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Research paper : Improving the reliability of temperature measurements taken with clinical infrared ear thermometers (J. Ishii)−49−Synthesiology - English edition Vol.1 No.1 (2008) standard was established by American Society for Testing and Materials (ASTM)[6], while national measurement standard system was slow to develop. In Europe, the preparation was in progress for the European Norm (EN)Term 5 lead by Germany that was center for major manufacturers[7] of ear thermometers. In Germany, Physikalisch-Technische Bundesanstalt (PTB), a national metrology institute, actively engaged in the technical development of measurement standards for ear thermometers.3 Setting research goals and scenario for achievementAs issues to be tackled by AIST described in the previous section, establishment of traceability system for ear thermometers to satisfy user demand was set as a goal, and it was also desirable to utilize the results of technical development obtained in the process of achieving the research goal for performance assessment of ear thermometers. Specifically, 0.2 °C (95 % confidence level) was set as the technical goal for uncertainty of temperature readings (measurement result) in ear thermometers at a commercial level. Since the maximum permissible error for measurement methods for mercury-in-glass and clinical electrical thermometers was set at 0.1 °C, some users requested 0.1°C uncertainty for ear thermometer. However, estimating the currently existing technical level of ear thermometers on market, and considering the fact that 0.2 °C uncertainty was employed in drafts of the industrial standards[6, 7] in the US and Germany, the Survey and Research Committee for New Clinical Thermometer concluded that the goal for Japan should be 0.2 °C[2].To achieve this goal, AIST considered the necessary essential technology and scenario as shown in Figure 2. Research goals of AIST were set as follows: (1) development of performance test technology for conformity assessmentTerm 6, (2) development of calibration technology for radiance temperature scale of ear thermometers for accuracy management, and (3) establishment of national primary standard for radiance temperature scale that serves as basis of traceability system. To meet these goals, AIST started “the development of high-precision blackbody radiator (standard blackbody furnace)” as a common and key technology. In the development of blackbody radiator (BBR), elemental technologies were designated as follows: (A) technology for precise thermostatic fluid bath needed to realize stable and uniform temperature field, (B) technology for quantitative assessment of radiant property of blackbody cavity, and (C) design and manufacture technology to realize optimal blackbody cavity for calibration of ear thermometers.4 Adoption of measurement management system for JapanFigure 3 shows how temperature scale of ear thermometers leads to the national primary standard via chain of calibrations (the traceability system) from the viewpoint of technical practicability. There were major technologies to be developed in each phase of traceability, and an issue was to whom the responsibility for the technical work at each phase would be assigned in the social system of metrological management. For calibration and assessment of ear thermometer, which is based on the principle of infrared radiation thermometry, BBR emitting ideal blackbody radiation traceable to correct temperature scale was necessary. The main component of BBR is a reference thermometer that provides standard temperature scale and a blackbody cavity that is a source of thermal radiation and a thermostatic fluid bath. Therefore, we considered what should be the most appropriate system under which each component could be managed to control the quality of the BBR.Fig. 2 Research goal and scenario for improving reliability of ear thermometersClinical thermometer manufacturersAISTElemental technologyResearch goalConsumers, medical personnelImproved instrument performance of ear thermometer・ Higher sensitivity・ Stability against environmental temperature・ Compensation of characteristic variation in infrared sensor element・ Improvement of durability and mechanical shock resistanceDesign and construction of thermostatic water bath・ Stability and uniformity of cavity temperature・ Accurate measurement of cavity temperatureEvaluation of effective emissivity of blackbody cavity・ Monte Carlo simulation・ Consideration of specular-diffuse reflection・ Measurement of intrinsic emissivity of cavity wall material・ Temperature distribution of cavity wallDesign and construction of blackbody cavity・ Design of cavity with high effective emissivity・ Design of cavity for instrument with wide view anglesDevelopment of ear thermometerDevelopment of conformity assessment technologyDevelopment of calibration technologyDevelopment of national standardUser’s demand for clinical thermometersEstablishment of technical standards, JIS for ear thermometersEstablishment of traceability system for ear thermometersImproved reliability of ear thermometer

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