Pt100 tolerance classes explained (IEC 60751)

IEC 60751 specifies the resistance–temperature relationship for industrial platinum resistance thermometers (R₀ = 100 Ω, α = 0.003851 /°C) and the tolerance classes. The tolerance grows with |t| because the deviation from the nominal curve accumulates away from 0 °C.

Worked values

• At 0 °C: AA ±0.10, A ±0.15, B ±0.30 °C.
• At 100 °C: AA ±0.27, A ±0.35, B ±0.80 °C.
• At −40 °C: AA ±0.17, A ±0.23, B ±0.50 °C.

Using the class in a budget

For an uncalibrated sensor, the class tolerance is a rectangular Type B limit. For a calibrated sensor the class is irrelevant: the certificate's correction and uncertainty apply. A Class B sensor calibrated at the points of use can be a perfectly good 0.05 °C instrument — until it drifts.