Improved Interpolating Equation for Industrial Platinum Resistance Thermometer

산업용 백금저항온도계를 위한 향상된 내삽식

  • Yang, In-Seok (Division of Physical Metrology, Korea Research Institute of Standards and Science) ;
  • Kim, Yong-Gyoo (Division of Physical Metrology, Korea Research Institute of Standards and Science) ;
  • Gam, Kee-Sool (Division of Physical Metrology, Korea Research Institute of Standards and Science) ;
  • Lee, Young-Hee (Division of Physical Metrology, Korea Research Institute of Standards and Science)
  • 양인석 (한국표준과학연구원 기반표준본부) ;
  • 김용규 (한국표준과학연구원 기반표준본부) ;
  • 감기술 (한국표준과학연구원 기반표준본부) ;
  • 이영희 (한국표준과학연구원 기반표준본부)
  • Received : 2011.09.28
  • Accepted : 2011.12.09
  • Published : 2012.03.31


We propose an improved interpolating equation to express temperature-resistance characteristics for modern industrial platinum resistance thermometers (PRTs). Callendar-van Dusen equation which has been widely used for platinum resistance thermometer fails to fully describe temperature characteristics of high quality PRTs and leaves systematic residual when the calibration point include temperatures above $300^{\circ}C$. Expanding Callendar-van Dusen to higher-order polynomial drastically improves the uncertainty of the fitting even with reduced degrees of freedom of the fitting. We found that in the fourth-order polynomial fitting, the third-order and fourth-order coefficients have a strong correlation. Using the correlation, we suggest an improved interpolating equation in the form of fourth-order polynomial, but with three fitting parameters. Applying this interpolating equation reduced the uncertainty of the fitting to 32 % of that resulted from the traditional Callendar-van Dusen. This improvement was better than that from a simple third-order polynomial despite that the degrees of the freedom of the fitting was the same.


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