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Temperature Measurement · Glossary

What is ITS-90?

International Temperature Scale of 1990Temperature Measurement

ITS-90 is the International Temperature Scale of 1990, which defines temperature by fixed points and standard interpolating instruments.

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ITS-90 Explained

ITS-90 sets temperatures of defining fixed points such as the triple point of water (273.16 K) and the freezing points of tin, zinc and silver. Between them, standard platinum resistance thermometers interpolate.

Calibration laboratories realise ITS-90, and plant calibrations trace back to it through reference thermometers and dry blocks.

ITS-90: Typical Values

Triple point of water273.16 K (0.01 °C)
Freezing point of tin231.928 °C
Freezing point of zinc419.527 °C
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Calculators for ITS-90

CalculatorPt100 TableFree online calculator with formula and worked example.CalculatorThermocouple TableFree online calculator with formula and worked example.

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Frequently Asked Questions

What is ITS-90?

ITS-90 is the International Temperature Scale of 1990, which defines temperature by fixed points and standard interpolating instruments.

Why do thermocouple tables refer to ITS-90?

The reference functions in IEC 60584-1 and NIST tables are based on ITS-90 temperatures.

Will ITS-90 be replaced?

Metrology bodies review it periodically; it remains the scale in use.

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