project is for the redetermination of the Boltzmann constant by the fixed-path-length cylindrical...

Start Date

Dec, 2006

End Date


  • +86-(0)10-64526172 Dr.Zhang Jintao
  • Leader Contact Thermometry Lab

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Redetermination of the Boltzmann Constant by the Fixed-Path-Length



Based on NIM’s developed primary standard pyrometer, an improved scheme, an "fixed-point blackbody – pyrometer" assembly, was applied to realize and disseminate International Temperature Scale of 1990 (ITS-90) above the silver point. The new scheme can correct the drifts of the pyrometer and extend the highest measurable temperature from 2200℃ to 2474℃. The expanded uncertainties of the scale were (0.08 - 0.62) ℃ between a temperature range of (961.78 - 2474) ℃.


Description & Major Accomplishments

The high temperature primary standard system was improved gradually at NIM after 2005. A new primary standard pyrometer (PSP) has been developed, with a size-of-source effect less than 1×10-4 and a distance effect around 1×10-4. The interference filters, photoelectric detector and amplifier applied in the PSP are temperature-controlled respectively. A relative spectral responsiveness calibration facility has been improved. An LED-based nonlinearity measurement facility has been established. They are employed for characterizing the PSP. The fixed point blackbody - pyrometer assembly is utilized to maintain the International Temperature Scale of 1990 above the silver point. This scheme can avoid influence of the instability and inhomogeneity of tungsten strip lamps and correct the drift of the pyrometer. The expanded uncertainties of the scale realization are 0.04°C at the silver point and 0.48 °C at 2474 °C. The uncertainties of the temperature scale are evaluated and proved by international comparisons of high temperature points’ ITS-90 values among China, the UK and Spain in 2009.