme to determine quality of sensitivity, because the quality of sensitivity will depend on these factors, and it becomes clear for each of temperature range and to kind of medium being measured, then this can give an illustration, then to determine values of sensitivity, because the factors have real effects on the final temperature measuring results, but it should be mentioned that they are susceptible and could be affected by any of mechanical damage, chemical environment, and heat treatment [15].…”

Base-metal thermocouple tolerances and their utility in real-world measurements

“…This variability in performance between thermocouples from different manufacturers and even between batches of the same nominal type and format, makes much of the published in situ data of limited utility. However, recently an aggregation of inhomogeneity data exhibiting this variability was published to provide some practical guidance to end-users on how to incorporate this effect in uncertainty assessments [25].…”

An FPGA-based dual-wavelength correlated imaging system with flexible frame rates for temperature distributions

“…Thermocouples are widely used due to their easy installation, reliable readings and economical cost [5][6][7][8]. However, the thermocouple is intrusively installed and distorts the flow in its vicinity and fails to work if the temperature varies dramatically due to its slow response [9]. If temperatures are required in cases of contactless installations and fast response, optical methods are usually utilized due to their merits of ultra-wide temperature range, high temporal resolution and nonintrusive installations * Author to whom any correspondence should be addressed.…”