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Research paper : Improving the reliability of temperature measurements taken with clinical infrared ear thermometers (J. Ishii)−52−Synthesiology - English edition Vol.1 No.1 (2008) industrial standard (technical standard document). Here, direct traceability to national standard is maintained for radiance temperature measured by the ear thermometer. For radiance temperature scale, existing calibration service is not yet organized as in contact thermometers, so the government must take some responsibility for design and establishment of new traceability system for ear thermometers. However, if it becomes possible for AIST to provide direct calibration service of radiance temperature scale of working standard BBR, the clinical thermometer manufactures will be able to make the uncertainty estimation of the calibration and conformity assessment, without necessarily having advanced technology or knowledge for the structure or operation of working standard BBR, because they can rely on the high technological expertise of AIST (the government). Also, the manufacturers may develop their own technology including working standard BBR, and may be able to utilize the equipment they currently own. Therefore, this method was adopted because in current technological and social situation, the cost to the government can be minimized while maintaining high reliability of ear thermometers .5 Development of national standard for radiance temperatureUrgent issue for AIST after choosing the measurement management system described in Section 4.3, was the development of national standard for radiance temperature, which will serve as the primary standard for the ear thermometer. It would be preferable if results of these technical developments can also be used widely in performance tests including calibration of ear thermometers in industry.Conventional mercury-in-glass and electronic clinical thermometers are contact thermometers in which the sensor probe is placed in contact with the human body site to reach thermal equilibrium state to measure the temperature. Therefore, they can be calibrated or assessed by placing them in a thermostatic fluid bath using high-precision liquid-in-glass thermometer or platinum resistant thermometer as a reference thermometer. Also, evaluation of uncertainty of calibration and management of calibration equipment can be done relatively easily.In contrast, ear thermometer is an infrared radiation thermometer that measures radiance in the infrared wavelength region and estimates body temperature based on Planck’s law. Therefore, it is technically impossible to directly compare temperature scale against contact thermometer such as liquid-in-glass or platinum resistant thermometers. Calibration and assessment of infrared radiation thermometer must be conducted against standard “blackbody radiator (blackbody furnace)” that generates ideal thermal radiation (blackbody radiation) according to Planck’s law. The authors have been working on the development and characterization for high-precision blackbody radiation source in room temperature region, and they started the development of standard BBR especially for calibration of ear thermometer based on these elemental technologies.Figure 4 shows the standard BBR for calibration of ear thermometer developed by AIST. High-precision platinum resistant thermometer was employed as standard of temperature scale (reference thermometer), and metal blackbody cavity was installed horizontally in precise thermostatic water bath. When standard BBR realized the radiance temperature scale, the components of uncertainty could be classified as follows:(1) Uncertainly of calibration of reference thermometer(2) Uncertainty of cavity temperature measurement by reference thermometer(2)-1 Uncertainty of temperature measurement of water in bath(2)-2 Difference between measured temperature of water and temperature of inner surface of cavity (heat loss effect of cavity)(3) Effective emissivity of blackbody cavity (difference from ideal value 1)(3)-1 Cavity emissivity of blackbody cavity under isothermal conditionFig. 4 Standard BBR for calibration of ear thermometer developed by AIST (external appearance and cross sectional view)Fig. 5 Evaluation of effective emissivity of blackbody cavity by Monte Carlo simulationCalibration work of ear thermometer(a) Blackbody cavity (b) Reference thermometer (c) Heater element (d) Cooling coil (e) Stirrer (f) Thermal insulation wall(a)(e)(d)(c)(b)(f)~~Temperature value at position where n-th light ray was reflected k times : T(n,k)n-th incident lightAmbient temperatureθ : Field-of-view of ear thermometerStochastic determination of reflection direction using random numbersReference temperature of blackbody cavity :T0Intrinsic emissivity of inner wall of blackbody cavity : αBlackbody cavityTambientT(n,1)

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