Triple Point Of Water Research Articles

ITS-90 non-uniqueness and evaluation of characteristics of new 1000 Ω type platinum resistance thermometers for low-temperature measurement

For use in a low-temperature region below the triple point of water (TPW), the National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST) developed a precise comparison system of capsule-type standard platinum resistance thermometers (CSPRTs) for dissemination of the International Temperature Scale of 1990 (ITS-90). This study compared eight CSPRTs with a reference CSPRT using the comparison system to study non-uniqueness at low temperature. We also evaluated characteristics of a new type of low-temperature PRT with about 1000 Ω of resistance at TPW (PT-1000s), which was recently developed by Netsushin Co, Ltd. to obtain better temperature sensitivity of resistance at a low temperature. The PT-1000 sensor is made from a high-grade platinum wire, similarly to standard PRTs of the ITS-90. We calibrated four PT-1000s based on the ITS-90 and evaluated their characteristics by comparison with a reference CSPRT. Results indicate that the character of the temperature scale of PT-1000s is very close to that of CSPRTs down to 14 K.

Stability of the Liquid Water Phase on Mars: A Thermodynamic Analysis Considering Martian Atmospheric Conditions and Perchlorate Brine Solutions.

The stability of the liquid water phase on Mars has been examined on the basis of fundamental thermodynamic principles. The analysis considers the atmospheric pressure and temperature conditions prevalent on Mars. Because of the very low atmospheric pressure on Mars, water cannot exist in the liquid form. However, salt dissolution can reduce the freezing point and elevate the boiling point of aqueous solutions. This is interesting in the light of the discovery of perchlorate, sulphate, sodium, potassium, and calcium ions over the Martian surface. The effect of different perchlorate salts on the freezing and boiling points of water while considering their saturation solubility under varying ionic conditions is key to this analysis. It is shown that under an average atmospheric pressure of 600 Pa, the saturated solution of sodium perchlorate (NaClO4) is stable in the liquid phase in the temperature range between 240 and 275 K. The triple point of water under this condition is shifted to 269 K with a saturation solubility of 14.4 mass % of the salt. However, a saturated solution of magnesium perchlorate (Mg(ClO4)2) renders this temperature range wider from 198 to 296 K, with the triple point being located at 269 K (salt saturation at 13.5 mass % salt). In case the water is contaminated with a mixture of these salts, an increased stability is predicted for liquid water down to 180 K and up to at least 298 K. This is caused by the increased ionic strength that enhances the freezing point depression and boiling point elevation of the solution. Thus, in the extreme and uneventful conditions of saturation by mixtures of salts, liquid water can be stable on Mars between 180 K and at least up to 298 K. Below this temperature, water exists as a glacier and above, as steam only.

Investigation of the thermal stability of PtO2 and dislocations in Pt wire

Abstract The thermal stability of PtO2 and dislocation density within Pt wire were investigated using differential scanning calorimetry (DSC), Thermogravimetry (TG), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) to understand and evaluate the stability of standard platinum resistance thermometer (SPRT), which is the interpolation instrument in the International Temperature Scale of 1990 (ITS-90). Through analyzing the thermal stability of PtO2, the results showed that PtO2 decomposition was closely related to the thermal process. PtO2 did not decompose below 500 °C in air but began to decompose into PtO and Pt above 550 °C. The decomposition rate of PtO2 was shown to be the fastest at 620 °C, but the decomposition was not necessarily complete at this temperature. The decomposition process of PtO and PtO2 further occurred from 800 °C to 850 °C. Through analyzing the thermal stability analysis of Pt wire dislocation, the results showed that the total dislocation density of platinum wire decreased exponentially with an increase in annealing time. After 100 h annealing, the dislocation density decreased from 1012 cm−2 to 1011 cm−2, and after 300 h annealing, the dislocation density tended to be stable. Twelve SPRTs recently made in NIM were annealed at 660 °C, the resistance changes of SPRTs at the triple point of water were similar to the trend of dislocation density with annealing time. Therefore, to reduce long-term downward drifts, it is recommended to anneal more than 300 h for new SPRTs before calibration.

Thermodynamic Temperature Measurements from the Triple Point of Water up to the Melting Point of Gallium

A new acoustic gas thermometry (AGT) system, which introduces a 1-L quasi-spherical resonator (QSR) made of oxygen-free copper, was built at the National Metrology Institute of Japan (NMIJ/AIST). The inner surface of the new QSR was machined using a diamond-turn tool. Improvement in the pressure measurement was introduced to allow direct measurement of the gas pressure in the resonator. The new AGT system was evaluated based on the measurement of the speed of sound in argon at the triple point of water and the melting point of gallium under the pressure range from 700 kPa down to 50 kPa. Based on these speed of sound measurements, the thermodynamic temperatures at the melting point of gallium were determined. The speed of sound measurements at isotherms of 283.15 K and 293.15 K were also conducted, and the related thermodynamic temperatures were determined. Based on the measured thermodynamic temperature T, the values of difference between T and the temperature T90 based on the International Temperature Scale of 1990 (ITS-90), (T − T90), along with the associated uncertainties, were calculated. The (T − T90) obtained in the present work were 1.3 ± 0.7 mK, 2.7 ± 0.8 mK, and 4.1 ± 0.8 mK for T90 of 283.15 K, 293.15 K, and 302.9146 K, respectively. These values were found to be in agreement within the estimated uncertainty with the currently reported values that exist in temperature range overlapping with the present work.

Evaluation of High-Temperature Platinum Resistance Thermometers Based on ITS-90

High-temperature standard platinum resistance thermometers (HTSPRTs) are used to establish the International Temperature Scale of 1990 (ITS-90) for temperatures up to 960 °C. Currently available thermometers, which may differ in the design of the platinum winding of the sensor, the shape and finish of the sensor frame, the frame material, the protective sheaths, and sealing materials, need some treatments to exhibit the stabilities expected of them and some of the causes of the instability are not well understood. This paper demonstrates a novel model of commercial HTSPRT that reportedly employs a novel sensor winding construction designed to eliminate instability arising from strain on the sensor winding due to differential thermal expansion between the sensor and the sensor frame. The stability of eight different HTSPRTs, including the novel model, are compared at the triple point of water (TPW), the melting point of gallium, and the freezing points of tin, zinc, aluminum and silver. Heat treatments included annealing at 500 °C, a preheating temperature for use at the freezing points of aluminum and silver, and at 800 °C, which was selected for checking the stability of the HTSPRTs in the middle of the temperature range between the freezing points of aluminum and silver. The consistency of the resistance values at the different fixed points was also confirmed by calculating the S parameter. We found three HTSPRTs stable during the described thermal conditions within ± 0.5 mK at the TPW. The novel model of commercial HTSPRT was the best one with a stability in the resistance at the TPW of within ± 0.3 mK over the entire temperature range. These indicate that the stable three HTSPRTs are promising instruments to provide accurate temperature scale at temperatures from the freezing point of aluminum up to the freezing point of silver based on the ITS-90.

Realization of the ITS-90 from 273.16 K to 692.677 K

The bilateral comparison of the ITS-90 realizations at the National Metrological Institutes of Germany (PTB) and the Russian Federation (VNIIM) in the temperature range from 273,16 K to 692,677 K was initiated by the Technical Committee on "Thermometry and thermal physics" TC1.10 of COOMET.The purpose of the comparison was to evaluate the differences between the realizations of the national standards in the most essential temperature range with the highest requirements to the measurement uncertainty. This temperature range includes five ITS-90 fixed points: the triple point of water, the melting point of gallium, the freezing points of indium, tin and zinc.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).

Temperaturskalan och Boltzmanns konstant

Temperature scale and the Boltzmann constant: The newest system of units is based on a compatible set of natural constants with fixed values. An example is the Boltzmann constant k which defines the thermal energy content kT. To express the base unit T, the absolute temperature in kelvin, an international agreement for the temperature scale is needed. The scale is defined using fixed points, which are temperatures of various phase transitions. Especially important has been the triple point of water at 273.1600 K. These fixed point temperatures determine the international temperature scale ITS within the Si system. Temperature measurement itself is based on physical laws and on the properties of appropriate thermometric materials selected to determine the temperature scale. For determining the Boltzmann constant, new precision techniques have been developed during the last two decades. Examples are different types of gas thermometry, which ultimately are based on the ideal gas law, and thermal noise of electric charge carriers in conductors. With these means it has become possible to fix the value of the Boltzmann constant with a relative uncertainty of < 1 ppm. As of 2019, the value of k has been agreed to be fixed at 1.380649x10^(-23) J/K. This agreement replaces the earlier definition of a Kelvin degree.

Role of zero point energy in promoting ice formation in a spherical drop of water

We demonstrate that the Lifshitz interaction energy (excluding the self-energies of the inner and outer spherical regions) for three concentric spherical dielectric media can be evaluated easily using the immense computation power in recent processors relative to those of a few decades ago. As a prototype, we compute the Lifshitz interaction energy for a spherical shell of water immersed in water vapor of infinite extent while enclosing a spherical ball of ice inside the shell, such that two concentric spherical interfaces are formed: one between solid ice and liquid water and the other between liquid water and gaseous vapor. We evaluate the Lifshitz interaction energy for the above configuration at the triple point of water when the solid, liquid, and gaseous states of water coexist, and, thus, extend the analysis of Elbaum and Schick in Phys. Rev. Lett. 66 (1991) 1713 to spherical configurations. We find that, when the Lifshitz energy contributes dominantly to the total energy of this system, which is often the case when electrostatic interactions are absent, a drop of water surrounded by vapor of infinite extent is not stable at the triple point. This instability, that is a manifestation of the quantum fluctuations in the medium, will promote formation of ice in water, which will then grow in size indefinitely. This is a consequence of the finding here that the Lifshitz energy is minimized for large (micrometer size) radius of the ice ball and small (nanometer size) thickness of the water shell surrounding the ice. These results might be relevant to the formation of hail in thunderclouds. These results are tentative in that the self-energies are omitted; surface tension and nucleation energy are not considered.

EURAMET-T.K9.1 bilateral comparison of ITS-90 SPRT calibration from the Hg TP to Zn FP

Justervesenet (JV, Norway) and Metrosert (Estonia) agreed in 2016 to conduct a bilateral comparison of SPRT calibrations for the fixed points from the triple point of Hg to the freezing point of Zn, with the exception of the freezing point of In which Metrosert could not realise. The aim of the comparison was to link Metrosert to the CCT-K9 via the EURAMET-T.K9. JV was the linking laboratory to the EURAMET-T.K9 and the pilot. An SPRT was first calibrated at Metrosert, shipped to JV and calibrated there, and finally returned to Metrosert for a second calibration. The measurements were carried out and completed in 2017.The results show that the laboratories involved are in agreement. At the triple point of Hg and the melting point of Ga the results are consistent and agree at all three reported measurements. At the freezing points of Sn and Zn Metrosert observes some change in W-values, although the difference is smaller than the reported uncertainty. The difference may suggest some drift either in the circulating probe or in the reference equipment at Metrosert, and this discrepancy increased the uncertainty in the degree of equivalence somewhat.The resistance of the probe was measured at the triple point of water after every fixed point, and prior to and after annealing upon reception at the laboratories. In general the resistance values are stable, but may suggest some drift between the first measurements at Metrosert and the measurements at JV.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).

Thermal picks for anchoring on icy moons

Europa, Enceladus, and other icy moons are exciting science targets, but our capabilities to adequately explore these planetary bodies needs to be developed. Gripping the surface ice may aid the stability and mobility of surface landers and mobile explorers that are sent to the surface of an icy moon. This paper presents an approach to anchoring into the surface of an icy moon using a heated pick.The proposed thermodynamic approach contrasts with the traditional mechanical approach to inserting terrestrial ice anchors. This thermodynamic approach maintains the ice structure to provide a reliable hold. The low temperatures and lack of a significant atmosphere on most of the icy moons cause surface conditions to stay below the triple point of water, the primary constituent of the surface ice for both Europa and Enceladus. Under these conditions the surface water ice will sublimate when sufficiently heated. The thermal pick concept presented in this paper is used to study the nature of the sublimation that results from forced insertion of an object into ice, which could then be used as an anchor for stability and mobility.While the surfaces of the icy moons are composed primarily of water ice at cryogenic and vacuum conditions, the nature of a sublimation process can be more readily examined with frozen CO2, which sublimates under atmospheric conditions. This paper explores the physical phenomena and thermodynamic design considerations of a heated device that uses a sublimation based insertion into frozen CO2 under atmospheric conditions. This approach was found to allow for proper insertion of thermal picks with energetic efficiencies of up to 90%.

Speed of sound measurements in liquid methane ([formula omitted]) at cryogenic temperatures between (130 and 162) K and at pressures up to 10 MPa

This paper reports speed of sound experimental measurements in liquid methane (CH4) along five isotherms, in the temperature range of (130 and 162) K, and for pressures up to 10 MPa. A dedicated experimental apparatus, custom-designed for accurate speed of sound measurement at cryogenic temperatures and high pressures, has been developed and the double pulse-echo technique has been adopted. In order to characterize this new apparatus and its performance, experimental results have been compared with speed of sound values of liquid methane available in literature. A further comparison has been made between the experimental measurements and the speed of sound values obtained using the reference equation of state of methane of Setzmann and Wagner, as well as the GERG-2008 model. The ultrasonic path-length has been calibrated using pure water as a reference fluid, with a relative uncertainty of 0.026%. The temperature was measured with two platinum resistance thermometers with an absolute uncertainty of 0.02 K. Thermometers have been calibrated using the ITS-90 temperature scale between the triple point of argon and the triple point of water. Finally, the relative expanded uncertainty (k = 2) associated to the obtained results is of 0.4%, mainly influenced by the repeatability of the measurements.

Equations for Engineering Calculations of the Thermodynamic Properties of High-Temperature Dissociated Steam

A system of equations is developed to calculate the properties of dissociated steam in the temperature and pressure ranges of 1250–3400 K and 0.01–10.00 MPa. These equations are based on detailed tables for dissociated steam compiled for a mixture of atoms of hydrogen and oxygen, hydroxyl OH, molecules of hydrogen and oxygen, and steam at a reference temperature of 0 K. Since the expansion of dissociated steam in a thermal engine results in its transformation into its common form, the equations for the parameters of dissociated or nondissociated steam uses the same reference temperature, i.e., the water triple point of 273.16 K. A system of equations for the calculation of dissociated-steam properties is derived with the generalized thermodynamic equation, which takes into account the change in the chemical potential and the composition of the mixture during steam dissociation, the Gibbs energy equation, differential thermodynamic equations, and equations for calculation the properties of nondissociated steam. To minimize the deviation of the steam properties calculated by the proposed equations from the table values, the considered temperature and pressure ranges have been divided into three regions. The deviation of the steam properties calculated by the proposed equations from the table values does not exceed 0.05–0.09%. The developed equations can be used in calculations of the processes of cooling of burners and combustion chambers during the combustion of hydrogen–oxygen mixtures, as well as cycles of heat engines that use high-temperature steam as a working fluid at temperatures over 1250 K.

Highly-accurate density-virial-coefficient values for helium, neon, and argon at 0.01 ○C determined by dielectric-constant gas thermometry.

The dielectric-constant gas thermometer of Physikalisch-Technische Bundesanstalt (PTB) developed for measuring the Boltzmann constant with a relative uncertainty of 1.9 parts per million was used for determining the virial coefficients of the three noble gases, helium, neon, and argon, at the triple point of water (0.01 ○C). For this purpose, isotherms were measured up to a maximum pressure of 7 MPa. The evaluation of the highly accurate data by fitting is required to derive an extended working equation for the dependence of the gas pressure on the dielectric constant. The following values have been obtained for the second B and third C virial coefficients, with the standard uncertainties given in parentheses as a multiple of the last digit, considering literature data for the dielectric virial coefficients: helium: BDCGT He0.01 ○C=11.925715 cm3/mol, CDCGT He0.01 ○C=113.4958 cm6/mol2; neon: BDCGT Ne0.01 ○C=10.994528 cm3/mol, CDCGT Ne0.01 ○C=215.815 cm6/mol2; argon: BDCGT Ar0.01 ○C=-21.233144 cm3/mol, CDCGT Ar0.01 ○C=1143.339 cm6/mol2. These values are compared with the results of the latest ab initio calculations of the second and third virial coefficients.

Cesium atomic Doppler broadening thermometry for room temperature measurement

Atomic Doppler broadening thermometry (DBT) is potentially an accurate and practical approach for thermodynamic temperature measurement. However, previous reported atomic DBT had a long acquisition time and had only been proved at the triple point of water, 0°C, for the purpose of determination of the Boltzmann constant. This research implemented the cesium atomic DBT for fast room temperature measurement. The Cs133 D1 (6S1/2 → 6p1/2 transition) line was measured by direct laser absorption spectroscopy, and the quantity of thermal-induced linewidth broadening was precisely retrieved by the Voigt profile fitting algorithm. The preliminary results showed the proposed approach had a 4 min single-scan acquisition time and 0.2% reproducibility. It is expected that the atomic DBT could be used as an accurate, chip-scale, and calibration-free temperature sensor and standard.

Comparison of xenon triple point realizations

It is widely recognized that the Mercury triple point (MTP) being situated very close to the Water triple point (WTP) constitutes a weakness in the International Temperature Scale of 1990 (ITS-90), in addition to safety concerns related to the use and transportation of Mercury. As such, a substitution for a safer, high-quality fixed point about half way between the Argon and Water triple points would be highly desirable. Now, a direct comparison is described of a Xenon cell filled in 2005 by the National Research Council Canada (NRC) and a more recently produced cell of the Istituto Nazionale di Ricerca Metrologica (INRIM). The present paper discusses the INRiM 2017 measurements on both the INRiM and NRC cells, with a follow-up measurement at NRC, and presents the difference between the two cells, (0.17 ± 0.08) mK with the uncertainties of each cell’s realization of the Xenon triple point (XeTP), 0.11 mK for the INRiM cell and 0.07 mK for the NRC cell (k = 1). In addition, the effect of substituting Mercury with Xenon on Type 1 non-uniqueness (‘SRI’, subrange inconsistency), Type 3 non-uniqueness (‘NU3’, cSPRT variability) and propagation of fixed point realization uncertainty is shown and discussed.

Comparison of the realization of water triple point metallic cell through its preparation techniques in new modified adiabatic calorimeter at NIS-Egypt

The triple point of water (TPW, temperature 273,16 K) plays a vital and critical role in thermometry, because of its triple functions. The first one, it defines the temperature unit, the Kelvin, it is the reference point in Standard Platinum Resistance Thermometer (SPRT) calibrations, according to the International Temperature Scale of 1990 (ITS-90) [1]. On the other side, TPW metallic-sealed cell is the link to determine Boltzmann constant through the acoustic resonance techniques. TPW is the connection point between the current definition of the Kelvin and the future one, based on the Boltzmann constant [2]. The uncertainty related to the realization of TPW will propagate in all fixed point defined by ITS-90 text. The thermal metrology laboratory, at the National Institute for Standards (NIS-Egypt), has been working during the last 5 years with the cooperation with LNE-France on the development of metallic-sealed cells for the realization of the TPW [1, 2, 3, 4]. Two techniques to solidify the water sample inside the cell were tested, the usual one; quenching (fast freezing) and a new modified smoothing (slow freezing starts at 90% of melted ice). The calculated value of impurities concentration was carried out; it is about of 1.29 × 10−6 mol. mole−1 which causes a deviation of about 142 μK. The uncertainty related to the realization of TPW has been improved up to ± 30 mK.

Development of absolute acoustic gas thermometer for the state primary standard of the temperature unit – kelvin in the range 0.3-273.16 K in VNIIFTRI and the total standard uncertainty of the thermodynamic temperature measurements near the triple point of water

An absolute primary acoustic gas thermometer has been developed and successfully tested in VNIIFTRI. The acoustic gas thermometer is planned to be included in the Russian state primary standard of the temperature unit – kelvin in the range 0.3-273.16 K. The uncertainty of the thermodynamic temperature measurements with the acoustic gas thermometer near the triple point of water was experimentally researched.

Melting probe experiments under Mars surface conditions – the influence of dust layers, CO2-ice and porosity

This paper reports about recent melting probe experiments under a pressure that is within the pressure regime at the surface of Mars. As compared to the results given in Kömle et al. (2018), the experiments were extended in several aspects: (i) A deeper ice sample was used in order to study the performance of the probe in the subsurface, (ii) dust layers were embedded inside the samples in order to study their influence on probe penetration, (iii) a surface cover of granular CO2-ice was added, in order to study the performance of the probe in the presence of dry ice, and (iv) the performance of the melting probe in a highly porous ice layer (fresh bonded snow) was studied. In addition, the case of several heating cycles, interrupted by cooling periods, was considered. The experiments demonstrated that the melting probe concept remains successful also in the presence of embedded sand and dust layers, as long as such non-volatile layers are thin, say in the order of centimetres. Under Mars pressure there is always liquid water present in the melt hole, except for the fresh bonded snow case, where the melt water is absorbed by the surrounding snow. However, because the Mars surface pressure is typically just slightly above the water triple point pressure, this water is permanently boiling and there are strong convective motions which whirl up dust particles and remove them at least partially from the hot nose region. The presence of a porous CO2-ice cover on the surface does not seriously hamper melting probe penetration, because CO2-ice is much more volatile than water ice and the probe passes such a layer very fast when heated with the same power. In fresh bonded snow, which has very high porosity, the probe penetrates correspondingly faster than in compact ice. Finally, in the last experiment, it was demonstrated explicitly that the melting probe concept works also, when heating is applied in several cycles, interrupted by periods of no active heating.

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.

Accurate Determination of the Values of Fundamental Physical Constants: The Basis of the New “Quantum” SI Units

The metric system appeared as the system of units designed for macroscopic (laboratory scale) measurements. The progress in accurate determination of the values of quantum constants (such as the Planck constant) in SI units shows that the capabilities in high-precision measurement of microscopic and macroscopic quantities in terms of the same units have increased substantially recently. At the same time, relative microscopic measurements (for example, the comparison of atomic transition frequencies or atomic masses) are often much more accurate than relative measurements of macroscopic quantities. This is the basis for the strategy to define units in microscopic phenomena and then use them on the laboratory scale, which plays a crucial role in practical methodological applications determined by everyday life and technologies. The international CODATA task group on fundamental constants regularly performs an overall analysis of the precision world data (the so-called Adjustment of the Fundamental Constants) and publishes their recommended values. The most recent evaluation was based on the data published by the end of 2014; here, we review the corresponding data and results. The accuracy in determination of the Boltzmann constant has increased, the consistency of the data on determination of the Planck constant has improved; it is these two dimensional constants that will be used in near future as the basis for the new definition of the kelvin and kilogram, respectively. The contradictions in determination of the Rydberg constant and the proton charge radius remain. The accuracy of determination of the fine structure constant and relative atomic weight of the electron has improved. Overall, we give a detailed review of the state of the art in precision determination of the values of fundamental constants. The mathematical procedure of the Adjustment, the new data and results are considered in detail. The limitations due to macroscopic properties of material standards (such as the International prototype of the kilogram) and the isotopic composition of substances involved in precision studies in general (as standard measures for the triple point of water) and, in particular, in the determination of the fundamental constants are discussed. The perspectives of the introduction of the new quantum units, which will be free from the mentioned problems, are considered. Many physicists feel no sympathy for the International system of units (SI), believing that it does not properly reflect the character of physical laws. In fact, there are three parallel systems, namely the systems of quantities, system of their units and the related standards. The definition of the units, in particular, the SI units, above all, reflects our ability to perform precision measurements of physical values under certain conditions, in particular, to create appropriate standards. This requirement is not related to the beauty of fundamental laws of nature. More accurate determination of the fundamental constants is one of the areas where we accumulate such experience.