Thermocouple types and tolerance classes (IEC 60584)
Types K, J, T, N, E and the noble-metal types R, S, B each have defined EMF curves and tolerance classes 1, 2 and 3. Choose by range, environment and required tolerance.
- Type K (NiCr–NiAl): −200 to 1250 °C; general purpose; subject to ordering effects at 250–600 °C.
- Type N (NiCrSi–NiSi): more stable than K at high temperature.
- Type T (Cu–CuNi): −200 to 350 °C; best low-temperature performance among base metals; Class 1 ±0.5 °C or 0.4 %.
- Type J (Fe–CuNi): −40 to 750 °C; iron leg oxidises.
- Type E (NiCr–CuNi): highest output; −200 to 900 °C.
- Types R, S (Pt–PtRh): to 1600 °C; laboratory reference use.
- Type B (PtRh–PtRh): to 1700 °C; negligible output below 50 °C.
Tolerance classes are for new wire; a thermocouple used in a steep gradient develops inhomogeneity that no calibration corrects. For precise low-temperature work, a PRT is nearly always the better choice.
Frequently asked questions
- Why is Type T preferred for freezers and cold rooms?
- Its tolerance is tightest at low temperatures, it is stable in moist conditions, and the copper leg has low resistance — all useful in −80 to +50 °C applications.
References
- [1]IEC 60584-1:2013 — Thermocouples, Part 1: EMF specifications and tolerances
General technical guidance written against the cited sources. It is not regulatory or legal advice and does not replace the applicable standard, guideline or a qualified reviewer's judgement.
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