ITS-90
The International Temperature Scale of 1990 ( International Temperature Scale of 1990 : ITS-90 ) was established in 1989 by the International Committee for Weights and Measures ( CIPM adopted). It defines temperatures in the units Kelvin and degrees Celsius and supports the comparability and compatibility of temperature measurements. It is needed because measuring the thermodynamic temperature using a primary thermometer is very complicated and time-consuming. In contrast, the temperature determination with secondary thermometers is easier. However, these must be calibrated, which the ITS-90 enables.
construction
The ITS-90 defines from 0.65 K up to the highest measurable temperatures, the temperatures in Kelvin and in degrees Celsius, which only represent a (as good as possible) approximation of the real thermodynamic temperature. For this purpose, the ITS-90 defines special temperatures, so-called fixed points (mostly temperatures of certain phase transitions of some substances), which were determined in the past with a primary thermometer. Defined thermometers are used to interpolate (very rarely also extrapolated ) between these temperature values , which were previously calibrated at the fixed points . The scale is divided into individual areas in which a certain interpolation thermometer is prescribed. The individual temperature ranges overlap and thus lead to an inherent ambiguity in the scale, since different processes and different fixed points usually do not result in exactly the same temperatures.
To cover the whole range, you need:
- Helium vapor pressure thermometer from 0.65 to 5 K,
- Helium gas thermometer from 3.0 to 24.5561 K,,
- Platinum resistance thermometer from 13.8033 to 1234.93 K,
- Spectropyrometer above 1234.93 K,
The specified values (the fixed points) on which the ITS-90 is based only reflect the status from 1990 and can be refined in a future ITS-XX scale. The interpolation formulas and even the thermometric procedures can also be adapted, just as the ITS-90 is only a further development of its predecessors, the IPTS-68 and the EPT-76 (low temperature range). Just as historical precision measurements can be converted into one another today, the ITS-90 ensures the traceability of temperature data in our time for the future, which absolute methods cannot (yet) achieve.
For lower temperatures, the ITS-90 is supplemented by the provisional low temperature scale from 0.9 mK to 1 K ( Provisonal Low Temperature Scale from 0.9 mK to 1 K , PLTS-2000).
Fixed points
The following table shows the fixed points on the scale.
fixed point | Temperature ( K ) | Temperature ( ° C ) |
---|---|---|
Triple point of hydrogen | 13.8033 | −259.3467 |
Triple point of neon | 24.5561 | −248.5939 |
Triple point of oxygen | 54.3584 | −218.7916 |
Triple point of argon | 83,8058 | −189.3442 |
Triple point of mercury | 234.3156 | −38.8344 |
Triple point of water | 273.16 | 0.01 |
Melting point of gallium | 302.9146 | 29.7646 |
Melting point of indium | 429.7485 | 156.5985 |
Melting point of tin | 505,078 | 231,928 |
Melting point of zinc | 692.677 | 419,527 |
Melting point of aluminum | 933,473 | 660,323 |
Melting point of silver | 1234.93 | 961.78 |
Melting point of gold | 1337.33 | 1064.18 |
Melting point of copper | 1357.77 | 1084.62 |
In the range between 3 K and 5 K (−270.15 ° C to −268.15 ° C) no fixed points are used, but the vapor pressure of helium.
Web links
- International temperature scale from 1990
- Overview of the history of the temperature scales ( Memento from December 1, 2006 in the Internet Archive )
- Differences between ITS-90, EPT-76 and IPTS-68 (English) (PDF; 139 kB) (this and other documents here ) (PDF file; 136 kB)
- Conversion of temperature values on different international scales; Equations and algorithms.
- Calculation example ITS-90 characteristic curve
literature
- Walter Blanke: The international temperature scale from 1990: ITS-90 . Ed .: Physikalisch-Technische Bundesanstalt . Wirtschaftsverlag NW, Verlag für Neue Wissenschaft, Braunschweig [u. a.] 1989, ISBN 3-89429-040-4 .
Individual evidence
- ↑ a b c d Joachim Seidel, Jost Engert, Bernd Fellmuth, Joachim Fischer, Jürgen Hartmann, Jörg Hollandt, Erich Tegeler: The International Temperature Scales ITS-90 and PLTS-2000 . In: PTB-Mitteilungen . tape 117 , no. 3 , 2017, p. 16-22 .
- ^ A b c d e Walter Blanke: The new "International Temperature Scale of 1990" . In: Physics in Our Time . tape 22 , no. 1 , 1991, p. 13-19 .