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Research paper−47−Synthesiology - English edition Vol.1 No.1 (2008) In the 1990s, a U.S. company developed a new infrared clinical thermometer in which measurement was taken by inserting the sensor probe into the ear canal (hereinafter will be called “ear thermometer”), and was marketed in the United States and Europe. Figure 1 shows the external appearance of ear thermometers and the schematic diagram of the measurement principle. Ear thermometer consists of optical probe, infrared sensor, compensating internal temperature sensor, signal processing circuit, and display unit. The tip of the optical probe is inserted into the ear canal, the intensity (radianceTerm 1) of infrared radiation at around 10 µm wavelength emitted from eardrum and skin surface of inner ear canal is measured, and the temperature of measured part is determined from the relation of Planck’s law of thermal radiationTerm 2. The calibration of temperature reading is conducted by using the ear thermometer to measure the radiation from ideal blackbody cavity for which accurate temperature is known.The human skin surface has emissivityTerm 3 close to unity in the thermal infrared wavelength region, so it is a suitable object for infrared radiation thermometry. The method of measuring skin surface temperature from thermal radiation measurement has been also applied successfully to breast cancer diagnosis technology using thermograph. In newly developed ear thermometers, eardrum and surrounding ear canal were selected as cavity to be measured, and therefore effective emissivity () of the measured area approached the condition of almost ideal blackbody (=1), and the accuracy of body temperature measurement was greatly improved. Also, measurement could be accomplished in a short time of about 1 second by introducing advanced infrared sensor technology. This ear thermometers overcame the issues of conventional contact type (thermal equilibrium type) clinical thermometer, and drew attention as third-generation clinical 1 IntroductionAlong with blood pressure and heart rate, body temperature is one of the most basic vital signs of the human body that is used for medical diagnosis and health management. Since body temperature measurements are taken at home as well as in medical institutions by physicians and nurses, clinical thermometers require high reliability and utility as measuring instrument.Mercury-in-glass thermometers have been used for a long time, but there were problems of glass breakage and use of mercury that is harmful to the human body. Later, when high-precision thermistor was developed as temperature sensor, clinical electronic thermometers with thermistor sensors became commercially available, and its use spread rapidly due to ease of handling and safety. It is widely used to this day. However, there were still problems with clinical electronic thermometers since the sensor must be held close to measured body-site such as the armpit for around five minutes to measure the body temperature accurately making it unpractical for emergency patients in serious condition, and temperature measurement in newborns and infants were difficult.- Design and establishment of a new calibration system traceable to the national standards -Juntaro IshiiMetrology Institute of Japan, AIST Tsukuba Central 3, Tsukuba, Ibaraki 305-8563, Japan E-mail : j-ishii@aist.go.jpInfrared ear thermometer was developed and rapidly spread in Japan in the late 1990’s, but users began to question the reliability of the temperature readings. AIST developed a new national standard for the calibration and conformity assessment of new ear thermometers, and also designed and organized the traceability system, conducted technological verification, and improved reliability of measured temperature, to meet the demands of Japanese industry and consumers. An international comparison of national measurement standards among Germany, UK, and AIST was conducted and the equality of the standards was experimentally verified to maintain international reliability.Improving the reliability of temperature measurementstaken with clinical infrared ear thermometersKeywords : Standard, traceability, infrared, clinical thermometer, reliability, blackbody, radiance temperatureFig. 1 External appearance and structure of ear thermometerEardrumInfrared radiationEar canalOptical probeInfrared optical sensorSignal processing circuitInternal temperature sensorSurface temperature value is determined as quasi blackbody cavity37.0 ℃Display[Translation from Synthesiology, Vol.1, No.1, p.47-58 (2008)]

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