Vol.3 No.1 2010

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Research paper : Improving the reliability of temperature measurements up to 1550 ℃ (M. Arai et al.)−36−Synthesiology - English edition Vol.3 No.1 (2010) point, Cu fixed point, Co-C eutectic point, and Pd fixed point are 0.09 °C, 0.11 °C, 0.53 °C, and 0.79 °C, respectively. This is the highest-level calibration capacity in the world, as described in the following section.4.4 Element 4: Equivalence of the national measurement standard by international comparison To investigate whether the realized fixed point was in accordance to the national measurement standards of other countries, an international comparison (APMP-T-S1-04) was conducted among the national metrology institutes of the Asia-Pacific region. Type R thermocouples were circulated among the participating institutes, each institute calibrated the type R thermocouple with their temperature fixed points, and the calibration values were compared with the value of the pilot laboratory. There were 12 national metrology institutes that participated: National Measurement Institute (NMIA) (Australia); National Institute of Metrology (NIM) (China); Standards and Calibration Laboratory (SCL) (Hong Kong); National Physical Laboratory (NPLI) (India); Research Center for Calibration, Instrumentation and Metrology, Indonesian Institute of Sciences (KIMLIPI) (Indonesia); Korea Research Institute of Standards and Science (KRISS) (Korea); Standards and Industrial Research Institute of Malaysia (SIRIM) (Malaysia); Standards, Productivity and Innovation Board (SPRING, currently NMC A*STAR) (Singapore); Council for Scientific and Industrial Research (CSIR, currently NMISA) (South Africa), National Metrology Institute of Japan (AIST/NMIJ); Center for Measurement Standards (CMS) (Taiwan); and National Institute of Metrology (Thailand) (NIMT) (Thailand).Figure 17 shows the comparison result at 1084.62 °C, the freezing point of copper, and the differences of the calibration value between of the participating institutes and NMIA, which was the pilot laboratory, are presented with the calibration uncertainties of each institute. The calibration uncertainty of AIST/NMIJ was the smallest-level among the participating institutes, and it was confirmed that the calibration value at the Cu fixed point matched almost completely at the level of uncertainty claimed by other countries. The comparison of the calibration value at the Ag fixed point was conducted in the same international comparison, and as with the Cu fixed point, the calibration uncertainty of the Ag fixed point by AIST/NIMJ was the smallest-level, and the calibration values of each country matched almost completely at the uncertainty level claimed by them[18].For the Co-C eutectic point, AIST/NMIJ joined the Euromet Project 857[19], a joint project of Physikalisch-Technische Bundesanstalt (PTB) (Germany), National Physical Laboratory (NPL) (UK), and Laboratoire Commun de Métrologie (LNE-Cnam) (France) that are the major European national metrology institutes. As the result of an international comparison in which Pt/Pd thermocouples and the Co-C eutectic cells were circulated, good agreement was obtained[20].4.5 Element 5: Constructing and operating the quality managing system for thermocouple calibration Based on the quality management system for the calibration and testing service conducted by AIST, a technical manual of the calibration service for thermocouples was generated in 2004. To meet the requirements of the ISO/IEC 17025, the international standard for the calibration and testing laboratories, the particulars of personnel, facility and environmental condition, calibration method, equipment, traceability, handling of the calibrated device, reporting, and others were determined. According to this manual, the calibration would be conducted and the calibration records would be in safekeeping. The evaluation method for the drift and inhomogeneity that are uncertainty sources unique to the calibration of thermocouples were described in detail, Table 1 Calibration uncertainty of the thermocouples at each temperature fixed point.Temperature of fixed point / ℃Temperature fixed point used for calibrationTransfer standards961.78Agfixed point1084.621324.0Co-C eutectic point1553.5Pd fixed pointType R thermocouplePt/Pd thermocouplesUncertainty of measurement system / ℃0.0210.0190.0180.042The combined standard uncertainty is the combination of individual uncertainty components, and is given by the positive square root of sum of squares of the uncertainties of the components.Cufixed pointUncertainty of fixed point realizing device / ℃Uncertainty of thermocouple itself / ℃Combined standard uncertainty of calibration / ℃(Level of confidence of approx. 68 %)Expanded uncertainty of calibration / ℃(Level of confidence of approx. 95 %)0.0140.0340.0420.090.0210.2600.2310.0450.0600.3150.0540.2670.3930.110.530.791.61.20.80.40.0-0.4-0.8-1.2-1.6NMIANIMSCLNPLIKIMLIPIKRISSSIRIMSPRINGCSIRAIST/NMIJCMSNIMTLAB-PILOT / ℃Fig. 17 The result of international comparison of the calibration value of type R thermocouple at the Cu fixed point (1084.62°C). indicates the difference between the calibration values of the participating institutes and NMIA, and the error bar indicates the calibration uncertainty of each institute.

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