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The performance of a simple, new design Au/Pt thermocouple developed by NMIA is assessed. This thermocouple is proposed as
a more accurate replacement, over the temperature range from 0 to 1,000°C, for the commonly used Type R and S industrial transfer
standards, in a robust form familiar to industrial calibration laboratories. Due to the significantly different thermal expansions
of the Au and Pt thermoelements, reported designs of the Au/Pt thermocouple incorporate a strain-relieving coil or bridge
at the thermocouple junction. As the strain relieving coil is mechanically delicate, these thermocouples are usually mounted
in a protective quartz tube assembly, like a standard platinum resistance thermometer (SPRT). Although providing uncertainties
at the mK level, they are more delicate than the commonly used Type R and S thermocouples. A new and simple design of the
Au/Pt thermocouple was developed in which the differential thermal expansion between Au and Pt is accommodated in the thermocouple
leads, facilitated by a special head design. The resulting thermocouple has the appearance and robustness of the traditional
Type R and S thermocouples, while retaining stability better than 10 mK up to 961°C. Three thermocouples of this design were
calibrated at fixed points and by comparison to SPRTs in a stirred salt bath. In order to assess possible impurity migration,
strain effects, and mechanical robustness, sequences of heat treatment up to a total of 500 h together with over 50 thermal
cycles from 900°C to ambient were performed. The effect of these treatments on the calibration was assessed, demonstrating
the sensors to be robust and stable to better than 10 mK. The effects on the measured inhomogeneity of the thermocouple were
assessed using the NMIA thermocouple scanning bath. 相似文献
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O. Ongrai J. V. Pearce G. Machin S. J. Sweeney 《International Journal of Thermophysics》2010,31(8-9):1506-1516
The Pt/Pd thermocouple has demonstrated superior thermoelectric drift and homogeneity performance over conventional Pt–Rh/Pt 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 h and measuring the performance at regular intervals during this time. The thermocouples studied were one Pt/Pd thermocouple, one Type R thermocouple and one ‘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 Ag (961.78 °C) and the melting point of Co–C eutectic (1324.29 °C). The thermoelectric homogeneity of the thermocouples was also measured. Two difference methods were used by withdrawing the thermocouple from the Ag cell and by moving a localized heat source along the thermocouple. The long-term drift of the Pt/Pd thermocouple was around 50 mK (Ag) and 65 mK (Co–C) after the first 100 h ageing at 1350 °C, followed by a further 25 mK (Ag) and 35 mK (Co–C) over the subsequent 400 h ageing. This drift performance and inhomogeneity were an order of magnitude lower than for the two Type R thermocouples. The Type R thermocouple which was given the ‘special’ preparatory treatment was about 50 % more stable than the conventional Type R thermocouple. 相似文献
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Cold-working of most thermocouples has a significant, direct impact on the Seebeck coefficient which can lead to regions of thermoelectric inhomogeneity and accelerated drift. Cold-working can occur during the wire swaging process, when winding the wire onto a bobbin, or during handling by the end user—either accidentally or deliberately. Swaging-induced cold-work in thermocouples, if uniformly applied, may result in a high level of homogeneity. However, on exposure to elevated temperatures, the subsequent recovery process from the cold-working can then result in significant drift, and this can in turn lead to erroneous temperature measurements, often in excess of the specified manufacturer tolerances. Several studies have investigated the effects of cold-work in Type K thermocouples usually by bending, or swaging. However, the amount of cold-work applied to the thermocouple is often difficult to quantify, as the mechanisms for applying the strains are typically nonlinear when applied in this fashion. A repeatable level of cold-working is applied to the different wires using a tensional loading apparatus to apply a known yield displacement to the thermoelements. The effects of thermal recovery from cold-working can then be accurately quantified as a function of temperature, using a linear gradient furnace and a high-resolution homogeneity scanner. Variation in these effects due to differing alloy compositions in Type K wire is also explored, which is obtained by sourcing wire from a selection of manufacturers. The information gathered in this way will inform users of Type K thermocouples about the potential consequences of varying levels of cold-working and its impact on the Seebeck coefficient at a range of temperatures between \(\sim 70\,^\circ \)C and \(600\,^\circ \)C. This study will also guide users on the temperatures required to rapidly alleviate the effects of cold-working using thermal annealing treatments. 相似文献
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Thermocouples are increasingly used in industry and research. For many industrial heating processes, particularly those carried
out at high temperatures, a thermocouple is the most convenient and simple instrument for temperature measurement. In some
instances, it is the only feasible method. The aim of this study is to select and recommend the best thermocouples from both
base and noble metals to users in industrial and scientific institutions. Different types of thermocouples and calibration
methods are described. From this work, the Nicrosil–Nisil thermocouple has been proposed as the best base metal thermocouple
and the Au/Pt thermocouple is the most recommended as a substandard up to 1,000 °C. 相似文献
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The Thermoelectric emfs of thermocouples formed by amorphous METGLAS 2826 (Fe40Ni40P14B6) and METGLAS 2826B (Fe29Ni49P14B6Si2) with standard thermocouple wires like copper, chromel, alumel, etc., were measured as a function of temperature between
−196° C and 30° C to assess their suitability as thermoelectric temperature sensors. Thermoelectric emfs generated by METGLAS
2826/Cu and METGLAS 2826B/Cu thermocouples at −196° C are about an order of magnitude smaller when compared to thermal emfs
of a standard copper/constantan thermocouple at the same temperature. 相似文献
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E. S. Webster 《International Journal of Thermophysics》2017,38(9):135
Type K thermocouples are the most commonly used thermocouple for industrial measurements because of their low cost, wide temperature range, and durability. As with all base-metal thermocouples, Type K is made to match a mathematical temperature-to-emf relationship and not a prescribed alloy formulation. Because different manufacturers use varying alloy formulations and manufacturing techniques, different Type K thermocouples exhibit a range of drift and hysteresis characteristics, largely due to ordering effects in the positive (K+) thermoelement. In this study, these effects are assessed in detail for temperatures below \(700\, {^{\circ }}\hbox {C}\) in the Type K wires from nine manufacturers. A linear gradient furnace and a high-resolution homogeneity scanner combined with the judicious use of annealing processes allow measurements that separately identify the effects of cold-work, ordering, and oxidation to be made. The results show most K+ alloys develop significant errors, but the magnitudes of the contributions of each process vary substantially between the different K+ wires. In practical applications, the measurement uncertainties achievable with Type K therefore depend not only on the wire formulation but also on the temperature, period of exposure, and, most importantly, the thermal treatments prior to use. 相似文献
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A. A. Ulanovskiy V. A. Medvedev S. N. Nenashev Yu. A. Sild M. S. Matveyev A. I. Pokhodun P. P. Oleynikov 《International Journal of Thermophysics》2010,31(8-9):1573-1582
In the temperature range (900 to 2800) K, there has been confirmed compliance with the existing national standards for thermocouple wires W5% Re/W20%Re (type A) produced in Russia. The homogeneity within a lot of wires was evaluated by measuring the emf deviations from the corresponding reference function of thermocouples constructed from the front and the rear sections of paired coils of wires. The diameter of the wires amounted to 0.35 mm and 0.5 mm. Stability indicators were thermal emf changes after annealing for 2 hours at 1773 K. It was found that the inhomogeneity of thermoelements did not exceed (4 to 5) K for paired wire coils with a thermoelectric stability within a temperature equivalent of (1.0 to 1.5) K. EMF deviations from the reference table values for the thermocouples investigated did not exceed 1 % in the temperature range of (900 to 2773) K. Such deviations meet the requirements of the new draft of IEC standards 60584-1 and 2. Thermocouples were calibrated in four laboratories by comparison with various standard temperature gauges (type B thermocouple, radiation pyrometer, standard specimens of thermoelements). Measurements were carried out under vacuum, argon, and hydrogen. Depending on the calibration method, the expanded uncertainty of the measurements at 1773 K varied from (2.8 to 8) K. 相似文献
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The aim of this paper is to create a method of built-in self-testing of thermocouples in situ. This aim is achieved by using the equivalent operating time of the thermocouple. The method does not require replacement of thermocouples from their operating place as it could be done during the operation of the thermocouples. The only necessary condition, that makes self-testing possible, is a constant measuring junction temperature during the procedure of self-testing. The determined equivalent operating time allows finding the place of a given thermocouple in the thermocouple’s drift model as well as in the model of thermoelectric inhomogeneity. 相似文献
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K. C. Sloneker 《International Journal of Thermophysics》2011,32(1-2):537-547
Very little if any current data is available for the life expectancy of very small diameter thermocouples operating at high temperatures, greater than 1000???C. Over the past 10?years significant changes in the supply stream of the materials used to manufacture base metal thermocouples have occurred. In many industrial applications, small diameter thermocouples are the only solution for high-temperature measurements. This study has been undertaken to assess the performance of small diameter magnesium oxide insulated metal sheathed thermocouple sensors at or above 1000???C. Three different American Society of Testing and Materials (ASTM) standard letter designation thermocouple types have been included in this study, Types E, K, and N. Inconel 600 and 316 stainless, for three different sizes, 0.5?mm, 1.0?mm, and 1.5?mm, have been tested for different thermocouple types. Each group of sensors was placed in an equalization block in air for a maximum of 500?h or until failure. The performance of 0.5?mm diameter thermocouples varies widely depending on the thermocouple type, sheath material, and test temperature. Larger diameter Type K and N thermocouples show very little drift up to 500?h at 1100???C. The data for each test was collected at 10?s intervals for the entire duration of the test. Data for the sensor drift and subsequent failure are presented. 相似文献
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根据实际使用中出现的问题,对各种实用的管道气流温度传感器的误差进行了计算,对电阻式和热电偶式温度传感器的误差原因作了定量分析。由于带密封罩的温度传感器在实际使用中存在着明显的缺点,建议今后使用热电偶测量飞机环控系统管道气流温度,并提出了一种实用热电偶温度传感器的结构形式,同时也介绍了如何减小由于热传导和热辐射引起的误差。 相似文献
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A simple thermocouple probe with tip diameter less than 10 μm has been developed for mapping temperature distribution on surfaces. The fabrication procedures of the thermocouple tip involve fixing a fine tungsten wire inside a glass capillary tube and coating the exposed tip with gold. We have successfully used the thermocouple tip to obtain a two-dimensional temperature map on the heatsink of a high-power light-emitting diode (LED), thus demonstrating this device as a low-cost alternative to expensive infrared cameras for near-field thermal imaging 相似文献
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Lianchao Sun Kevin J. Jakubenas James E. Crocker Shay Harrison Leon L. Shaw Harris L. Marcus 《Materials and Manufacturing Processes》1998,13(6):909-919
Fabrication of a SiC/C thermocouple embedded in an arbitrarily-shaped SiC macro-component has been demonstrated using an integrated Selective Area Laser Deposition (SALD) with the closely related Selective Area Laser Deposition Vapor Infiltration (SALDVI) process. SALD is used to make the embedded thermocouple devices in situ and SALDVI to fabricate the macro-components. The thermocouple elements, silicon carbide and carbon lines, and the electrical insulation layer, Si3N4, have been deposited from tetramethylsilane (TMS), acetylene, and a gas mixture of TMS and ammonia, respectively. It is found that the fabricated in situ thermocouples respond sensitively to temperature variation. Furthermore, the electric signal of the embedded thermocouple is very stable and reproducible in response to thermal cycling. This is not the case when the thermocouple is not embedded in the SiC matrix because of the oxidation of the thermocouple elements. 相似文献
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AMS2750标准规定了热处理过程热加工设备的高温测量要求,它包括温度传感器(一般指热电偶)、仪器、热加工设备、系统精度测试和温度均匀型测试五个部分。而热电偶技术要求是高温测量的最重要的内容,本文就热电偶的技术要求对NADCAP认证过程中以及日常使用维护中容易存在和忽视的问题进行了剖析。 相似文献
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An automated thermocouple calibration system 总被引:2,自引:0,他引:2
An automated thermocouple calibration system (ATCS) was developed for the unattended calibration of type-K thermocouples. This system operates from room temperature to 650°C and has been used for calibration of thermocouples in an eight-zone furnace system which may employ as many as 60 thermocouples simultaneously. It is highly efficient, allowing for the calibration of large numbers of thermocouples in significantly less time than required for manual calibrations. The system consists of a personal computer, a data acquisition/control unit, and a laboratory calibration furnace. The calibration furnace is a microprocessor-controlled multipurpose temperature calibrator with an accuracy of ±0.7°C. The computer software is menu-based for flexibility and ease of use. The user needs no programming experience to operate the system 相似文献