Effect of Annealing on Drift in Type S Thermocouples Below $$900\, ^{\circ }\hbox {C}$$ 900 ∘ C

Webster, E. S.

doi:10.1007/s10765-015-1910-7

Cited by 17 publications

(16 citation statements)

References 29 publications

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“…Large drifts of up to 0.5 °C are caused by the first two effects in parts of the thermocouple exposed to temperatures between about 200 °C and 1000 °C. These effects have been individually observed by Bentley [39], Jahan and Ballico [40,41] and Webster [36].…”

Section: Resultsmentioning

confidence: 55%

“…Oxidation was facilitated by heat treatment in air at 900 °C and at 1400 °C, for durations between 10 h and 80 h. It was found that external oxidation occurred at both temperatures after heat treatment. On the surface of the 900 °C samples, rhodium oxide formed (rhodium oxide is known to dissociate above about 1140 °C [29][30][31][32][33][34][35][36]); neither rhodium oxide nor zirconium oxide formed a dense protective layer on the surface.…”

Section: Grain Growthmentioning

confidence: 99%

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Stability assessment of a new high strength, high temperature Type R and Type S thermocouple

Pearce

Tucker

Rawal

et al. 2020

Meas. Sci. Technol.

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Platinum-rhodium Type R and S thermocouples fail in service because of two main reasons: excessive grain growth in the platinum limb at high temperatures (causing wire breakage) and temperature drift, i.e. deviation of electromotive force (emf) generated over time because of deposition of rhodium oxide on the platinum limb, out of accepted industry tolerances. Finding a solution to the problem is challenging because of the contradictory requirements of strength and narrow permissible emf range: emf is extremely sensitive to any dopants or alloying elements that can be used to improve strength at high temperatures. Johnson Matthey has developed a new thermocouple wire (platinum limb) called 'HTX ™ ' by doping platinum with a small quantity of zirconium which is oxidised during processing to electrically neutral zirconium oxide. Zirconium oxide improves the high temperature strength of platinum wire by restricting the grain growth but does not significantly affect the emf. The result is a wire which has the potential to last many times longer at high temperatures (>1200 °C) than standard platinum wire, whilst still achieving Class 1 tolerance (i.e. ±1 °C at 1000 °C). It also improves the thermoelectric drift characteristics of the thermocouple by counteracting any reduction in emf due to rhodium contamination by an increase in emf as any remaining zirconium is converted to zirconium oxide. We describe an impartial long-term assessment (up to 1500 h) of the thermoelectric stability of the HTX ™ wire by exposure to high temperature with periodic in situ calibration using a Co-C (1324 °C) high temperature fixed point. This yields stability measurements with very high precision.

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Section: Resultsmentioning

confidence: 55%

Section: Grain Growthmentioning

confidence: 99%

Stability assessment of a new high strength, high temperature Type R and Type S thermocouple

Pearce

Tucker

Rawal

et al. 2020

Meas. Sci. Technol.

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“…This treatment is usually at a temperature well below the annealing temperature and is designed to optimise the crystallographic state of various thermocouple alloys, ensuring that changes at other temperatures are minimised. Thermal preconditioning has been shown to be of benefit for constantan (E−, J− and T−) nicrosil (N+) [26], chromel (E+ and K+) [15,[26][27][28] and some Pt-Rh alloys (R+ and S+) [29][30][31]. Experimental work on thermal preconditioning treatments for constantan (types J, E and T) is currently in progress.…”

Section: Annealing and Heat-treatmentmentioning

confidence: 99%

“…The best way to minimise this problem is by regular annealing or thermal preconditioning, which will restore the thermocouple to a state close to that at the time of calibration. For example, with regular annealing, the expanded uncertainties for types R and S can be kept to between 0.1 • C and 0.2 • C [31,34,35]. However, the high variability in composition of base-metal alloys makes general statements more challenging.…”

Section: Calibrationmentioning

confidence: 99%

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

Webster¹

2021

Meas. Sci. Technol.

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The reference functions and tables for base-metal thermocouples, which relate temperature and electro-motive-force, are specified by thermocouple type, rather than by alloy composition. The common thermocouple types—E, J, K, N, and T—are required to meet the specifications within defined tolerance bands; referred to as either limits-of-error (ASTM, US) or class (IEC, UK and Europe). In this requirement hides a fundamental problem: the tolerances are a manufacturing specification. Despite this, the tolerances are often used as a proxy for expected behaviour. However, these thermocouple types are subject to rapid and irreversible changes after short exposure times to modest temperatures. Thus, tolerance statements are poor predictors of in-use behaviour. This paper initially reviews the development of the base-metal thermocouples before identifying many of the metallurgical processes that lead to departures from the accepted tolerance bands. Focus is specifically given to the processes that occur in several type K and N thermocouples, which exemplify the changes common in the other base-metal thermocouples. From these results, it is shown that the use of traditional calibration techniques can be a futile exercise. Comparisons are then made between as-received thermocouples and those given thermal treatments, that have been designed to allow meaningful calibration while also inhibiting drift. These results show that thermal treatments and calibration are a practicable means to minimise drift over typical periods of use while offering small uncertainties, well within the span of manufacturing tolerances. Lastly it is suggested manufacturers give more information on the testing used to establish conformance with tables and reference functions and that they follow standardised testing procedures.

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“…This method is accurate because the thermocouple is in close contact with the measured object, but it will affect the temperature field distribution of the object. Moreover, the thermocouple is easily to damage or temperature drift at high temperatures [15], which brings difficulty to the operational control of the cracking process.…”

Section: Introductionmentioning

confidence: 99%

A Method for Measuring Tube Metal Temperature of Ethylene Cracking Furnace Tubes Based on Machine Learning and Neural Network

et al. 2019

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Temperature monitoring of the tube metal temperature (TMT) of cracking furnace tubes is essential to the normal production of ethylene. However, the existing infrared temperature measurement technology has certain defects in the accuracy of temperature measurement, the accuracy of temperature discrimination of overlapping furnace tubes and the technical cost. In view of this, this paper proposes a novel measurement and processing method. In this method, our team developed a new generation of intelligent temperature measurement devices for measuring TMT, and proposed an intelligent temperature processing algorithm based on machine learning and neural network running on this intelligent temperature measurement devices. This method not only realizes the automatic measurement of TMT, reduces the workload of operators, but also improves the accuracy of measuring TMT and the accuracy of overlapping tube identification. In addition, this method also reduces the technical cost of TMT measurement to some extent. Finally, by comparing the TMT data measured by different methods, it is proved that the proposed method has better performance level than other methods. INDEX TERMS Ethylene cracking furnace tubes, machine learning, neural network, embedded processor.

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Effect of Annealing on Drift in Type S Thermocouples Below $$900\, ^{\circ }\hbox {C}$$ 900 ∘ C

Cited by 17 publications

References 29 publications

Stability assessment of a new high strength, high temperature Type R and Type S thermocouple

Stability assessment of a new high strength, high temperature Type R and Type S thermocouple

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

A Method for Measuring Tube Metal Temperature of Ethylene Cracking Furnace Tubes Based on Machine Learning and Neural Network

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