round of thermodynamic temperature measurement of fixed points has been completed at NIM and comp...

Start Date

Jan, 2008

End Date


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Radiometric Measurement of Thermodynamic Temperature



NIM is developing an absolute radiation thermometer to determinate the temperature of metal-carbon eutectic points. The metal-carbon eutectic points are considered as  candidates of new fixed points in high temperature.


The first round of thermodynamic temperature measurement of fixed points has been completed at NIM and was with PTB. The difference of T measurement between PTB and NIM is within 0.2 K. Now NIM joins the T value determination of the HTFPs and will start the measurement by 2013.


Description & Major Accomplishments

A concerted international project was launched to assign thermodynamic temperatures to high temperature fixed points (HTFPs) within radiation thermometry working group of Consultative Committee for Thermometry (CCT-WG5). The thermodynamic temperature measurement techniques together with the characteristics of HTFPs, form an important basis to implement the MeP-K. At National Institute of Metrology (NIM), China, the studies on HTFPs and radiometric measurements of thermodynamic temperature have been started since 2004 and 2007, respectively.


The hybrid method, by introducing a lens to irradiance mode, was adopted at NIM to measure the thermodynamic temperature. The parts of concern, including the objective lens, the front aperture and the filter radiometer of the absolute radiation thermometer (ART) were kept in an area with a constant temperature created by a water cycling thermostat. All of physical elements which affect temperature measurement were analyzed and calibrated.


The absolute radiation thermometer was established with two alternative filter radiometers (633nm and 900nm). The parameters of the absolute radiation thermometer were calibrated. The thermodynamic temperatures of silver fixed point and Co-C, Pt-C, Re-C were determined. The uncertainties were 0.24K to 0.94K for FR633 and 0.34K to 1.6K for FR900 from the silver point to Re-C. The results were compared with the ITS-90 values and showed a good agreement: 0.18K at Co-C, -0.11K at Pt-C and -0.24K at Re-C, which are under the uncertainties estimated.