Thermodynamic Temperature Measurements Research Articles

Quantitative analysis of the impact of room temperature stability on cryostat performance

The constant temperature in laboratories is crucial for precise low-temperature measurements. Currently, there are no reports on the specific temperature needs for such experiments or quantitative analyses of how room temperature fluctuations affect cryostat control. This paper proposes a method to quantitatively analyze these fluctuations and their impact on cryostat temperature control. Taking the cryostat using for 2 K-5 K thermodynamic temperature measurement as the research object, and conducts model simulation and experimental validation. The research results indicate the primary influence on the sphere’s temperature is the time-dependent fluctuation of the room temperature. As temperature fluctuations propagate from the cryostat’s outer casing to the sphere, heat conduction is the dominant factor. The temperature fluctuations inside the system caused by environmental temperature fluctuations can be quantitatively expressed by a simple linear formula, with the coefficient being the fluctuation attenuation rate, which is 6.590 × 10-4 in this system. The deviation between experimental results and simulation results is within 5 %. To keep the sphere’s ambient temperature influence below 0.077mK, or 20 % of cryocooler-induced fluctuations, the room temperature must be controlled within 0.12 °C. In addition, the fluctuation period of room temperature is controlled below 1 h, the 0th flange is thickened, the rod is lengthened, and the material of the rod is changed to G10 above 4.2 K and stainless steel below 4.2 K can also effectively attenuate the influence on system temperature control.

Simulation analysis for controlling temperature stability of a radiant-board system served for thermodynamic temperature measurement laboratory

Simulation analysis for controlling temperature stability of a radiant-board system served for thermodynamic temperature measurement laboratory

Thermodynamic Temperature Measurements from the Melting Point of Gallium Down to the Triple Point of Mercury

Thermodynamic Temperature Measurements from the Melting Point of Gallium Down to the Triple Point of Mercury

Thermodynamic temperature measurements of Al–Cu, Al, Ag, Cu and Co–C fixed points by radiometry hybrid method

The radiometry hybrid method, by introducing a lens to the irradiance method with a 900 nm filter radiometer, was adopted to measure the thermodynamic temperature of the aluminum-copper (Al–Cu) eutectic point, aluminum (Al) freezing point, silver (Ag) freezing point, copper (Cu) freezing point and cobalt carbon (Co–C) eutectic point at the National Institute of Metrology, China. By scanning the uniformity of fixed-point blackbodies, the effective diameters were accurately estimated according to the size of the source effect (SSE). The lens transmittance measurement with the closest diameter aperture was adjusted to reduce the uncertainty of SSE. The discrepancy between the thermodynamic temperature and ITS-90 values (T-T 90) of Al–Cu, Al, Ag, Cu and Co–C fixed point blackbodies were concluded as 0.022 °C, 0.014 °C, 0.097 °C, 0.137 °C and 0.317 °C, respectively. The standard uncertainty of the fixed point thermodynamic temperature was estimated to be (0.1 to 0.3) °C (k = 2).

2022 Update for the Differences Between Thermodynamic Temperature and ITS-90 Below 335 K

In 2011, a working group of the Consultative Committee for Thermometry published their best estimates of the differences between the thermodynamic temperature T and its approximation (T90), the temperature according to the International Temperature Scale of 1990, ITS-90. These consensus estimates, in combination with measurements made in accordance with ITS-90, are an important alternative to primary thermometry for those requiring accurate measurements of thermodynamic temperature. Since 2011, there has been a change in the definition of the kelvin and significant improvements in primary thermometry. This paper updates the (T − T90) estimates by combining and analyzing the data used for the 2011 estimates and data from more recent primary thermometry. The results of the analysis are presented as a 12th-order polynomial representing the updated consensus values for the differences and a sixth-order polynomial for their uncertainty estimates.

Definition of uncertainty of temperature measured via thermocouple in various sources of errors

One of the most significant issues for researchers of thermodynamic temperature measurements is the evaluation of realiability of measurement results. Thus, while thermodynamic measuring of the temperature with thermocouples, it is essential to specify uncertainty before making decision on the reliability of measuring data during temperature measurements. The research surveys justified that uncertainty of the temperature specified via thermocouple is affected by the types of errors, such as the limits of division of the structure of data collection, the error of the compensation of reference junction, the error of temperature measurement based on the specification of tension and data variability as well. During the studies different experiments using HIOKI (LR8402-20) data registrator for the definition of data changes and the errors of compensation of reference node has been carried out, as well as the procedure of specification of temperature uncertainty including compensated node uncertainty is suggested.

Realisation of the ITS-90 and thermodynamic temperature measurements above 960 °C using a monochromator-based radiance comparator

At LNE-Cnam, the international temperature scale of 1990 (ITS-90) and thermodynamic temperature measurements above the silver point, are carried out with a radiance comparator. This instrument is, more generally, devoted to any radiance comparison in temperature range from the ambient to 3000 °C. The instrument developed in the early 1990s at LNE-Cnam has the advantage of being completely adjustable. Compared to compact radiation thermometers based on lenses and a narrow-band interference filter, the radiance comparator is only made of gold coated mirrors and a Czerny–Turner monochromator to select the spectral bandwidth. The instrument offers the possibility to tune the geometric extent and the slit scattering function. In return, the radiance comparator is a complex instrument that requires a complete and a regular characterisation at the highest level of accuracy. In the first part, this paper describes the instrument and its operating principle. In a second part, a complete study of the wavelength calibration, the slit scattering function, size of source effect, out-of-band transmittance, linearity and other main sources of uncertainty are presented and discussed. Their associated uncertainties are estimated separately and are grouped together to give an example of propagation of uncertainties when realising the ITS-90.

Primary thermometry at 4 K, 14 K, and 25 K applying dielectric-constant gas thermometry

This short note is a supplement to the paper ‘Primary thermometry from 2.5 K to 140 K applying dielectric-constant gas thermometry’ (2017 Metrologia 54 141–7). It deals with thermodynamic temperature measurements at the boiling point of the heavy isotope of helium (4He, 4 K) and the triple points of hydrogen (14 K) and neon (25 K). This is of special interest because recent data published in this temperature range have an unexpectedly large spread. The results presented in this short note show that the International Temperature Scale of 1990, ITS-90, is thermodynamically correct at 4 K and 14 K, but too high by about half a millikelvin at 25 K. Furthermore, care is given to two aspects of dielectric-constant gas thermometry in the low-temperature range. First, dielectric-constant gas thermometry can be applied for practical primary thermometry. The measurement of only one isotherm in one day yields a temperature value with an uncertainty order of a few tenths of a millikelvin. Second, the use of recent ab initio values for the virial coefficients of helium as a measuring gas can reduce the efforts significantly. Even one data pair of pressure and dielectric constant can yield a thermodynamic temperature value of uncertainty less than a factor of two larger compared to the uncertainty of the usually used fit evaluation. For 4 K and 25 K, the achieved final uncertainty for T is still larger than the realization uncertainty of T 90. Thereby in the case of 14 K, both uncertainties are comparable.

Measurement of thermodynamic temperature between 5 K and 24.5 K with single-pressure refractive-index gas thermometry

We describe measurements of thermodynamic temperature in the range 5 K to 24.5561 K (the triple point of neon) using single-pressure refractive-index gas thermometry (SPRIGT) with 4He. In the wake of the May 2019 re-definition of the kelvin and its associated mise en pratique, the main purpose of the work is to provide values of T–T 90, the discrepancy between thermodynamic temperature and that of the International Temperature Scale of 1990 (ITS-90). The link to ITS-90 is made via calibrated rhodium-iron resistance thermometers. Innovations required to reach the level of accuracy required for meaningful measurements (uncertainty in T–T 90 less than the expected deviation) include the suppression of temperature oscillations in a cryogen-free cryostat, a pressure stabilization scheme based on a non-rotating piston balance, modelling of the hydrostatic head correction and refinements of the measurement of microwave resonances in a quasi-spherical copper resonator. The accuracy of measurements varies from 0.05 mK to 0.17 mK and is competitive with that of all previous ones in this temperature range using other techniques. The improvement stems partly from the new techniques used for the new definition of the kelvin as well as ab initio calculations of the thermophysical properties ofgaseous 4He. In addition to confirming the validity of SPRIGT as an accurate, easier-to-implement alternative to other low-temperature primary thermometry techniques (e.g. acoustic gas thermometry) yet with scope for improvement, the results should provide important input data for any future revision of ITS-90.

Thermodynamic-temperature data from 30 K to 200 K

New measurements of thermodynamic temperature T with Dielectric-Constant Gas Thermometry (DCGT) were performed at PTB from 50 K to 200 K. Particular care was taken to check for possible systematic sources of errors by performing experiments applying three working gases, namely helium, neon, and argon, the polarizability of which differs by a factor of up to eight. Together with former DCGT values of thermodynamic temperature the new results yield a consistent dataset in the range from 30 K to 200 K. This dataset is in good agreement with the newest results of Acoustic Gas Thermometry (AGT) and Refractive-Index Gas Thermometry (RIGT), which have quite different sources of uncertainty compared with DCGT. The combination of these DCGT, AGT, and RIGT data with the ‘Estimates of the differences between thermodynamic temperature and the ITS-90’, being as an appendix of the ‘Mise en pratique for the definition of the kelvin in the SI’ the present-day recommendation of the Consultative Committee for Thermometry, yields a new function T − T90 versus ITS-90 temperature T90 for the range from 35 K to 195 K, the uncertainty of which is reduced by a factor up to about four.

Development and Realization of Fe–C and Co–C Eutectic Fixed-Point Blackbodies for Radiation Thermometry at CSIR-NPL

A series of metal–carbon (M–C) eutectics with robust reproducible melting phase transitions are evolving as the reference high-temperature fixed-points up to 3000 °C for radiation thermometry. The mise-en-pratique prepared for the realization and dissemination of new kelvin allows the use of set of M-C blackbody fixed-points or a combination of M-C fixed-points along with silver (Ag), gold (Au) or copper (Cu) blackbodies for the direct measurement of thermodynamic temperatures at high-temperature range. The iron–carbon (Fe–C) [1153 °C] and cobalt–carbon (Co–C) [1324 °C] fixed-point cells are the doorway to high temperature above a copper fixed-point. This paper describes the in-house development of Fe–C and Co–C eutectic graphite crucible blackbodies and their realizations by linear spectral pyrometer (LP4, 650 nm) at CSIR-NPL, National Metrology Institute (NMI) of India. The novel design and assembly approaches were employed to fabricate the blackbody crucibles with 120o inner-well cone, 100 mm ingot length and 8 mm aperture diameter with 0.9997 emissivity and robust thermo-mechanical stability. The eutectic ingots were prepared by multiple fillings of the homogeneously ground and mixed powders with 4.2 and 2.6 weight percentage of carbon in Fe and Co, respectively. Repeatability of measured melting plateau and uncertainty of the temperature measurement for both Fe–C and Co–C cells are presented. The ITS-90 temperatures (T90) to these M-C fixed-points were assigned by a spectral radiance ratio measurement (Planck’s Law) relative to the freezing point of Ag [961.78 °C]. The T90 temperatures thus determined for Fe–C and Co–C blackbody fixed-point cells are 1154.05 °C and 1323.93 °C with the expanded uncertainty of 0.37 °C and 0.50 °C, respectively.

Resonance frequency measurement with accuracy and stability at the 10−12 level in a copper microwave cavity below 26 K by experimental optimization

Single-pressure refractive index gas thermometry (SPRIGT) is a novel primary thermometry technique, developed jointly by the Technical Institute of Physics and Chemistry (TIPC) of the Chinese Academy of Sciences (CAS) in China and LNE-Cnam in France. To help obtain a competitive uncertainty of 0.25 mK in thermodynamic temperature measurements, high-stability and low-uncertainty of microwave resonance frequency measurements better than 2 ppb have been demonstrated. This article describes how high-stability and low-uncertainty resonance frequency measurements were achieved using a copper microwave cavity. Microwave measurements were carried out under vacuum and isobarically at helium-4 pressures of 30, 60, 90, and 120 kPa over the temperature range of 5–26 K, with good consistency among microwave modes for the thermodynamic temperatures determined. Performance was optimized using an Allan variance analysis. In this way, with an integration time of 3 h, a stability and accuracy at the 10–12 level were obtained, an almost 20-fold improvement upon our previous result (Zhang et al 2019 Sci. Bull. 64 286–8).

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.

Relative acoustic gas thermometry setup for low temperature range from 4,2 to 80 K

Relative acoustic gas thermometry setup is described. Described setup was developed and tested in VNIIFTRI. The setup is designed for the measurement of thermodynamic temperature in low temperature range down to 4,2 K. Main part of the setup is resonator with reduced cavity diameter. Reduction of resonator dimension lead to several times reduction of cooled parts of the setup with respect to the setup previously developed in VNIIFTRI. This decreases liquid nitrogen and liquid helium consumption required for cooling of resonator. Moreover, reduction of the mass of cooling parts reduces time required for temperature stabilization and thus measurement time. In the work the tests’ results of operation of main parts of the setup are presented.

Optical Determination of Thermodynamic Temperatures from a C2H2 Line-Doublet in the Near Infrared

Is it hot in here? The recent redefinition of the kelvin unit of temperature, in terms of a fixed value of Boltzmann's constant, prompts interest in primary-standard gas thermometers that could quantify possible differences from the International Temperature Scale (ITS-90). This study reports significant progress in the development of low-uncertainty Doppler-broadening thermometry. Successful operation of a comb-calibrated near-infrared absorption spectrometer is demonstrated by probing a line doublet of acetylene. This enables the authors to make thermodynamic temperature measurements with a statistical uncertainty of less than 10 parts per million.

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.

Realization of an ultra-high precision temperature control in a cryogen-free cryostat.

Single-pressure refractive-index gas thermometry (SPRIGT) is a new type primary thermometry jointly developed by TIPC of CAS in China and LNE-Cnam in France. To realize a competitive uncertainty of 0.25 mK for the thermodynamic temperature measurement, a cryogen-free cryostat with high-stability better than 0.2 mK should be designed. This paper presented the first experimental results of temperature control for this cryostat. To realize this objective, multi-layer radiation shields combined with a thermal-resistance method were used to isolate the thermal-noise from surroundings. Besides, a new temperature control method based on a gas-type heat switch and proportional-integral-derivative control method was proposed, which was applicable to different temperature ranges by changing the working modes of the heat switch. After optimizing, the ultra-high precision temperature control in the range of 5-25 K has been fully realized, which was the temperature instability (with standard deviation) of 0.021 mK at 5.0 K, 0.05 mK at 5.7 K, 0.042 mK at 7.4 K, 0.029 mK at 14.3 K, and 0.022 mK at 25 K with the sampling time of 0.8 s. This was almost the best reporting result in the world and showed its great potential in SPRIGT.

Testing irradiance and radiance methods for absolute radiation thermometry based on InGaAs detectors in the NIR at CEM/CSIC

After measuring thermodynamic temperatures in the range from 900 °C to 2500 °C, The Centro Español de Metrologia (CEM) in collaboration with the Instituto de Óptica of the Consejo Superior de Investigaciones Científicas (IO-CSIC) are currently involved in the measurement of thermodynamic temperatures down to 400 °C using radiometers based on InGaAs detectors with central wavelengths in the near-infrared spectral range (NIR). This communication summarizes the progress towards the extension of absolute radiation thermometry measurement range to lower temperatures.

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.

Thermodynamic measurements of Zn and Al freezing temperatures using an InGaAs-based, near-infrared radiation thermometer 3 (NIRT3)

Thermodynamic temperature measurements of Al and Zn points using a near-infrared radiation thermometer 3 (NIRT3) are described. The NIRT3 was constructed for long-term stable operation, low size-of-source and characterized for linearity. The spectral responsivity was measured using tuneable near-infrared lasers and window-less InGaAs diodes. The spectral responsivity of the NIRT3 was scaled using a Au freezing-temperature blackbody and an absolute visible radiation thermometer. We then measured both the Al and Zn freezing temperatures and these measurements are compared against T-T90 values estimated by the Consultative Committee for Thermometry.