Vol.3 No.1 2010

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Research paper : Improving the reliability of temperature measurements up to 1550 ℃ (M. Arai et al.)−37−Synthesiology - English edition Vol.3 No.1 (2010) and the procedure for quantitatively evaluating the effects on the calibration value and uncertainties of the thermocouple was also described in the technical manual. In May 2006, the calibration service of the thermocouples by AIST was certified to be in accordance to the international standard under the certification program provided by the National Institute of Technology and Evaluation (NITE). The quality management system is the element that is necessary to regularly maintain the technique, where the calibration method for the thermocouples was established by careful evaluation of uncertainty and then verified by international comparison. It raises the reliability of thermocouple calibration conducted by AIST both domestically and internationally.5 Element 6: Establishment of the traceability system5.1 Design of the traceability system for thermocouplesThe traceability system for temperature was constructed based on the JCSSTerm 4 system according to the “Measurement Act” in Japan. In this traceability system, the national measurement standards are used to calibrate transfer standards of the calibration laboratories which calibrate thermometers used in industry. As the national measurement standards, the fixed-point devices for the Ag fixed point (in 2002), the Cu fixed point (in 2002), and the Pd fixed point (in 2005) of AIST were designated as national primary standards by the Measurement Act. By following this Act, AIST provides the transfer standards with calibration values at these three points as the standards to the calibration laboratories [21][8]. The calibration laboratories calibrate their temperature scales by transferring the standard from the transfer standards to their fixed-point devices. However, for the Pd fixed point, the laboratories are allowed to select the method of transferring the standard by comparison calibration to working standard thermocouples instead of their fixed-point devices.The transfer standards calibrated by AIST are the secondary standards as designated by the Measurement Act, and Pt/Pd thermocouples were employed for the Ag and the Cu fixed points and a type R thermocouple for the Pd fixed point. By providing the standard at the Pd fixed point using the thermocouple as the transfer standard, as shown in Fig. 18, calibration laboratories are now able to have the temperature standards up to 1554 °C for the working standard thermocouples, and to calibrate various thermocouples including the type R thermocouple using their working standard. Currently, AIST conducts approximately 10 calibrations a year for the secondary standards using the national primary standards, and issues the calibration certificates with the “jcss” mark designated by the Measurement Act to indicate that they were calibrated using the national primary standards.Apart from the jcss calibration, AIST started the provision of the temperature standard at Co-C eutectic point upon request in 2009[7]. This enabled a more accurate verification of the temperature scale created by the calibration laboratories.The calibration laboratories registered to the JCSS can flexibly select various calibration services according to their own equipment, including the calibration of various fixed-point devices up to the Cu fixed point, fixed-point calibration up to the Cu fixed point for noble metal thermocouples (types R, S, B, and Pt/Pd), base metal thermocouples (types N, K, E, J, and T), and thermometers with indicators for high temperature range, as well as the comparison calibration of thermometers at temperature range to a maximum of 1554 °C[22]. 5.2 Joint research with Japanese calibration laboratories and drafting of the technical documentsTo disseminate the Pt/Pd thermocouple as the standard thermocouple, the parties took a circulating test of the Pt/Pd thermocouple from June 2001 to March 2002 in the working group of the Temperature Measurement Subcommittee, under the 36th Committee on Industrial Instrumentation of the Japan Society for the Promotion of Science. With the objective of assessing the drift of thermocouples during calibration at the Cu fixed point, four Pt/Pd thermocouples were fabricated under the same condition from platinum and palladium wires taken from the single lot, and were subjected to tests. These thermocouples were transferred from “AIST four labs AIST,” and after conducting recovery annealing, they were sent to “AIST remaining Fig. 18 Diagram of the traceability system of thermocouples for high temperature range (as of February 2010).thermocouplethermocouplethermocoupleJapan Calibration Service SystemUserSecondary standardsNational primary standardsPdCuAg JCSS 0.2 ℃~2 ℃Pt/PdPt/PdPt/PdType RType ROther type thermocouples, etc.AISTCalibration labjcss 0.09 ℃0.79 ℃0.11 ℃Co-CPd-CCo-C0.53 ℃Type R or S thermocouplefixed pointfixed pointfixed pointeutectic pointeutectic pointOrdered measurement calibrationthermocouplethermocoupleeutectic pointPdCuAg fixed pointfixed pointfixed point

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