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Above the freezing point of silver (961.78 °C), the International Temperature Scale of 1990 is defined in terms of Planck’s radiation law. The scale is maintained and disseminated using a validated and linear pyrometer in conjunction with a blackbody reference source at either the Ag, Au (1064.18 °C) or Cu (1084.62 °C) freezing point. In order to realize the scale with the highest precision high quality, well‐characterised, reproducible fixed‐point blackbody sources are required. Such sources have been maintained at NPL for a number of years, but it was felt that improvements to the design would be beneficial. A new Ag point blackbody source has therefore been constructed. The new design will improve the quality and reproducibility of the melting and freezing plateaux and reduce errors due to the ‘out‐of‐focus’ size‐of‐source effect which is difficult to measure and to eliminate. Full details of the design of the new …
HIMERT
(2003)
Metal‐carbon eutectic mixtures show much promise for high‐temperature standards applications. A research project, Novel, High temperature, Metal‐carbon Eutectic fixed points for Radiation Thermometry, Radiometry and Thermocouples (HIMERT) was accepted by the European Union (submitted under the Framework 5 Growth Programme) with a view to developing a unified European approach to these standards. The objectives of the project are to develop fixed‐point cells both for radiation thermometry/radiometry and contact thermometry calibration applications. In total three sets of cells will be developed, two for radiation thermometry (by BNM‐INM and NPL) and one for contact sensors (by BNM‐LNE) and comparisons performed of the differing crucible designs. The cells developed for radiation thermometry will be calibrated according to the ITS‐90 and measured radiometrically by a third participant (PTB …
The Physikalisch-Technische Bundesanstalt (PTB) has developed dedicated instrumentations and methods for the traceable calibration of space borne instruments in terms of the three fundamental radiometric units, i.e. spectral radiance (radiation temperature), spectral radiant intensity and spectral photon flux. The traceable calibration under conditions similar to the space environment is achieved by use of two major radiometric calibration facilities of PTB, the Spectral Radiance Comparator Facility (SRCF) and the Reduced Background Calibration Facility (RBCF) which are part of the Primary Temperature Radiator Facility of PTB and cover the wavelength range from the UV to the FIR (THz range). The improved detector instrumentations of the SRCF and RBCF, detailed calibration schemes and results of calibrations for space missions are presented.
Gas sensors based on a semiconductor-supported LaF3/Pt-structure require regular re-activation by thermal treatment. A convenient way to accomplish this is by applying an electrical current pulse to the Pt-electrode and controlling re-activation by the amount of Joule heat deposited. Pulse length has to be chosen to balance the requirements of thermal energy needed for re-activation and the constraints in peak thermal power to prevent damage. Prerequisite to optimization is a knowledge of the thermal response of the complicated thin film sensor system consisting of several layers with unknown thermal properties. Modulated photothermal microscopy was used to detect inhomogenities in thin film heating and early stages of failure under thermal load. It was found that the formation of gas bubbles in the film is one of the major sources of failure. These measurements were complemented by measurements of …
The thermodynamic temperatures of the phase transition of Re-C, TiC-C, and ZrC-C eutectic fixed-point cells have been measured for the first time using different filter radiometers in irradiance mode. The spectral responsivity of these filter radiometers was measured traceable to the primary detector standard of the PTB, a laser based cryogenic radiometer. The relative extended uncertainties of the spectral responsivities of the filter radiometers in the irradiance mode were in the range from 5· 10-4 up to 2.5· 10-3. The measurements have been performed at the high temperature calibration facilities of the VNIIOFI and the PTB with eutectic fixed-point cells manufactured by VNIIOFI.
The intercomparison of radiation temperature scales between PTB and NMIJ was carried out in September 2001. PTB sent their radiation thermometer LP3 to Japan and NMIJ made the comparison between the LP3 and NMIJs Topcon radiation thermometers with a comparison blackbody from 1000/spl deg/C to 2500/spl deg/C. Both scales agreed within /spl plusmn/0.8/spl deg/C in the whole range.
The large area double-heatpipe blackbody (LABB) used for comparing thermodynamic temperatures with the International Temperature Scale of 1990 (ITS-90) at temperatures higher than 600 C is based on two sodium heat pipes. The lowest temperature at which the sodium heat pipes work properly is strongly correlated to the onset of sodium evaporation. This is expected for temperatures well above 500 C. Planning to use the LABB for extending the comparison of thermodynamic temperatures with the ITS-90 to temperatures as low as possible, we measured the isothermal behaviour of the blackbody cavity starting at heatpipe temperatures of 400 C. The temperature of the cylindrical part of the cavity was measured with a standard platinum resistance thermometer (SPRT) sensing the bottom of the cavity and up to three quarter of the cylindrical part of the cavity. The obtained temperature profiles are well explained assuming the occurrence of two superimposing effects: a real nonisothermal behaviour of the LABB for temperatures below 500 C and a cooling of the SPRT caused by radiation loss through the aperture of the cavity. Applying a Monte-Carlo simulation we calculated the emissivity of the LABB at different heatpipe temperatures below 600 C using the obtained non-isothermal temperature distribution at the cylindrical walls. It was found that even at temperatures as low as 415 C the accuracy of the LABB is sufficient for comparison of thermodynamic temperatures and the ITS-90.
For the sake of ensuring improved accuracy and traceability for temperature measurements above the copper point (1084 OC), four laboratories are joining their efforts in developing high-temperature fixed points based on eutectic transitions of metal-carbon mixtures [1]. These phase transitions, on the basis of radiation thermometry results presented thus far [2, 3], encouraged the participants to work towards two eventual applications: hightemperature fixed—point calibration sources for radiation thermometry, and fixed points for the calibration of contact thermometers, including Pt/Pd, Pt/Rh and W/Re thermocouples.
Here will be given the up-to—date works accomplished within or in relation with this project in the participating laboratories. The perspectives of this work are wide and should allow the usage of such fixed points at temperatures ranging from 1150 C to 2700 C. The remaining uncertainty concerns the …
An advanced method for the calibration of tungsten strip lamps is reviewed in detail. The method is based on measuring the ratio of the spectral radiances of two sources at different radiance temperatures TL by radiation thermometry. Instead of using the distribution temperature and the colour emissivity for the calculation of the radiance temperature, the derivative dTL/dλ in the vicinity of the effective wavelength of the detection system is applied. In a first step high-stability vacuum tungsten strip lamps are calibrated as first-order working standards with respect to fixed points of the International Temperature Scale of 1990 (ITS-90). In a subsequent step, secondary working standards are calibrated relative to these first order working standards with light of different wavelengths determined by interference filters. A detailed description of the evaluation procedure for the determination of the radiance temperature of the lamps is given and several problems encountered in operating the lamps are discussed. The standard uncertainties of the radiance temperature are below 0.2 K for the first order working standards.