Vol.1 No.1 2008

61/76

Research paper : Improving the reliability of temperature measurements taken with clinical infrared ear thermometers (J. Ishii)−57−Synthesiology - English edition Vol.1 No.1 (2008) Discussion with reviewers1 Future technological issues for improving reliability of ear thermometersQuestion (Akira Ono)The point that excels in this paper is that it describes not only a technological development, but is a comprehensive discussion that also addresses balance of social systems such as verification, calibration service, and industrial standards.I think the traceability system established according to the result of this study is satisfying to keep the tolerance of ear thermometers to ±0.2 °C. On the other hand, what is the level of long-term stability for the ear thermometers themselves?Also, which points do you think need R&D in the future to keep the tolerance to ±0.2 °C or less for commercial ear thermometers? I would like to hear the author’s view on both technological development of thermometer and technological development of measurement standard.Answer (Juntaro Ishii)At AIST, an examination of long-term stability and reproducibility of several commercially available ear thermometers in the market were conducted by periodical calibration over one and a half year against the standard BBR of AIST in 1999. The results showed that most ear thermometers have long-term stability of approximately 0.2 °C or less, and some ear thermometers go over 0.2 °C in the period of about half a year, and in some the temperature scale change was as great as 0.4 °C (Figure a shows the results). It is difficult to specify the cause of the long-term instability, but in general, they are due to the drift of infrared sensor responsivity, the change in characteristic of compensation temperature sensor, and the deterioration of the performance of the optical element.If the goal is to keep the tolerance of the commercial ear thermometer to 0.2 °C or less, I think it is necessary to employ design and specification that can maintain the long-term stability of at least one year against the standard BBR, and this should be the technological development goal of the ear thermometer by manufacturers.Moreover, for the metrological control of clinical thermometers used in medical institutions, regular performance check about once a year may be effective, in addition to the initial assessment when products are shipped out. For such a regular check, it is necessary to develop and spread a practical BBR calibrator that can be used at medical institutions and thermometer dealers.Also, as discussed in the paper, the uncertainties that occur during the calibration of working standard BBRs by the comparison measurement method are relatively large (variation is about 0.03 °C by standard deviation) in the present traceability scheme of radiance temperature, and we are aware that it is difficult for the thermometer manufacturer to conduct hierarchical organization of working standard BBRs within the company. For this, I think a technological development is necessary for conducting radiance comparison measurement at smaller uncertainty using standard BBRs. Until now, commercial high-resolution ear thermometers were applied as a radiance comparator, but currently, we are working on the development of high-performance infrared radiation thermometer with small measurement variation compared to the ear thermometers, and are obtaining good experiment results toward realization of the radiance comparison measurement at smaller uncertainly of around 0.01 °C.2 Other methods for calibration of working standard BBRQuestion (Akira Ono)I think as a method for calibrating working standard BBRs of thermometer manufacturer against national standard BBR of AIST, there is a method of using infrared ear thermometer itself as the transfer (traveling) standard, other than a direct comparison of blackbody cavities described in the article. Also, I think there is a method of removing the blackbody cavity from the working standard BBR of thermometer manufacturer, transport it to AIST, and calibrate against the standard BBR. How do you evaluate such calibration methods compared to the direct comparison method?Answer (Juntaro Ishii)Figure b shows the transfer standards and calibration schemes for realizing traceability of radiance temperature scale.・On method of using ear thermometer as a transfer standardUsing ear thermometer as a transfer standard will reduce the cost of transportation compared to a larger BBR system, and for manufacturers, there is a merit that it is relatively easy to calibrate several working standard BBRs using the transfer standard thermometer in the house. However, since the standard radiance temperature scale is realized and maintained on ear thermometer which will serve as a transfer standard, superior transport stability and long-term stability shall be required in addition to the basic performance such as the temperature resolution.AIST conducted experimental verification for calibration scheme of using ear thermometer as a transfer standard along with direct comparison scheme by transporting BBR. According to the experiment, in the scheme using thermometer as transfer standard, the level of variation of calibration increased to 0.05 °C~0.1 °C. This large variation occurred due to the level of stability and reproducibility of ear thermometer during traveling, Fig. a Long-term stability of temperature scale of commercial ear thermometersFig. b Options of transfer standardMeasurement periodInstrumental error / ℃2001/51999/101999 Oct.~2001 May±0.2 ℃-0.6-0.2-0.40.00.20.40.6Working standard BBR(Installed at manufacturer’s factory)CalibrationCalibrationCalibrationStandard BBR (national standard)(Installed at AIST)Transport of blackbody cavityReturn of blackbody cavityTransport of a set of ear thermometersReturn of a set of ear thermometersTransport of BBRReturn of BBR

※このページを正しく表示するにはFlashPlayer9以上が必要です