Behavior of Triple-Point-of-Water Cells for Different Sizes of the Ice Mantle

The effect of differences in the amount of ice mantle on the realization temperature of the triple point of water (TPW) was investigated. Three TPW cells were used in the experiment as the TPW cell under test. These TPW cells were manufactured at different times. An ice mantle was prepared for each cell, and the amount of these ice mantles was changed when the ice mantle was re-prepared. Comparison measurements were carried out between a standard TPW cell and the three cells under test, and the temperature difference was measured. As a result, although an identical TPW cell was used, a change in the temperature difference was observed when the amount of ice mantle was different. In the case of the TPW cell that was manufactured 30 years ago, the observed temperature change was larger than 0.1 mK. It is considered that the principal cause is the dissolution of glass elements from the TPW cell.     

液氮冻制冰套法对水三相点温度的影响

介绍了液氮作为冷却剂在水三相点容器内冻制冰套的方法。利用该方法同时在两个不同真空度的水三相点容器内分别冻制冰套。通过实验，研究了此方法对所复现的水三相点温度的影响。实验结果表明：冻制过程中产生的应力以及开始生成的小冰晶引起水三相点温度偏低；并且，其对水三相点温度的影响随着水三相点容器内真空度的降低而增大。随着应力慢慢消除，小冰晶逐渐长大为大冰晶，所复现的水三相点值逐渐回升并趋于稳定。因此，为了高精度复现和准确测量水三相点，采用该冻制方法时，必须将冰套老化至少5天以后，才可以消除其对水三相点温度的影响。     

金属外壳水三相点容器

水三相点是ITS-90国际温标中最重要的定义固定点,其复现不确定度是传递到整个温标的.目前,通常采用不同的冻制方法在硼硅玻璃或石英水三相点容器内冻制均匀的冰套来复现水三相点.冻制过程中,由于在水三相点容器内生成冰桥,会造成容器的破裂.为了解决此难题,研制了金属外壳水三相点容器,利用高纯水自发相变原理,在液体槽内自动冻制...     

高准确度水三相点容器

水三相点的高精度复现及准确测量是保证国际温标ITS-90实施的关键。水三相点容器内高纯水的同位素组成会影响复现的水三相点温度值。为了提高水三相点复现水平,减小氢氧同位素的影响,研制了带有氢氧同位素分析的石英及硼硅玻璃高准确度水三相点容器。为了评价容器的性能,开展了硼硅玻璃和石英水三相点容器的比对。实验结果表明:同位素修正前,石英玻璃和硼硅玻璃水三相点容器复现的水三相点在0.058mK范围内一致;同位素修正之后,容器之间的差异在0.017mK范围内一致。采用高准确度水三相点容器复现水三相点的扩展不确定度为0.066mK(k=2)。     

Construction of Sodium Heat-Pipe Furnaces and the Isothermal Characteristics of the Furnaces

Due to an excellent temperature flattening ability, annular sodium heat pipes operating from 500 °C to 1200 °C have been widely used as liners for isothermal furnaces to provide uniform and stable temperature zones. In order to develop the capabilities to fabricate liquid-metal heat pipes, an apparatus for fabricating sodium heat pipes was set up at the National Institute of Metrology (NIM), China. In this paper, the newly developed fabrication apparatus, the detailed procedures for manufacturing sodium heat pipes, the sodium heat pipes, the constructed furnaces for realizing the aluminum freezing point, and their isothermal characteristics are described. The experimental results showed that the biggest temperature differences within 150 mm from the bottom of the thermometer well in an aluminum point cell placed in the sodium heat-pipe furnaces were better than 15 mK, when the temperatures of the furnaces were controlled at approximately 657 °C.     

4种不同水源的水三相点容器的比对

为了研究水源对水三相点温度的影响,采用4种不同的水源并按照相同的制作工艺研制高质量的水三相点容器.同时,将这些容器进行了比对实验.比对结果表明:这些不同水源的水三相点容器复现的水三相点值在±0.02 mK范围内一致.故推断出水源对水三相点温度的影响很小.     

The Impact of Isotopic Concentration,Impurities, and Cell Aging on the Water Triple-Point Temperature

In 2005, the National Institutes of Standards and Technology (NIST) and Fluke’s Hart Scientific Division initiated a study to validate the isotopic correction algorithm applied to the realization temperature of triple point of water (TPW) cells. Additionally, the study quantified the impact of water sample impurities on the TPW cell realization temperature. For this study, eight TPW cells containing water of the same nominal isotopic concentration as Vienna Standard Mean Ocean Water (VSMOW) were used. Five of the cells were manufactured with fused-quartz envelopes and the remaining three with borosilicate envelopes. One TPW cell of each type was uniquely designed so that water samples could be periodically removed to analyze the isotopic composition and to monitor any changes in water purity with time and thereby correlate changes in composition with changes in realization temperature. The borosilicate TPW cells gave an average drift of −13 μK · yr⁻¹ and the more stable fused-quartz TPW cells gave an average drift of −2 μK · yr⁻¹.     

Analysis of the Comparison of TPW Realizations in Europe in Light of CCT Recommendation 2 (CI-2005)

Three comparisons of different triple-point-of-water (TPW) realizations in Europe have been organized under the auspices of EUROMET (EUROMET Projects 278, 549, and 714). Thirty European national metrology institutes were involved in these three comparisons that took place from 1994 to 2005. The aim of these successive projects was to assess the uncertainties associated with the practical realization of the triple point of water in Europe. Fifty-four TPW local cells were compared to a traveling standard cell (ref 679) circulated with an isothermal enclosure. The same equipment was used for the three projects, and LNE-INM regularly checked the stability of the TPW standard cell. Recently, LNE-INM has devoted efforts to bring the French standard at the triple point of water into close agreement with CIPM Recommendation 2 (CI-2005). The isotopic fractionation between water and ice when the cell is in use was experimentally studied. Several new TPW cells delivered by the manufacturer with water samples were added to our batch of reference cells. A French laboratory analyzed the isotopic compositions of these samples. These actions allow the French national definition of temperature at the triple point of water to be changed. A new temperature was associated with TPW cell 679 in agreement with the CIPM recommendation. In this presentation, the latest TPW cell measurements carried out by LNE-INM are presented. The results from EUROMET Projects 278, 549, and 714 are investigated in light of these changes.     

Realization of the Triple Point of Water in Metallic Sealed Cells at the LNE-INM/CNAM: A Progress Report

A miniature metallic cell for the water triple point (TPW, temperature 273.16 K) was developed for capsule-type thermometer calibrations for realizations with adiabatic calorimetry techniques. The LNE-INM/Cnam previously developed a copper cell for the water triple point and the techniques for cleaning, filling, and sealing. On the basis of previous work, a new copper cell prototype for the TPW was developed and filled at the LNE-INM/Cnam. Measurements were performed using an appropriate calorimeter and a comparison block containing several thermometers. Preliminary results show a scatter of the temperatures measured at the phase transition of the order of 0.2 mK when measurements are repeated over a short-term period (1 month). A positive drift in the phase transition temperature of about 30μK·month⁻¹ was observed over several months. Studies are in progress to improve the cell, to reduce the reproducibility uncertainty to less than 0.1 mK and to have a phase transition with better temporal stability.     

Characterization of High-Temperature Platinum Resistance Thermometers at Silver Point

Thermal cycling tests have been conducted on various types of high-temperature standard platinum resistance thermometers (HTSPRTs) that are commercially available at present. The investigated HTSPRTs have nominal resistance values at the triple point of water (TPW) of 0.25 \(\Omega \), 0.6 \(\Omega \), 2.5 \(\Omega \), and 3 \(\Omega \). They vary in terms of the platinum wiring on their sensor supports (frames) and the support materials, their protective sheaths and their sealing materials. Ten HTSPRTs were evaluated with regard to their stability during use at silver-point temperature or above. This evaluation included a thermal cycling test following various setup patterns, which indicated that each HTSPRT has its own preferred pattern. The stability test results for eight of ten HTSPRTs during four silver-point realizations, based on this pattern, yielded a maximum discrepancy in the resistance ratio of within \(\pm 6\,\hbox {mK}\). The maximum resistance discrepancy at TPW was \(\pm 2.7\,\hbox {mK}\).     

VSMOW Triple Point of Water Cells: Borosilicate versus Fused-Quartz

To investigate an ideal container material for the triple point of water (TPW) cell and to reduce the influence to the triple-point temperature, due to the deviation of the isotopic composition of the water, both borosilicate and fused-quartz glass shelled TPW cells with isotopic composition substantially matching that of Vienna Standard Mean Ocean Water (VSMOW) were developed and tested. Through a specially designed manufacturing system, the isotopic composition, δD and δ¹⁸ O, of the water in the TPW cell could be controlled within ±10‰ (per mil) and ±1.5‰, respectively, resulting in control of the isotopic temperature correction to better than ± 8 μK. Through an ampoule attached to the cell, the isotopic composition of the water in the cell could be individually analyzed . After manufacture, the initial triple-point temperatures of the two types of cell were measured and compared to assess the quality of the cells and manufacturing process. Cells fabricated with the new system agree within 50 μK. Two innovatively designed borosilicate and fused-quartz TPW cells were made, each with six attached ampoules. One ampoule was removed every 6 months to track any changes in purity of the water over time.     

Quasi-Adiabatic Investigations of Lead in Indium

The use of melting or freezing temperatures of high-purity substances as thermometric fixed points requires a knowledge of the binary phase diagrams of these substances and remaining impurities at very small impurity concentrations. In this paper, a calorimetric apparatus for the measurement of the change in liquidus temperature of fixed-point metals due to dissolved impurities at quasi-adiabatic conditions is presented. This approach combines advantages of the fixed-point method and adiabatic calorimetry. It is more efficient for the screening of a range of impurity concentrations than a fixed-point cell, requires less constructional and experimental expenditure compared with an adiabatic calorimeter, but provides similar small uncertainties on the millikelvin level. Measurements were carried out to determine the influence of lead on the melting temperature of indium at mass fractions up to 6.93 %. The results are in very good agreement with previous measurements by means of slim fixed-point cells in the Physikalisch-Technische Bundesanstalt and confirm a minimum of the freezing point of \(-\) 178 mK at a mass fraction of about 3.7 %. It was demonstrated that this setup allows the investigation of binary phase diagrams with uncertainties less than 8 mK.     

Effect of Impurities on the Triple Point of Water: Experiments with Doped Cells at Different Liquid Fractions

Recent international comparisons showed that there is still room for improvement in triple point of water (TPW) realization uncertainty. Large groups of cells manufactured, maintained and measured in similar conditions still show a spread in the realized TPW temperature that is larger than the best measurement uncertainties (25 µK). One cause is the time-dependent concentration of dissolved impurities in water. The origin of such impurities is the glass/quartz envelope dissolution during a cell lifetime. The effect is a difference in the triple point temperature proportional to the impurities concentration. In order to measure this temperature difference and to investigate the effect of different types of impurities, we manufactured doped cells with different concentrations of silicon (Si), boron (B), sodium (Na) and potassium (K), the glass main chemical components. To identify any influence of the filling process, two completely independent manufacturing procedures were followed in two different laboratories, both national metrology institutes (VSL, Netherlands and UME, Turkey). Cells glass and filling water were also different while the doping materials were identical. Measuring the temperature difference as a function of the liquid fraction is a method to obtain information about impurities concentrations in TPW. Only cells doped with 1 µmol·mol^?1 B, Na and K proved to be suitable for measurements at different liquid fractions. We present here the results with related uncertainties and discuss the critical points in this experimental approach.     

An Experimental Investigation of the Long-Term Stability of Triple-Point-of-Water Cells

Contamination of triple-point-of-water (TPW) cells by the chemical components of the borosilicate glass that contains the water is now widely recognized as the principal contributor to long-term drift of the cell temperature. To add to the available experimental data, a comparison of 24 TPW cells of various ages (from 10 years to 59 years), manufacturers (NRC, Jarrett, Isotech), and materials (borosilicate glass and fused quartz) was undertaken in 2013. Twelve cells from this group were compared to one another in 1997. By comparing the current inter-cell temperature differences to those determined 16 years earlier, it was found that some cells have remained stable, others have become colder (as might be expected from ongoing dissolution of the glass), and one or two show an apparent increase in temperature that seems anomalous. Also included among the 24 cells are five cells of borosilicate glass and five of fused quartz that were purchased 10 years ago. By comparing the relative temperature differences among this group of borosilcate and fused-quartz-encapsulated cells to the values obtained when they were last compared 6 years ago, it was found that the average temperature of the borosilcate group of cells decreases by \(-6\,\upmu \mathrm{K}\,{\cdot }\,\mathrm{year}^{-1}\,({\pm }2\,\upmu \mathrm{K}\,{\cdot }\,\mathrm{year}^{-1})\) , in reasonable agreement with an average drift of \(-4\,\upmu \mathrm{K}\,{\cdot }\,\mathrm{year}^{-1}\) suggested 12 years ago. It was concluded that fused quartz is the superior container for TPW cells.     

Method for Compensating Heat Flux Errors in Mini-TPW Cell Measurements

Small triple-point-of-water cells (mini-TPW) are used in laboratories to monitor the stability of PRTs. Compared with a standard TPW cell, heat flow in the thermometer well usually disturbs the apparent equilibrium temperature to a larger extent in a mini-TPW cell due to its smaller dimensions. In this paper, the heat flow effect is studied on the basis of experimental data. Special attention is paid to the thermal conduction along a thin thermometer probe and to the self-heating of the probe. A new method for compensating the error due to the heat flow is presented. It is shown that the compensated results are in good agreement with results obtained with standard TPW cells. The determined differences were well within the estimated expanded uncertainty of 2 mK (k = 2). The heat flow effect was studied experimentally by controlling the temperature of the upper part of a PRT inserted in a mini-TPW cell. Also, the effect of different fillings of the measurement well of the cell was studied. Without the compensation, thin metal-sheathed PRTs (1.6 and 2.2 mm) indicated 3 to 9 mK differences between mini-TPW and standard TPW cells.     

Comparison Measurements of Infrared Ear Thermometers Against Three Types of Blackbody Sources

Body temperature is a basic vital sign of the human body, and the use of infrared ear thermometers for medical diagnosis and health management on human bodies has been widespread nowadays. To gain credibility and confidence in the usage of IR ear thermometers, a standard blackbody source (BBS) with a calibration traceable to ITS-90 is necessitated. Three types of cavity-shaped blackbodies (designated BBC-A, BBC-E, and BBC-J) vertically immersed in a temperature-controlled stirred water bath were developed at the Center for Measurement Standards (CMS) as standard BBSs to calibrate and verify 14 commercial IR ear thermometers produced by six manufacturers. The basic structure of each cavity was designed based on the informative examples recommended in ASTM E-1965, EN 12470-5, and JIS T 4207 standards. The temperature of the blackbody cavity shall be represented by the water temperature near the bottom of the cavity that is measured using an immersed platinum resistance thermometer (PRT) for which the calibration is traceable to our national standard and with an uncertainty no greater than 0.03 °C (k = 2). The water bath was evaluated using the PRT to be stable within ±3.5 mK over 1 h and uniform within ±1.1 mK. Three types of BBSs were compared and analyzed utilizing two IR ear thermometers of 0.01 °C resolution as well as the statistical technique of analysis of variance (ANOVA). On the contrary, IR ear thermometers were tested and verified against three BBSs at three blackbody temperatures of 35.5 °C, 37 °C, and 41 °C. The analysis results of ANOVA showed that there is no significant temperature difference among three different structured blackbodies, and the average measured radiance temperature of three BBSs at 35.5 °C, 37 °C, and 41 °C were within 0.026 °C, 0.024 °C, and 0.027 °C of each other. Three among fourteen IR ear thermometers tested were outside of the 0.2 °C MPE (maximum permissible error) recommended by ASTM E-1965, EN 12470-5, or JIS T 4207 standards while BBC-A and BBC-E were used; however, four were outside of MPE requirement when BBC-J was used.     

Calibration of Radiation Thermometers and Blackbodies in the Temperature Range from 160 ��C to 420 ��C

The NMIJ has established a new calibration facility consisting of a 1.6??m radiation thermometer and three fixed-point blackbodies of indium (156.5985 °C), tin (231.928 °C), and zinc (419.527 °C) in the temperature range from 160 °C to 420 °C. The expanded uncertainties (k = 2) of the fixed-point blackbodies are estimated to be 28 mK for the In point, 22 mK for the Sn point, and 32 mK for the Zn point. The expanded uncertainties in the temperature scale of the 1.6??m radiation thermometer are estimated to be 40 mK to 77 mK. When this standard is used to calibrate devices under test to be used in industry, uncertainties (k = 2) of 61 mK for the In point, 67 mK for the Sn point, and 99 mK for the Zn point, 91 mK to 136 mK for a 1.6??m radiation thermometer, and 73 mK to 116 mK for a variable-temperature blackbody can be achieved.     

Thermal Characteristics of a Sealed Glass-Water Heat Pipe from 0?��C to 60?��C

Investigations into the thermal characteristics of glass-water heat pipes from 0 °C to 60 °C were carried out at the National Institute of Metrology (NIM), China. In this paper, studies on a glass-water heat pipe with four thermometer wells are described. The experimental results indicated that the temperature stability and uniformity of the thermometer well of the glass-water heat pipes are within several tenths of a millikelvin when the heat pipes are immersed in a constant-temperature liquid bath, since they have a highly effective thermal conductivity. They are able to maintain a constant temperature by the absorption or liberation of the latent heat of evaporation to attenuate temperature fluctuations of the surroundings. Also, above 0 °C to 30 °C, the temperature stability of the thermometer well of the glass-water heat pipe is better than 0.1 mK for approximately 16 h. The maximum temperature differences among the thermometer wells are less than 5.5 mK when the water heat pipes operate in the range from 0 °C to 60 °C. Therefore, water heat pipes are very promising to improve the performance of liquid baths and to accurately calibrate thermometers by comparison.     

Design and Validation of the MBW Standard Humidity Generators

MBW Calibration AG (MBW) is the Designated Institute (DI) for humidity appointed by the Federal Institute of Metrology, METAS. MBW currently offers calibration and measurement capabilities (CMC) for frost/dew-point hygrometers by comparison with precision chilled-mirror transfer standards that have been calibrated using the primary standards of leading European National Metrology Institutes or DI. The design, construction and validation of two standard humidity generators to be used as the Swiss national standards for the primary realization of frost/dew-point temperature in the range from ? 90 °C to + 95 °C are presented and discussed. The generators are operated as continuous flow “single-pressure” generators in the range from ? 80 °C to ? 10 °C with saturation over ice and from 0.5 °C to + 95 °C with saturation over water. Additionally, they are used in “two-pressure” mode for saturation over ice down to frost-point temperatures of ? 90 °C and down to ? 20 °C for saturation over water. The main saturators of both generators have been designed to fit in commercially available calibration baths with either ethanol or distilled water as the heat transfer fluid for saturator temperatures below and above 0 °C, respectively. Saturator temperature is measured using standard platinum resistance thermometers and a purpose-built precision thermometer. Pressure measurements are taken with gauge pressure transducers and a separate barometric sensor, to reduce the influence of the atmospheric pressure on the measurement of the pressure ratio and make full use of the correlation of pressure measurements and enhancement factors when operating in two-pressure mode. A totally automated pre-saturation and flow control system facilitates the calibration of state-of-the-art chilled-mirror transfer for standards without manual readjustment of the generated flowrate to ensure a constant volumetric flow at the conditions of the mirror. The uncertainty budget leading to the CMC for frost/dew-point temperature realization is presented in the context of the experimental validation performed. The results in the overlapping range of both generators are presented and used as further evidence of the saturation efficiency of both standards.     

Comparative Study of Pt/Pd and Pt–Rh/Pt Thermocouples

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.