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This paper discusses the issue of the self-heating effect of resistance sensors during temperature measurement. The self-heating effect causes temperature measurement errors. The aim of this work was to develop a method for in situ assessment of the thermal resistance between a self-heating thermometer and its surrounding environment, the temperature of which is measured. The proposed method is used to assess the uncertainty resulting from the heat transfer from the thermometer to the surrounding environment, which allows increased measurement accuracy. The proposed method consists of experimental determination of the sensor’s temperature characteristics in relation to the heating power for different values of the measuring current. Sample measurements were carried out on a representative group of resistance temperature sensors. The relationship of the internal thermal resistance to the type of sensor design and the relationship of the external resistance to the ambient conditions were demonstrated. The developed method allows the appropriate measuring current of the resistance temperature sensor to be selected according to its design, the mounting method, and the environmental conditions, which ensures that measurement errors are maintained at an appropriately low level.

A calibration scheme for making oceanographic thermometers traceable to the International Temperature Scale of 1990 (ITS-90) in the range from 1 °C to 32.5 °C was established. The calibration scheme involves two phases: a first phase, in which a working reference thermometer is calibrated by comparison against an ITS-90 traceable standard platinum resistance thermometer (SPRT) in a commercial water bath, and a second phase, in which up to 24 oceanographic thermometers are simultaneously calibrated against the calibrated working reference thermometer in an ad hoc previously developed water bath. Finally, an uncertainty budget was made for both calibration phases and resulted in 1.5 mK and 3.5 mK for the first and the second phases, respectively, which satisfy the requirements of the oceanographic community for the accurate monitoring of ocean temperature.

Thermal hysteresis of platinum resistance thermometers (PRTs) was investigated in the temperature range of −196 °C to 450 °C. The wider the measured temperature range of the PRT hysteresis, the higher the observed hysteresis effect of the PRT near the mid-point of the temperature range. The magnitude of the hysteresis, defined as the difference in the resistance converted to an equivalent temperature difference between heating and cooling processes has been observed to reach up to 100 mK in PRTs used over the full temperature range. However, some PRTs did not conclusively exhibit hysteresis even in the widest temperature range, and the upper bound of hysteresis corresponded to only a few millikelvin. Clear hysteresis of the PRTs in this work was repeatable at a quantitative level, and the hysteresis of the PRTs in a wider temperature range was larger than the value linearly scaled from the measured hysteresis in a narrower temperature range. Therefore, when assessing the uncertainty associated with the hysteresis of PRTs, hysteresis should be measured in the complete temperature range of the calibration process and the calibration process should be designed so as to give a reliable estimate of the hysteresis. During the investigation of the relaxation time scale, the PRTs were intentionally undercooled below the temperature of the designated measurement point in a controlled manner to assess the impact on hysteresis. It was observed that such deviation from the prescribed treatment of the PRT during hysteresis measurement could result in an underestimation of the hysteresis. Therefore, it is best to strictly abide by the supposed direction of temperature change to accurately obtain the upper bound of the hysteresis uncertainty in a given temperature range.

The paper presents a matrix approach to the propagation of uncertainties in the realization of the ITS-90 using Standard Platinum Resistance Thermometers (SPRT) calibrated at Defining Fixed Points (DFPs). The procedure allows correlations to be included between SPRT resistances measured during the calibration at the DFPs (i.e., the realization of the ITS-90) and the resistances measured during the subsequent use of the SPRT to measure temperature . The example also shows the possible contribution of these correlations to the overall temperature uncertainty measured by a calibrated SPRT.

We studied the possibility of realizing the International Temperature Scale 1990 tin fixed point using a miniature cell and a portable temperature calibrator to improve the calibration accuracy of small high-precision platinum resistance thermometers so that it is equal to that of a Class 2 resistance thermometer. We show that the melting curves for 99.999% pure tin in a miniature cell cannot be used for this purpose. We determined the amount by which the liquidus temperature for Russian-produced commercial-grade tin is reduced due to impurities. We used the calibration methods developed in this paper to determine the optimum conditions for reproducibility of the freezing curve, and studied the properties of these curves.

Evaluation of uncertainties of the temperature measurement by standard platinum resistance thermometer calibrated at the defining fixed points according to ITS-90 is a problem that can be solved in different ways. The paper presents a procedure based on the propagation of distributions using the Monte Carlo method. The procedure employs generation of pseudo-random numbers for the input variables of resistances at the defining fixed points, supposing the multivariate Gaussian distribution for input quantities. This allows taking into account the correlations among resistances at the defining fixed points. Assumption of Gaussian probability density function is acceptable, with respect to the several sources of uncertainties of resistances. In the case of uncorrelated resistances at the defining fixed points, the method is applicable to any probability density function. Validation of the law of propagation of uncertainty using the Monte Carlo method is presented on the example of specific data for 25 Ω standard platinum resistance thermometer in the temperature range from 0 to 660 °C. Using this example, we demonstrate suitability of the method by validation of its results.

Air temperature measurements in naturally ventilated thermometer screens underpin the instrumental climate record. Increasing automation is, however, revealing limitations. One is through thermometer time response, especially in light winds or calm conditions, often at the daily temperature minimum. The exponential time response τ63 ${\\tau }_{63}$ for thermometers enclosed within a Stevenson screen is a key parameter, but poorly known. Here, τ63 ${\\tau }_{63}$ is evaluated in a practical experimental situation against the World Meteorological Organization (WMO)'s recommended sensor τ63≤20 ${\\tau }_{63}\\le 20$ s. We find τ63 ${\\tau }_{63}$ increases with sensor diameter d $d$, with only a d $d$ = 2 mm sensor meeting WMO expectations, even then requiring ambient wind speeds ≥3ms−1 ${\\ge} 3\\,\\mathrm{m}{\\mathrm{s}}^{-1}$. Typical d $d$ = 4 mm sensors never meet the criterion when either force‐ or naturally ventilated, with τ63≥20 ${\\tau }_{63}\\ge 20$ mins in a naturally ventilated arrangement under calm conditions. Inadequate τ63 ${\\tau }_{63}$ will lead to underestimation of the diurnal temperature range or other local measures derived from daily temperature maxima and minima.

The Type 1 non-uniqueness (NU-1) is the difference between interpolated values at the same temperature in the resistance thermometer subranges of the International Temperature Scale of 1990 (ITS-90) that overlap. The paper argues for a method of evaluating the NU-1 at a given temperature which considers all subranges of the Scale that contain the respective temperature, not only combinations of two, and it proposes mathematical models to determine the values of NU-1 for temperatures above 0 °C. The paper demonstrates that NU-1 is not the right contributor to the uncertainty associated with the realisation of the ITS-90. Therefore, a new concept of Correction for the Type 1 non-uniqueness of the Scale , C NU-1 , is introduced and its mathematical model is established. Also, the estimate of C NU-1 and its standard uncertainty are defined and they are assessed through statistical analysis. The values of standard uncertainty determined by the novel methodology do not exceed 0.26 mK and they are smaller than the values given in the specific Guides developed by the Consultative Committee for Thermometry. The proposed models allow authors to single out and analyse the factors that generate Type 1 non-uniqueness of the Scale and influence its value.

Single-molecule junctions have been extensively used to probe properties as diverse as electrical conduction 1 – 3 , light emission 4 , thermoelectric energy conversion 5 , 6 , quantum interference 7 , 8 , heat dissipation 9 , 10 and electronic noise 11 at atomic and molecular scales. However, a key quantity of current interest—the thermal conductance of single-molecule junctions—has not yet been directly experimentally determined, owing to the challenge of detecting minute heat currents at the picowatt level. Here we show that picowatt-resolution scanning probes previously developed to study the thermal conductance of single-metal-atom junctions 12 , when used in conjunction with a time-averaging measurement scheme to increase the signal-to-noise ratio, also allow quantification of the much lower thermal conductance of single-molecule junctions. Our experiments on prototypical Au–alkanedithiol–Au junctions containing two to ten carbon atoms confirm that thermal conductance is to a first approximation independent of molecular length, consistent with detailed ab initio simulations. We anticipate that our approach will enable systematic exploration of thermal transport in many other one-dimensional systems, such as short molecules and polymer chains, for which computational predictions of thermal conductance 13 – 16 have remained experimentally inaccessible. The thermal conductance of single-molecule junctions is measured using picowatt-resolution calorimetric scanning probes and is found to be nearly independent of the length of the alkanedithiol molecules studied.

A ferroelectric tunnelling heterostructure is presented in which both the height and the width of the tunnelling barrier can be electrically modulated, leading to a greatly enhanced tunnelling electroresistance. In Pt/BaTiO 3 /Nb:SrTiO 3 heterostructures, an ON/OFF conductance ratio that is about an order of magnitude greater than those reported in normal ferroelectric tunnelling junctions, is demonstrated at room temperature. Ferroelectric tunnel junctions (FTJs), composed of two metal electrodes separated by an ultrathin ferroelectric barrier, have attracted much attention as promising candidates for non-volatile resistive memories. Theoretical 1 , 2 , 3 , 4 and experimental 5 , 6 , 7 , 8 , 9 works have revealed that the tunnelling resistance switching in FTJs originates mainly from a ferroelectric modulation on the barrier height. However, in these devices, modulation on the barrier width is very limited, although the tunnelling transmittance depends on it exponentially as well 10 . Here we propose a novel tunnelling heterostructure by replacing one of the metal electrodes in a normal FTJ with a heavily doped semiconductor. In these metal/ferroelectric/semiconductor FTJs, not only the height but also the width of the barrier can be electrically modulated as a result of a ferroelectric field effect 11 , 12 , leading to a greatly enhanced tunnelling electroresistance. This idea is implemented in Pt/BaTiO 3 /Nb:SrTiO 3 heterostructures, in which an ON/OFF conductance ratio above 10 4 , about one to two orders greater than those reported in normal FTJs, can be achieved at room temperature 6 , 9 , 13 , 14 , 15 , 16 , 17 , 18 . The giant tunnelling electroresistance, reliable switching reproducibility and long data retention observed in these metal/ferroelectric/semiconductor FTJs suggest their great potential in non-destructive readout non-volatile memories.