Triple Point Of Water Cells Research Articles

Supplementary comparison on a platinum resistance thermometer calibration from -70 °C to 250 °C

Main textThis supplementary comparison was about the calibration of platinum resistance thermometers in the range of -70 °C to 250 °C. Four laboratories participated in the comparison: Emirates Metrology Institute (EMI) from United Arab Emirates, SASO-NMCC from Saudi Arabia, QGOSM from Qatar and Tubitak UME from Türkiye. These Institutes are full or associated (Tubitak UME) members of the GULFMET Regional Metrology Organization.The pilot institute was Emirates Metrology Institute, who also provided the two transfer platinum resistance thermometers and monitor their stability during the comparison.The measurements of the comparison were performed between April 2019 and February 2021 and the circulation of the instruments was without problems, except for a delay of four months between the laboratories QGOSM and EMI due to the Coronavirus pandemic.The weighted mean of the measurements from all laboratories was used to produce the W ratios and R 0.01 reference values of the thermometers and no laboratory was excluded from this weighted mean. Note that this comparison is an RMO supplementary comparison, so the weighted mean values generated are used only as a baseline for reporting the results, and they have no particular meaning of reference values in the sense of the key comparisons.The results show a satisfactory agreement between the participating laboratories (|En| <1), except for two set-points: -35 °C and 100 °C, for one of the two transfer thermometers, for one of the laboratories. Combined expanded uncertainties for R 0.01 were equivalent to about 0.004 °C for the laboratories using water triple point cells as a reference, and 0.010 °C for QGOSM laboratory using ice point as reference. For the other measurement points, R values, were having equivalent combined expanded uncertainties ranging from 0.0060 °C to 0.010 °C for UME, 0.008 °C to 0.016 °C for EMI, 0.012 °C to 0.024 °C for SASO-NMCC and 0.014 °C to 0.054 °C for QGOSM. The mentioned uncertainties refer to the most stable of the transfer thermometers used in the comparison.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

A triple point of water cell-based fixed-point blackbody for radiation thermometry

The radiation temperature metrology above 150 °C relies heavily on the use of physical interpolation equations and known reference temperature (provided by solid–liquid phase transition of high-purity metals and metal-carbon eutectic alloys) fixed-point blackbodies. Recent achievements in thermal infrared detector technologies triggered the extension of the scale interpolation below this temperature down to 0 °C by using the reference temperatures provided by Sn, In, Ga fixed-points and ice-point, where the reference temperature of the later is dependent on external parameters. In this work, we demonstrate that the triple-point of water (TPW) based fixed-point blackbody is the metrologically grounded alternative to the ice-point. For this purpose, a fixed-point blackbody, incorporating only a cavity and large area TPW (LATPW) cell was designed, constructed, and validated for the precise calibration of radiation thermometers (RTs) and thermal cameras at the thermodynamic temperature of TPW. The conceptual design of the LATPW cells is similar to the ones used in contact thermometry, where a thermometer well of the cell is employed as a borehole for a cavity, where the cavity is easily detachable. Four different cavities (two different designs with aperture sizes of 40 mm and 50 mm) and three LATPW cells with two distinct well geometries were comparatively studied in several combinations. The largest absolute temperature difference observed between the primary level reference TPW cell (used in contact thermometry) and the LATPW cells is measured to be only 0.37 mK. Radiometric measurements demonstrate that all radiators maximally reflect the blackbody condition including emissivity close to unity, high uniformity across the aperture and high temporal stability. The simplicity of maintenance and easy in-field usage (only distilled water and dry ice are required) make the TPW blackbodies very versatile for the in-situ calibrations of RTs and thermal cameras, allowing its application in many areas including clinical environments.

No country for old borosilicate triple-point-of-water cells

Temperature calibration labs all around the world typically maintain a set of several triple-point-of-water (TPW) cells for regular measurements using the International Temperature Scale of 1990 (ITS-90). This set often includes more-than-10-year-old TPW cells made from a borosilicate glass. In this paper we summarize the problems with old borosilicate TPW cells, using the available literature data, the results of CCT.K7-2021 key comparison and NRC TPW measurements, and highlight the solution to these issues—vitreous-silica TPW cells. The latter have an exceptional long-term stability, as we demonstrate by using: (a) comparative measurements of the same-age, same-manufacturer vitreous-silica and borosilicate TPW cells at NRC in a period from 2007 to 2021, and (b) inductively coupled plasma-mass spectrometry (ICP-MS) analysis of impurities present in the 18 year-old vitreous-silica outlier, cell Q325. Remarkably, not only all NRC vitreous-silica TPW cells remained stable over a 15 years time period, unlike their borosilicate counterparts, but the amount of impurities in the ‘coldest’ cell Q325 (−31 μK from the intercomparison reference value) is comparable to that in the newly purchased vitreous-silica cells. We argue that the most accurate TPW measurements, such as for defining the national TPW references and for the international key comparisons, should rely exclusively on vitreous-silica TPW cells.

NRC measurement set-up and preparatory work for CCT-K7.2021 key comparison of triple-point-of-water cells

This paper describes the NRC measurement set-up and the preparatory work for the CCT-K7.2021 key comparison (KC) of triple-point-of-water (TPW) cells. The preparatory work at NRC (charged with piloting the KC) included a comprehensive testing of the measurement set-up, the definition of the new NRC national standard for the TPW temperature, and the evaluation of the uncertainty budgets relevant for this KC. The new NRC TPW national standard is composed of an ensemble of ten fused silica TPW cells, characterized in both their isotopic composition and impurity content. Three uncertainty budgets were evaluated, corresponding to three different cases involved in the measurements at the pilot laboratory: (a) the temperature difference between two TPW cells, which amounted to 26 μK (k = 2), (b) the temperature difference between a TPW cell and NRC national reference, which amounted to 35 μK (k = 2) and (c) the temperature difference between a comparison participant’s transfer cell and the comparison reference, composed of the average of two NRC national reference cells, which amounted to 19 μK (k = 2).

Improved Realization of Ensemble of Triple Point of Water Cells at CSIR-NPL

Improved Realization of Ensemble of Triple Point of Water Cells at CSIR-NPL

Precise temperature controlling algorithm for metrological adiabatic calorimeters based on proportional-integration (α) thermal energy

Thermal metrology laboratory at the National Institute of Standards (NIS-Egypt) has been working to realize the International Temperature Scale-1990 (Preston-Thomas in Metrologia 27:3–10, 1990). High-precision thermal control is required especially with low-temperature fixed points that were realized within adiabatic calorimeters. In this study, a new algorithm module has been developed to control precisely the accurate temperature based on equal partitioning the temperature domain to be equivalent to the sensitivity of controlling thermometer (0.00391 K−1). The algorithm technique is required to maintain and stabilize the temperature of an adiabatic evacuated copper can that is located inside a thermally isolated calorimeter; the modified fractional proportional-integration function and sensitivity partial temperature function (SPTF) for temperature control have been designed and developed. The improved discrete SPTF has showed a thermal stability better than 28 ± 1.8 mK at temperature extremely close to the triple point of water cell (Tcell = 273.16 K) with reliable response time within 18 ± 1 min of performance. The thermal parameters of the new adiabatic calorimeter have been calculated such as the heat capacity of the load and the thermal resistance between the regulated shield and the measuring sample. The estimated uncertainty related to the measurements has been improved to ± 0.28 mK.

On the long-term stability of the triple-point-of-water cells

Slow dissolution of the borosilicate container of triple-point-of-water (TPW) cell is widely recognized as the main cause of long-term drift in observed triple point temperature. We add to the available experimental data a comparison of two large batches of TPW cells (67 cells in total) of various ages (from 1 year to 64 years), manufacturers (NRC, VSL, Fluke, Isotech, etc), and materials (borosilicate glass and fused-silica) which was undertaken in 2018. After measuring the TPW temperatures realized by all 67 cells, 12 borosilicate cells were opened and their water was analyzed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) in order to correlate their impurity content with their respective age and their realized TPW temperature. No direct correlation was observed between the TPW cells age/impurity content and their measured triple-point temperature for neither borosilicate cells nor fused silica cells (Pearson’s correlation coefficient rxy is within the range −0.60 ≤ rxy≤ +0.40 for all the pairs considered). For fused-silica cells, the results indicate that after the isotopic variation in the water source is taken into account, the long-term drift due to the dissolution of glass envelope, if any, is negligibly small: (+0.4(±0.6) µK·yr−1 reported herein). Given that all the fused-silica cells realize the TPW temperature within 100 µK of NRC and VSL national reference cells and since the analyzed time period of 15 years is equal to the average lifespan of a TPW cell, we conclude that fused-silica TPW cells are superior to those made from borosilicate glass.

Final report on APMP.T-K7.1 key comparison of water triple point cells, bilateral NMIJ-VMI

APMP.T-K7.1, was held from July 2014 to May 2015 to compare the national realizations of the water triple point between NMIJ (Japan) and VMI (Vietnam). To reach the objective, VMI sent a transfer cell to NMIJ and stated a value for the temperature difference of the transfer cell, relative to the corresponding national standard, representing 273.16 K.This report presents the results of the TPW comparison, gives detailed information about the measurements made at the NMIJ and at the VMI, and aims to link the results of APMP.T-K7.1 to APMP.T-K7 and CCT-K7. The results of this key comparison are also represented in the form of degrees of equivalence for the purposes of the MRA.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Establishment of a New National Reference Ensemble of Water Triple Point Cells

The results of the Bilateral Comparison EURAMET.T-K3.5 (w/VSL, The Netherlands) with the goal to link Switzerland’s ITS-90 realization (Ar to Al) to the latest key comparisons gave strong indications for a discrepancy in the realization of the triple point of water. Due to the age of the cells of about twenty years, it was decided to replace the complete reference ensemble with new “state-of-the-art” cells. Three new water triple point cells from three different suppliers were purchased, as well as a new maintenance bath for an additional improvement of the realization. In several loops measurements were taken, each cell of both ensembles intercompared, and the deviations and characteristics determined. The measurements show a significant lower average value of the old ensemble of $$0.59 \pm 0.25\hbox { mK }(k=2)$$ in comparison with the new one. Likewise, the behavior of the old cells is very unstable with a drift downward during the realization of the triple point. Based on these results the impact of the new ensemble on the ITS-90 realization from Ar to Al was calculated and set in the context to performed calibrations and their related uncertainties in the past. This paper presents the instrumentation, cells, measurement procedure, results, uncertainties and impact of the new national reference ensemble of water triple point cells on the current ITS-90 realization in Switzerland.

New adiabatic calorimeter for realization the triple point of water in metallic-sealed cell at NIS-Egypt

The thermal metrology laboratory, at the National Institute for Standards (NIS-Egypt), has been working during the last three years on the development of metallic-sealed cells for the realization of the triple point of water (TPW), 273.16 K [H. Preston-Thomas, Metrologia 27, 3 (1990)]. A metallic-sealed cell has been already developed and characterized in the past [A. El Matarawy, M.G. Ahmed, Int. J. Metrol. Qual. Eng. 5, 401 (2014), M.G. Ahmed, A. El Matarawy, H.M. Abo Dorra, J. Phys. Sci. Appl. 1 (2015)]. The classical large triple point of water cell and metallic-sealed cell showed a discrepancy of 0.7 mK [A. El Matarawy, M.G. Ahmed, Int. J. Metrol. Qual. Eng. 5, 401 (2014)]. The main target of this work is to get the lowest possible uncertainty in calibrating Capsule Standard Platinum Resistance Thermometers (CSPRTs) under adiabatic conditions. The full system is composed of a metallic-sealed cell and an improved adiabatic calorimeter to increase as much as possible the thermal resistance between the cell and the inner adiabatic shield of the calorimeter. It gives also a reliable calculation of the heat capacity of the cell and the comparison copper block which accommodates several CSPRTs. With this new system the reproducibility of metallic-sealed cell was found to be 0.7 mK as described below. reproducibility of metallic-sealed cells is found to be less than 0.7 mK.

Final report on APMP.T-K7 key comparison of water triple point cells

APMP.T-K7, was held from February 2008 to September 2009 to compare the national realizations of the water triple point among eleven NMIs. To reach the objective, each participating laboratory sent a transfer cell to CMS and stated a value for the temperature difference of the transfer cell, relative to the corresponding national standard, representing 273.16 K.CMS (Taiwan) organized the comparison, with the support from co-pilot institutes MSL (New Zealand) and NMIJ (Japan). The other eight participating laboratories included NMIA, SCL, KIM-LIPI, KRISS, NMIM/SIRIM, NMC, NMISA, and NIMT.This report presents the results of the TPW comparison, gives detailed information about the measurements made at the CMS and at the participating laboratories, and aims to link the results of APMP.T-K7 to CCT-K7. The results of this key comparison are also represented in the form of degrees of equivalence for the purposes of the MRA.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Deep Ocean Temperature Measurement with an Uncertainty of 0.7 mK

AbstractThe uncertainty of deep ocean temperature (~1°C) measurement was evaluated. The time drifts of six deep ocean standards thermometers were examined based on laboratory calibrations as performed by the manufacturer in triple point of water (TPW) cells and gallium-melting-point (GaMP) cells. The time drifts ranged from −0.11 to 0.14 mK yr−1. Three of the six thermometers were evaluated at the National Metrology Institute of Japan in five TPW cells and a GaMP cell, and the temperature readings agreed with the realized temperature of the national standard cells of Japan within ±0.14 and ±0.41 mK for TPW and GaMP, respectively. The pressure sensitivities of the deep ocean standards thermometers were estimated by comparison with conductivity–temperature–depth (CTD) thermometers in the deep ocean, and no notable difference was detected. Pressure sensitivities of the two CTD thermometers were examined by laboratory tests, and the results suggest that the deep ocean standards thermometers have no pressure sensitivity, at least up to 65 MPa. The position and attitude motion of the CTD system can affect temperature and salinity data quality. The overall expanded uncertainty of the deep ocean temperature measurement (up to 65 MPa) by the CTD thermometer calibrated in reference to the deep ocean standards thermometer is estimated to be 0.7 mK.

Improvements in the realization of the triple point of water in metallic sealed cells at LNE-Cnam

Since 2008, LNE-Cnam has been working on the development of metallic sealed cells for the water triple point, temperature 273.16 K. The objective is to perform calibrations of capsule-type standard platinum resistance thermometers employing adiabatic calorimetry techniques, in order to get the lowest possible level of measurement uncertainty. After the realization of a preliminary prototype, the full system composed of new cells and an adiabatic calorimeter has been significantly improved. New cells have been manufactured, an ameliorated calorimeter has been built and improved procedures have been set up to clean, fill and seal the cells. Despite a remaining discrepancy of about 0.8 mK between metallic and traditional water triple point cells, the reproducibility of metallic cells has been improved to 0.1 mK. This paper describes the new devices developed and the results obtained. This work has been developed within the frame of the European metrology research program (EMRP) joint research project ‘SIB10 NOTED’. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.

Assessing Impurities in Triple-Point-of-Water Cells Using a Capacitance Conductivity Test

Chemical analysis of old triple-point-of-water (TPW) cells has shown that the dominant impurities in the water are the principal constituents of borosilicate glass, which suggests the long-term downward drift observed in the realized triple-point temperature of TPW cells is caused by gradual dissolution of the glass containers. Because some of the glass constituents contribute to the electrical conductivity of the water, measurement of the conductivity provides a possible means for monitoring the long-term drift of TPW cells. This paper investigates the utility of a conductivity measurement, based on the measurement of a capacitor using the TPW cell as a dielectric, as a non-destructive means for monitoring the long-term stability of cells. The measurement exploits the cylindrical geometry of the cell and uses a two-terminal-pair coaxial electrical definition of capacitance. The results include estimates of the sensitivity of the method and examples of the long-term behavior of TPW cells, some as old as 38 years and monitored for periods of up to 10 years. It is found that the conductivity measurements correlate well with the cell age, with the drift rates increasing with time, as expected from the chemical model of glass dissolution. Measurements of temperature differences between cells show the technique can detect changes as small as \(10~\upmu \hbox {K}\), and therefore the method is a useful means of monitoring TPW cells.

Effect of Impurities on Water Triple-Point Cells

Water triple-point cells are the basis for the definition of the kelvin and for the realization of the International Temperature Scale of 1990. The temperature differences between the cells are mainly caused by impurities arising in the cell water from the dissolution of the cell envelope (borosilicate glass or quartz). In order to investigate the effects of such impurities on the realized triple-point temperature, water triple-point cells doped with known amounts of Si and Na impurities ( $$0.1\,{\upmu }\hbox {mol}{\cdot }\hbox {mol}^{{-1}}$$ to $$1\,{\upmu }\hbox {mol}{\cdot }\hbox {mol}^{{-1}}$$ of Si and $$0.2\,{\upmu }\hbox {mol}{\cdot }\hbox {mol}^{{-1}}$$ to $$2\,{\upmu }\hbox {mol}{\cdot }\hbox {mol}^{{-1}}$$ of Na) were manufactured at VSL by adding gravimetric mixtures of a Si standard reference material and ultra high-purity water to the cell high-purity water. Water samples were taken from the manufactured cells, partitioned into three samples, and distributed to different laboratories for isotope and impurity analysis (inductively coupled plasma mass spectrometry, ICPMS). The results of two independent ICPMS analyses were compared with impurity calculations based on the gravimetric data of the prepared mixtures and manufactured cells. One undoped cell manufactured by UME and one undoped cell manufactured by VSL were intercompared at both VSL and SMD to demonstrate the equivalence of the manufacturing processes of UME and VSL. The triple-point temperatures realized by the doped cells and the undoped cell manufactured by VSL were measured at SMD. The results showed that, in doped cells, the equilibration time after the last freezing is directly dependent on the impurity concentration, and the temperature depression of doped triple-point-of-water cells is significantly greater than the values predicted by Raoult’s law for an ideal dilute solution.

An Alternative Method for Manufacturing Water Triple-Point Cells

Water triple-point (WTP) cells are the most important standards in laboratories that calibrate standard platinum resistance thermometers (SPRT). Over the years, different methods for manufacturing WTP cells have been proposed; some quite simple, others more complex. This paper describes a straightforward method for manufacturing WTP cells. The method is based on the fact that the pressure present when water is boiling is its vapor pressure, and because of that the amount of residual dissolved gases, if any, is very small. This makes the use of vacuum pumps unnecessary. The bulb of the WTP cell is filled with pure water produced by multiple distillations or by deionizer systems. The water is then boiled inside the bulb by a furnace built specifically for this purpose. After boiling the water for at least 30 min, the furnace is switched off, and a valve connected to the filling port of the cell is closed, in order to ensure that only water vapor and liquid water are present inside the WTP cell. The cell is then removed from the furnace and sealed when its temperature decreases. The paper also describes the procedure used to evaluate the WTP cells manufactured by this method, through comparisons against other reference standards, manufactured by more traditional approaches. The results show that the temperatures of the WTP cells manufactured by this new method have similar values to the ones obtained in WTP cells manufactured by traditional methods.

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.

Traceability of temperature measurements in Estonia

This paper presents an overview of the establishment of the national measurement standard for temperature at METROSERT - the national metrology institute in Estonia. The temperature scale and traceability arrangements are realized in the temperature range from - 40 °C to + 300 °C by means of a group of calibrated standard platinum resistance thermometers and water triple point cells. The linkage of the realized water triple point temperature to the international key comparison value with the expanded uncertainty of 187 µK (coverage factor k = 2) is demonstrated. The established laboratory is capable of providing calibration services to customers by comparison calibration with the expanded uncertainty (k = 2) values of 5 mK in the range from - 40 °C to + 200 °C and 12 mK in the range from + 200 °C to + 300 °C.

Final report on EURAMET.T-K7.1: Bilateral key comparison of water triple point cells

This is the final report of key comparison EURAMET.T-K7.1, a bilateral comparison of water triple point cells between the Czech Metrology Institute, CMI, and the Slovensky Metrologicky Ustav, SMU, of Slovakia. The comparison was requested by CMI, and the measurement protocol was compatible with the one used for key comparison EUROMET.T-K7. The results show a satisfactory degree of equivalence between SMU and CMI, and allow linkage to the parent key comparison EUROMET.T-K7. As a consequence, CMI is able to support CMCs at the temperature of the triple point of water and submit them for publication in the KCDB.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Improvements in the measurement of the immersion profile of water triple points using bushes

The triple point of water is the most important fixed point, both used as the defining fixed point for the definition of the Kelvin and also the pivotal fixed point for the realization of the International Temperature Scale of 1990 (ITS-90). As such, obtaining the best performance from the water triple point is vital. This comparative study focuses on the benefits of using long bushes (that cover most of the length of the thermowell) for improving the repeatability of the immersion profile for water triple point cells. It is shown that the use of long bushes helps by improving a) the thermal contact between the thermometer and the ice sheath and b) the repeatability of locating the thermometer inside the thermowell. To investigate the reproducability of the immersion profile for triple point of water cells, two different types of Standard Platinum Resistance Thermometers (SPRTs) have been used. The SPRTs have different designs, different length of sensing element and different self heating effects. These experiments were carried out using the same water triple point cell to identify thermometer specific effects. To measure the immersion profile, the following factors have to be taken into account: a) the effect of hydrostatic pressure, since the measurements are made at different depths below the water surface; b) the effect of heat flux along the thermometer stem; c) the need of long thermal stabilization at every immersion depth. The experimental results reported here show that repeatability in the determination of immersion profiles was significantly improved (by a factor of at least two) through the use of long bushes and when measured with a SPRT with a low self-heating effect.