Platinum resistance thermometers (PRTs) are widely used for accurate\ud temperature measurements in industrial process control as well as in testing and calibration\ud laboratories. Industrial-type PRTs (IPRTs) are available with platinum wires\ud of different purity and can attain measurement accuracy at the level of few tens of\ud millikelvin in a broad temperature range from −196 ◦C to 550 ◦C and above. For such\ud IPRTs, the most-used interpolation model (resistance versus temperature) is based on\ud the Callendar–Van Dusen (CVD) equation, which is also recognized in several industrial\ud standards including IEC 60751 and the corresponding national standards. In recent\ud years, several studies have shown that systematic differences exist between the ITS-\ud 90 temperature (T90) and the temperature calculated by the CVD function. When the\ud CVD equation is used to fit experimental data, the difference can be as large as several\ud tens of millikelvin, even near a calibration point, i.e., of the same order of magnitude\ud as the experimental uncertainty routinely achieved in laboratory calibrations. In order\ud to overcome the above limitations,many interpolationmodelswere proposed. The aim\ud of this work is to assess the use of ITS-90 defining equations in precision laboratory\ud calibrations of IPRTs in the temperature range from−196 ◦C to 420 ◦C. Twenty IPRTs\ud with W(100) ranging from 1.384 to 1.392 were calibrated by comparison against a\ud standard PRT, and the experimental data were processed using several interpolation\ud schemes based on ITS-90 deviation functions with different degrees of freedom. The\ud overall results showed that any ITS-90-based scheme performs better than the CVD\ud equation, suggesting that it be applied to a broad spectrum of industrial and laboratory\ud applications

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The calibration of platinum-based thermocouples from 420 • C to 1,100 • C is currently carried out at INRIM making use of two different apparatus: for temperatures below 930 • C, a potassium gas-controlled heat pipe (GCHP) is used, whereas a metal-block furnace is adopted for higher temperatures. The standard uncertainty of the reference temperature obtained in the lower temperature range is almost one order of magnitude better than in the higher temperature range. A sealed copper cell was investigated to see if it could be used to calibrate thermocouples above 930 • C with a lower uncertainty than our current procedures allowed. The cell was characterized with Type S and Pt/Pd thermocouples and with an HTPRT. The freezing plateaux were flat within 0.01 • C and lasted up to 1 h with a repeatability of 0.02 • C. The temperature of the cell was determined with a standard uncertainty of 0.04 • C. Hence, the copper cell was found to be superior to the comparator furnace for the calibration of platinum-based thermocouples because of the significant decrease in the uncertainty that it provides. An analysis was also carried out on the calibration of Pt/Pd thermocouples, and it was found that the combined use of the potassium GCHP and the Cu fixed-point cell is adequate to exploit the potential of these sensors in the range from 420 • C to 1,084 • C. A comparison with a fixed-point calibration was also made which gave rise to agreement within 0.07 • C between the two approaches.

Calibration by comparison of platinum resistance thermometers and thermocouples requires transfer media capable of providing very good short-term temperature uniformity and temperature stability over a wide temperature range. This paper describes and compares the performance of two potassium-filled gas-controlled heat pipes (GCHP) for operation over the range from 420 °C to 900 °C. One of the heat pipes has been in operation for more than 10 years having been operated at temperature for thousands of hours, while the other was commissioned in 2010 following recently developed improvements to both the design, assembly, and filling processes. It was found that the two devices, despite differences in age, structure, number of wells, and filling processes, realized the same temperatures within the measurement uncertainty. The results show that the potassium-filled GCHP provides a durable and high-quality transfer medium for performing thermometer calibrations with very low uncertainties, over the difficult high-temperature range from 420 °C to 900 °C.

Accurate heat flux measurements are needed to gain a better knowledge of the thermal performance of buildings and to evaluate the heat exchange among various parts of a building envelope. Heat flux meters (HFMs) are commonly used both in laboratory applications and in situ for measuring one-dimensional heat fluxes and, thus, estimating the thermal transmittance of material samples and existing buildings components. Building applications often requires heat flux measurements below 100 W center dot m(-2). However, a standard reference system generating such a low heat flux is available only in a few national metrology institutes (NMIs). In this work, a numerical study aimed at designing an HFM calibration apparatus operating in the heat flux range from 5 W center dot m(-2) to 100 W center dot m(-2) is presented. Predictions about the metrological performance of such a calibration system were estimated by numerical modeling exploiting a commercial FEM code (COMSOL(A (R))). On the basis of the modeling results, an engineered design of such an apparatus was developed and discussed in detail. The system was designed for two different purposes: (i) for measuring the thermal conductivity of insulators and (ii) for calibrating an HFM with an absolute method (i.e., by measuring the applied power from the heater and its active cross section) or by a relative method (i.e., by measuring the temperature drop across a reference material of known thickness and thermal conductivity). The numerical investigations show that in order to minimize the uncertainty of the generated heat flux, a fine temperature control on the thermal guard is needed. The predicted standard uncertainty is within 2% at 10W center dot m(-2) and within 0.5% at 100 W center dot m(-2)