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.     

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.     

System for Realizing the Triple Point of Mercury to Calibrate Industrial-Type Platinum Resistance Thermometers

Most platinum resistance thermometers (PRTs) sent to CENAM for calibration are of the industrial type (IPRT). The cells used to calibrate both standard PRTs (SPRTs) and IPRTs form part of the national standard of temperature. In order to reduce their use, we built a set of fixed-point cells, furnaces, and baths to calibrate IPRTs using fixed points, including an apparatus and cells to reproduce the Hg triple point. To realize the triple point of mercury (TP-Hg), an apparatus that operates from room temperature to  − 45 ^◦C using a CENAM-constructed heat pipe was designed and built. With the heat pipe, it is unnecessary to use a recirculation bath to provide a temperature-controlled environment, the temperature gradient is reduced, and the system is more efficient because its thermal mass is reduced. In this way, it is possible to reproduce the TP-Hg for long periods of time to facilitate IPRT calibration, using cells of smaller size than is conventional and without using expensive liquid baths. The system was tested with cells having 400 g and 800 g of mercury, and a reproducibility of about 0.1 mK was obtained.     

Automated Realization of the Triple Point of Water Using the Mush Method

In order to investigate mechanisms of phase transitions of supercooled water in a triple-point-of-water (TPW) cell when a mush method was used to create an ice mantle, an automated apparatus using small TPW cells was developed to obtain the TPW. In this article, the design principle, the apparatus, and the procedure for an automated formation of ice mantles in small TPW cells are described. Supercooled water in small TPW cells spontaneously transformed into uniform metastable dendritic crystals throughout the cells at supercoolings ranging from 5.85 °C to 8.77 °C and then changed into stable hexagonal closed-packed cellular crystals, forming an outer ice mantle from the outside inward. Some pertinent explanations based on thermodynamic solidification theory were used to describe the phase transition process in the mush method. In addition, the experimental results indicated that the realized temperatures of water in the small TPW cells were in good agreement within 0.1 mK approximately 6 h after the initial spontaneous crystallization had occurred. Finally, the small TPW cells (s/n 008 and s/n 001) were directly compared with a conventional TPW cell (s/n NIM-1-211); the temperature differences between the small TPW cells and the regular TPW cell were less than 0.21 mK.     

套管对水三相点的影响研究

为了研究套管对水三相点的影响,研制了计阱内径分别为16 mm和18 mm的水三相点容器以及直径为15.5 mm的套管。通过在计阱内加套管和不加套管,并利用准确度为0.02×10^-6的交流比较仪电桥测量标准铂电阻温度计在计阱内的电阻值,比较不同直径水三相点容器内套管对水三相点的影响。实验结果表明:实验中套管对水三相点值的影响小于30 μK,且在相同的测量条件下,套管的直径与水三相点容器温度计阱的内径越接近,套管对水三相点值的影响越小。     

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...     

Thermal Hysteresis in Thin-Film Platinum Resistance Thermometers

Thin-film platinum resistance thermometers (PRTs) are generally manufactured using the deposition of a thin platinum film on an alumina substrate and a laser-trimming method. Because of the strong adhesion between the platinum thin film and the alumina substrate, the PRTs inevitably have strain over the operating temperature range. This causes anomalies and instabilities in the resistance versus temperature characteristics (R?CT). The most prominent and observable effect of thermally induced strain is the thermal hysteresis in the R?CT characteristics. Thermal hysteresis is one of the main uncertainty factors in the calibration of industrial platinum resistance thermometers in laboratories. The thermal hysteresis for 30 thin-film PRTs was measured in the range of 0 °C to 500 °C in 100 °C steps. The thermal hysteresis was measured repeatedly using the same process, and the hysteresis decreased drastically with the repeated measurements. The thermal hysteresis was distributed from 16 mK to 156 mK for all sensors, and the lowest hysteresis was 1 mK to 11 mK in the test temperature range.     

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)。     

一种高精度薄膜铂电阻温度计测量迟滞性的研究

为了研究热迟滞性对工业铂电阻温度计测量不确定度的影响,选取了8支高精度铂电阻温度计进行实验。在-50～150℃内,选择3个温度区间,采用两种标准方法(IEC 60751,ASTM E644)测量水三相点(0.01℃)和所选温度范围内的中间点的迟滞性变化。实验结果表明:4支薄膜铂电阻温度计在两种标准方法测量下,随着温度区间跨度增大,热迟滞性影响增大,IEC 60751标准方法测量的热迟滞性最大值为14.2mK,ASTM E644标准方法测量的热迟滞性最大值为20.5mK;选取4支铂丝铂电阻温度计在温度范围为-50～150℃测量时,IEC 60751和ASTM E644标准方法测量的热迟滞性数据最大值分别为1.1mK和0.9mK;铂丝铂电阻温度计热迟滞性明显小于薄膜铂电阻温度计。     

Implementing a New Group of TPW Cells as National Standard: Impact on Calibration Services

The definition of the kelvin is based on the triple-point temperature of highly pure water having the isotopic composition of ocean water (more specifically, the isotopic composition is equivalent to that of VSMOW). Belgian national metrology realizes the triple point of water (TPW) as the mean of temperatures measured in three sealed cells. In order to take into account the isotopic composition effect on TPW temperature, the ensemble of cells was replaced in 2006. Three new cells, with isotopic analysis of the contained water, were bought from different manufacturers. The new group of cells was compared to the old TPW national realization in order to quantify the effect of moving towards a new reference. Two different standard thermometers were used in all the cells to take 10 daily measurements on two different ice mantles. The measured resistances were corrected for hydrostatic head, self-heating, and isotopic composition (when available) before calculating the difference. A difference of about 87 μK was found between the old and the new national references. This difference is transferred to customers’ thermometers and cells through calibrations, and the change has to be documented in each new calibration certificate. An additional consequence of the new ensemble cell implementation is the significant reduction in the spread of deviations of individual cells from the mean temperature. The maximum difference between two cells of the ensemble is 96 μK for the old reference cells and 46 μK for the new reference cells corrected for isotopic composition effects.     

Calibration by Comparison of Platinum Resistance Thermometers Using Slow Resistance Bridges

Platinum resistance thermometers (PRTs) are calibrated at the highest level in fixed points, as specified in the International Temperature Scale of 1990 (ITS-90). However, in order to reduce cost and time, platinum resistance thermometers can also be calibrated by comparison. In the temperature range from ?100 °C to 300 °C, it is possible to achieve uncertainties as small as 5 mK. A PRT is calibrated by comparison by comparing its resistance reading with the temperature reading of a reference thermometer, placed at the same temperature inside the temperature-controlled calibration medium. The reference thermometer is commonly also a resistance thermometer, so the intrinsic measurement problem is the simultaneous measurement of two resistances. Four methods that perform this measurement are presented in this article. A special emphasis is given to the measurement with slow bridges. Slow bridges are not able to produce a stable resistance reading within 20 s after the connection of the PRT, so they are often considered to be unsuitable for calibration by comparison of PRTs. To overcome this problem, a special method that directly measures the ratio between the reference PRT and PRT under calibration is presented and analyzed. The analysis and measurement results proved that this method and consequently the slow resistance bridges are capable of performing calibration by comparison of PRTs at least at the same level as the conventional methods.     

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.     

Effect of platinum oxidation on the characteristics of standard platinum resistance thermometers

Platinum oxidation in PTS-10 and PTS-25 standard platinum resistance thermometers has been studied. The experimental results show that heat treatment of a thermometer at 100–300°C can increase its resistance at the triple point of water by the equivalent of 1.5 mK. A procedure for calibration in the range 0–450°C is recommended. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 41–44, July, 1996.     

An intercomparison of a Cu nuclear susceptibility thermometer and an Sn99 mösbauer effect thermometer between 6 mK and 1 K

The cold-absorber Sn¹¹⁹ Mössbauer effect thermometer discussed by Parshin et al, has been compared with the steady-field Cu nuclear magnetic susceptibility thermometer. The Curie constant of the Cu thermometer was also determined from simultaneous measurements using a ballistic CMN thermometer. The sensors were installed in the mixing chamber of a dilution refrigerator capable of producing temperatures below 6 mK in the single cycle mode. The absorber never cooled below 7.8 mK due to heat leaks. Good consistency and reproducibility were established between 10 and 100 mK.     

Construction and use of a pulsed copper nuclear magnetic resonance thermometer

A pulsed nuclear magnetic resonance thermometer, constructed for temperature measurements below 0.5 K, is described. The nuclear free precession signal of copper nuclei is recorded with a gated low noise amplifier and with a phase sensitive detector gated to integrate the signal over an adjustable number of periods. The physical significance of the signal is discussed. A comparison of the resonance thermometer against a slurry type cerium magnesium nitrate (CMN) thermometer for the temperature region 10 mK to 100 mK is presented. The deviation Δ = T_NMR − T_CMN, representing the departure of the CMN thermometer from a Curie law behaviour, was measured as (0.5 ± 0.2) mK. In experiments with a nuclear refrigeration cryostat the resonance thermometer was calibrated against a nuclear orientation thermometer which provided an independent absolute temperature standard. At the low temperature end, from 1 mK to 10 mK, the linearity of the thermometer in T⁻¹ was confirmed by measurements of the nuclear spin-lattice relaxation time.     

The specific heat capacity and thermal conductivity of normal liquid3He

By observing the diffusion of a heat pulse along a 10-cm column of normal liquid³He with the aid of two vibrating wire thermometers, it has been possible to measure the heat capacityC and thermal conductivityK of the liquid in the temperature range fromT _C to 10 mK and at pressures of 0.21, 4.39, 9.97, 20.01, and 29.32 bar. By using a Pt NMR thermometer, an LCMN thermometer, and a³He melting curve thermometer calibrated using the melting curve given by Greywall in 1983, a temperature scale has been established and (1) it has been shown that this melting curve is consistent in the temperature range 5–22 mK with the Korringa law for the Pt thermometer with a Korringa constant of 29.8±0.2 sec mK, (2) departures have been observed from the Curie-Weiss law for LCMN at low temperatures, and (3) values of the superfluid transition temperature have been obtained that are about 4% lower than the Helsinki values. The measured heat capacities agree well with those of Greywall, but values ofKT are higher than those of Greywall and show more temperature dependence below 10 mK. The implications for the present results of the very different melting curve given by Greywall in 1985 are discussed in an Appendix.     

Heat capacity and thermal conductivity measurements down to 25 mk on samples of poor thermal diffusivity and small specific heat

A heat pulse technique is described with a permanent heat link to the cold sink used for the measurement of small heat capacities, such as vitreous dielectrics, down to 25 mK. Total heat capacities of the order of 5μJ K^?1 are measured below 50 mK with an accuracy of 5%. Two carbon resistor thermometers are used to avoid any systematic error.Thermal conductivity measurements are also performed in the same temperature range by the steady flow method. The accuracy of the carbon resistor thermometer calibration enables the measurement of 2 or 3 mK temperature gradients at 25 mK.     

Isotopic Correction of Water-Triple-Point Cells at NMIJ

The twenty-one participating laboratories in the international key comparison of water-triple-point cells (CCT-K7) can be classified into three groups: two laboratories that corrected the effect of the isotopic composition of water, four laboratories that had information on the isotopic composition but did not correct the effect, and the remaining laboratories that had no information. There were significant differences in the realized national standard for the triple point of water (TPW) between those laboratories that applied the isotopic correction and those that did not. The isotopic correction is now considered essential for the triple point of water. Since the National Metrology Institute of Japan (NMIJ) did not apply the isotopic correction and estimated large uncertainties at the time of the CCT-K7 comparison, we subsequently developed new cells for the TPW to improve the reliability and to reduce the uncertainty of the realization as a national reference. The isotopic compositions of seven cells were analyzed, and a chemical impurity analysis of one cell was performed. The good consistency among seven cells was shown in the results obtained when the isotopic correction was applied to the realized temperatures measured experimentally. The expanded uncertainty of the new national reference of NMIJ is estimated to be 49 μK (k = 2), and as a result of this improvement, the expanded uncertainty for calibrating a water-triple-point cell is 80 μK. The previous reference of NMIJ, reported in CCT-K7 to have an expanded uncertainty of 302 μK, is 42 μK lower than the new one. The new reference value is within the uncertainty of the previous national reference, and the new uncertainty is completely covered by the previous uncertainty. Furthermore, the new reference of NMIJ shows good agreement with the national references of the six laboratories able to apply isotopic corrects to their results for CCT-K7. These facts confirm the validity and the linkage to the CCT-K7 of both the previous and the new national references of NMIJ.     

Isotopic Composition of Water Used in Triple-Point Cells

Isotopic analysis of the water used in KRISS triple point of water (TPW) cells was performed by three separate laboratories. The δD and δ ¹⁸O isotopic composition of six ampoules, made from two TPW cells, were analyzed by isotope ratio mass spectrometers. The analysis data showed that δD and δ ¹⁸O were − 62.17‰ and − 9.41‰ for the KRISS-2002-Jan cell, and − 36.42‰ and − 4.08‰ for the KRISS-2005-Jun cell. The temperature deviation of the triple point of water for these cells calculated from Kiyosawa’s data and the definition of the TPW were + 45.07μK for the KRISS-2002-Jan cell, and + 25.49μK for the KRISS-2005-Jun cell. The KRISS TPW temperature was + 92μK higher than the CCT-K7 KCRV after correcting for the deviation of the isotopic composition from Vienna Standard Mean Ocean Water.     

Measurement technique for thermal conductivity of thin polymer films

We present a modified steady-state heat flow technique, which allows measuring the thermal conductivity of films applied on a substrate. The measurement technique with the here presented setup provides an accuracy (overestimation) of 5-10% for film thickness up to 100 μm. For thicker films a correction factor based on finite-element simulations has to be used or the geometry has to be adapted. The technique is validated with thin glass plates of known thermal conductivity. To demonstrate the application of the technique the thermal conductivity of a thin polymer film of fluorinated acrylate is determined as 0.19 ± 0.02 W/mK.