The calibration of gradient heat flux sensors

Test benches for calibrating heat flux sensors at temperatures of 500–1000 K are described, and the results of such calibrations are presented.     

Modernized state primary standards of the units of thermal quantities

The content and results of efforts to modernize the three State Primary Standards of the units of temperature in the 0–3000°C range and also of the standards of thermal conductivity and coefficient of linear expansion of solids, stored at the Mendeleev Research Institute of Metrology, are described. It is shown that, simultaneously with the modernization of the standards, the systems of transmitting the dimensions of the units of the standards to working measuring instruments have also been improved.     

Measurement of Al Freezing-Point Temperature: Effect of Initiation Process

In CCT documents it is stated that “...for the freezing curves of the metallic fixed points, the maximum observed temperature on the plateau should be taken as the best approximation of the liquidus temperature. The fixed points should be realized with the inner and outer liquid-solid interfaces and extend past the maximum by 10 % to 20 % of the fraction frozen, to clearly establish the value of the maximum and the resolution of its determination.” Also, it is accepted that “...the inner interface is essentially static. It is the temperature of the inner liquid/solid interface that is measured by the thermometer.” The analysis of freezing curves obtained by the standard method of fixed-point realization shows that the parameters of the initial part of the freezing curve, the mean temperature value of which is usually taken as the liquidus temperature, depend on how the inner interface is initiated. Variations in the duration and intensity of initiation cause changes in the initial part of the freezing curve and in the resulting SPRT measurement. Moreover, the relation between the duration of the initial section of the plateau with a minor temperature change and the duration of its final section with a significant slope also depend on the initiation method used and on the furnace temperature. The effect of freezing initiation conditions on the measurement result is individual for each fixed point because of the differences in thermophysical properties of metals and in conditions of the heat transfer from the liquid–solid interface to the thermometer. Aluminum has a maximum value of the melting specific heat in comparison with other metals used in ITS-90 fixed points; in the present study, the effect of the intensity and duration of the inner liquid–solid interface initiation was investigated both experimentally and through calculation.     

The standard function for a platinum resistance thermometer above the setting point of silver

A method and apparatus are described for measuring the characteristics W(T) at 962– 1085 °C for a hightemperature platinum resistance thermometer. A special design has been used containing a radiating cavity of black-body type localized around the sensitive element. The measurements were made with a spectropyrometric comparator by brightness comparison at the Ag, Au, and Cu reference points, and also at temperatures representing multiple and fractional brightnesses. The results are compared with the W(T) obtained by interpolating measurements made by the contact method at the Zn, Al, and Cu reference points. The differences in the W(T) constituted the temperature equivalent of 0.16, – 0.14, and 0.04 at the reference points correspondingly for Ag, Au, and Cu. The over- all measurement error is estimated as 0.19°C. An interpolation formula is proposed that is based on the standard function W_ref(T₉₀) given in the definition of ITS- 90.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 39–42, September, 1993.     

Conception of metrological assurance for monitoring environmental thermal pollution

Sources of environmental thermal pollution are considered in regard to the scale of their impact on the entire planet and on the ecological situation of individual regions and the life of people in enclosed premises. The main principles are formulated for the conception of metrological assurance in monitoring environmental thermal pollution. Translated from Izmeritel'naya Tekhnika, No. 12, pp. 29–31, December, 1997.     

Temperature at the Reference Points of Scale MTSh-90

It is shown that the lack of a clear definition of one of the main concepts underlying temperature scales – the reference-point temperature – is causing uncertainty in the realization of the temperatures corresponding to the reference points on scale MTSh-90. An analysis is made of the advantages and disadvantages of different approaches to determining the temperature at reference points. It is proposed that this temperature be the temperature at which a given substance of a specified degree of purity begins to crystallize. That temperature corresponds to thermodynamic equilibrium of the liquid phase having the specified initial concentration of impurities.     

Intercomparison of the Realization of the ITS-90 at the Freezing Points of Al and Ag among European NMIs

The EUROMET.T-K4 comparison is the regional extension of CCT-K4, an intercomparison of the realizations of the freezing points of Al (660.323°C) and Ag (961.78°C). The intercomparison was organized in four loops. Long-stem standard platinum resistance thermometers (SPRTs) were used as traveling standards: 25 Ω thermometers to be used only at the Al freezing point and two high-temperature standard platinum resistance thermometers (HTSPRTs) to be used only at the Ag freezing point in each loop. Parallel to the measurements with thermometers, the pilots and sub-pilots organized an internal intercomparison using an Ag fixed-point cell. Most HTSPRTs showed a strong drift which is mainly due to mechanical stress and poisoning of the sensor by impurities. This drift can be partially compensated by a correction based on Matthiessen’s rule. An evaluation of the data taking into account both HTSPRTs in each loop, the linkage of the sub-pilots by measurements at the Ag freezing point, and a possible compensation according to Matthiessens’s rule, allows calculation of the results of the participants’ measurements at the Ag freezing point. The results of the participating laboratories are summarized, and proposals for key comparison reference values and linking of the results to CCT-K3 and CCT-K4 are presented.