Vol.1 No.1 2008

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Research paper : Improving the reliability of temperature measurements taken with clinical infrared ear thermometers (J. Ishii)−50−Synthesiology - English edition Vol.1 No.1 (2008) In general, ear thermometer manufactured by companies is calibrated against the working standard BBR available in the company. The working standard BBR is also calibrated against the higher level standard BBR, and this standard BBR is traceable to national standard for temperature with high-precision contact thermometer. Practical BBR for body temperature range requires a reference thermometer to accurately determine the temperature of blackbody cavity, and a high-precision platinum resistance thermometer (PRT) can be used. For this PRT sensor, calibration system (traceability system) based on the national standard in AIST had already been established and is actually in operation. Using this traceability system, it is possible to calibrate the temperature scale at sufficiently small uncertainty level of less than 0.01 °C for the reference thermometer.If the goal value of uncertainty of clinical thermometer reading is 0.2 °C, the uncertainty of working standard BBR, which will be used for calibration and assessment for clinical thermometer of a manufacturer should be approximately 1/3 or less (in this case 0.07 °C or less) of uncertainty for the clinical thermometer. Moreover, the higher-level standard BBR must have even smaller uncertainty (for example, 0.04 °C or less) than the working standard BBR of the manufacturer.Next, various technical works are necessary at each phase of a chain of calibration as shown in Figure 3, and a choice must be made on which sector will be responsible for these works. As shown in the lower part of Figure 3, after careful comparative review of the three potential measurement management systems, the system that matched the current technological and social situations was selected.(1) Testing and inspection are done based on verification scheme of the Measurement Law (measurement management system in which verification of all products is conducted under government authority through law enforcement).(2) Traceability of manufacturers’ working standard BBR to national standard for temperature (high-precision standard PRT sensor at AIST) is required by industrial standard, and specification of working standard BBR is also established by industrial standard (measurement management system totally dependent on autonomous activity of manufacturers in industry).(3) The government (AIST) provides new calibration service for radiance temperature scaleTerm 7, while traceability to AIST radiance temperature standard is established by industrial standard for manufacturer’s working standard BBR (measurement management system in which responsibility is shared by government and manufacturers in industry).The following discussion and selection were done for each of the above measurement management systems.4.1 Measurement management system based on verification of Measurement LawThe Measurement Law in Japan designates measuring instruments that are particularly important to economic activities and services as “specified measuring instrument”, and also requires a pattern approval test for structure and specification of the measuring instrument as well as a test of instrumental error for each measuring instrument. In case of clinical thermometer, conventional mercury-in-glass and electronic thermometers have been manufactured and sold after being designated as specified measuring instruments by the Measurement Law. Under the measurement Fig. 3 Traceability and measurement management system of ear thermometerLevel of uncertaintyEar thermometerBlackbody radiator for ear thermometer (working standard BBR)Standard blackbody radiator (standard BBR)High-precision contact thermometer (platinum resistant thermometer, etc.)National standard for temperature (temperature fixed points, etc.)Choice①Choice②Choice③Verification by GovernmentActivity by manufacturer through industrial standardsCalibration service by GovernmentActivity by manufacturer through industrial standardsCalibration service by Government±0.2 ℃±0.001 ℃±0.01 ℃±0.04 ℃±0.07 ℃

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