About this service

The Consultative Committee for Thermometry (CCT) is one of the Consultative Committees of the International Committee for Weights and Measures (CIPM). It coordinates thermometry research and provides internationally-agreed reference data for temperature scales and measurements. The reference data sets included in this service are sourced from documents related to the Mise en pratique for the definition of the kelvin in the SI, to support the realization of scale temperatures via the International Temperature Scale of 1990 (ITS-90) and Provisional Low Temperature Scale of 2000 (PLTS-2000), and the realization of thermodynamic temperature via primary radiometric measurements and acoustic gas thermometry.

Available data

• ITS-90 Scale:
  • SPRT acceptance criteria at the Ag, Ga and Hg points
  • fixed-point temperature values, and variation with depth and pressure
  • ³He and ⁴He vapour pressure temperature values and equation coefficients
  • fixed-point isotopic corrections for deuterium in e-H₂, ²²Ne and ²¹Ne in Ne, and ¹⁷O and ¹⁸O in H₂O
  • e-H₂ vapour pressure temperature values near 17 K and 20.3 K
  • SPRT reference function and inverse function coefficients, reference function W_r values and first derivative, and inverse function temperatures
• PLTS-2000 Scale:
  • ³He melting pressure equation coefficients and reference arrays (Arrays 1–4)
  • melting pressure of ³He
  • derivative of melting pressure of ³He
• Primary radiometric temperature measurement:
  • blackbody spectral radiance
  • geometric factor equations and uncertainty
  • integrated transmittance and mean wavelength
  • high-temperature fixed point thermodynamic temperatures
  • radiation constants c₁ and c₂
  • uncertainty budget components and examples
• Acoustic gas thermometry:
  • sensitivity of squared speed of sound to specific impurities
  • second acoustic virial coefficient of Ar

User feedback

Comments, questions, and suggestions regarding this service are welcome. Feedback may be submitted through either of the following channels:

• GitHub Issues (a free GitHub account is required): Open an issue
• Email: Users without a GitHub account may send their feedback to Patrick Rourke (CCT Working Group on Digitalization, Chair) or Cristhian Paredes (BIPM Liaison Officer for Digital Transformation), who will register it on their behalf.

The International Temperature Scale of 1990 (ITS-90) realizes scale temperature T₉₀ that is an approximation to thermodynamic temperature T in the range from 0.65 K and above.

Available data

• SPRT acceptance criteria at the Ag, Ga and Hg points
• fixed-point temperature values, and variation with depth and pressure
• ³He and ⁴He vapour pressure temperature values and equation coefficients
• fixed-point isotopic corrections for deuterium in e-H₂, ²²Ne and ²¹Ne in Ne, and ¹⁷O and ¹⁸O in H₂O
• e-H₂ vapour pressure temperature values near 17 K and 20.3 K
• SPRT reference function and inverse function coefficients, reference function W_r values and first derivative, and inverse function temperatures

• Fixed-point temperatures
• He vapour pressure coefficients
• SPRT reference function coefficients

Primary radiometric thermometry realizes thermodynamic temperature T via the Planck law, which relates T to the spectral radiance of an ideal blackbody. It may be applied as either absolute primary thermometry (T measured directly, in terms of the definition of the base unit kelvin) or relative primary thermometry (T measured indirectly, relative to one or more fixed points of known thermodynamic temperature).

Available data

• blackbody spectral radiance
• geometric factor equations and uncertainty
• integrated transmittance and mean wavelength
• high-temperature fixed point thermodynamic temperatures
• radiation constants c₁ and c₂
• uncertainty budget components and examples

• High-temperature fixed points
• Radiation constants

Primary acoustic gas thermometry realizes thermodynamic temperature T via the relationship between T and the speed of sound in an ideal gas in the limit of zero frequency. It may be applied as either absolute primary thermometry (T measured directly, in terms of the definition of the base unit kelvin) or relative primary thermometry (T measured indirectly, relative to a fixed point of known thermodynamic temperature).

Available data

• sensitivity of squared speed of sound to specific impurities
• second acoustic virial coefficient of Ar

• Sensitivity of squared speed of sound