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)−54−Synthesiology - English edition Vol.1 No.1 (2008) the two BBRs was measured using the high-resolution ear thermometers. Comparison measurements were repeated about 10 times for each thermometer, and after evaluating the average and variance of radiance temperatures, the temperature difference of reference thermometer was corrected and the calibration results were calculated.Figure 6 shows the results of the verification experiment. The average values of radiance temperature differences of the two BBRs were almost zero within the range of variation. However, the variation (standard variation) of calibration values was around 0.03 °C. This variation in value was uncertainty factor that occurred additionally in radiance comparison calibration of the BBR. From these results, approximately 0.06 °C (95 % confidence level) was obtained as uncertainty of calibration result in combination of uncertainty of radiance temperature scale of the national standard BBR with the uncertainty of direct comparison measurement with ear thermometers with high resolution mode[11]. This uncertainty satisfied the uncertainty level required for calibration of working standard BBR (approximately 0.07 °C or less).6.2 Verification of uncertainty of calibration by collaborative experiment with manufacturers Joint measurement experiment was conducted by AIST and ear thermometer manufacturers to verify the uncertainty level estimated in the simulated calibration experiment as mentioned in the previous section, as well as the validity of the proposed calibration scheme. For this round robin experiment, AIST constructed a standard BBR that could be transported. The standard BBR was transported to seven Japanese thermometer manufacturers by commercial carrier, and the differences with radiance temperatures of working standard BBRs of the companies were measured by the direct comparison method mentioned above.Figure 7 shows the measurement results[14]. The results of the comparison measurements at each manufacturer have variations of about 0.03 °C, but it was confirmed that the radiance temperature scale of working standard BBR of each company agreed with the standard BBR of AIST within 0.05 °C. This showed that the radiance temperature of working standard BBR of thermometer manufacturers could be calibrated at uncertainly of 0.07 °C or less, and it was concluded that requirement for calibration and assessment of ear thermometer was met sufficiently based on this traceability scheme.7 Calibration service system and verification of international equalityIn establishing traceability system, along with development of national standard and dissemination of temperature scale, an important issue is to verify whether the Japanese national standard and calibration service are equivalent to those of other countries. For this purpose, quality management system in accordance with ISO/IEC 17025 standardTerm 8 was organized for calibration service of working standard BBR for ear thermometer conducted at AIST. By operating the quality management system, the quality of calibration service can be maintained based on third party approval.To verify equivalence of the national standard developed by AIST to the national standards of other countries, international comparison measurements were conducted among national metrology institutes of Germany and United Kingdom. Figure 8 shows the result of the international comparison measurement conducted between Physikalisch-Technische Bundesanstalt (PTB) of Germany and National Physical Laboratory (NPL) of the UK[15]. The standard BBRs of AIST and PTB were transported to NPL, and radiance temperature scales were compared directly. From the Fig. 6 Verification result for calibration of radiance temperature scale of working standard blackbody furnace against national standard BBR at AISTFig. 7 Result of round-robin comparison measurement of working standard BBRs of clinical thermometer manufacturers with AIST standard BBR Blackbody temperature is 37 °C. A~G are participating manufacturers.BCDEFGA-0.10.10.050-0.05Radiance temperature difference in AIST standard BBR / ℃Preset value of blackbody temperature / ℃Radiance temperature difference of calibrated BBR from standard BBR / ℃403735-0.2-0.10.00.20.1

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