RTD and Thermocouple Tolerance Class Calculator
Find the maximum permitted deviation of a sensor at a given temperature for its tolerance class: IEC 60751 for platinum RTDs and IEC 60584-1 for thermocouples.
- IEC 60751: tolerance = a + b × |t| for each class
- All classes for this sensor are listed in the table below.
Tolerance at 200 °C
| Class | Valid range | Tolerance |
|---|---|---|
| AA (wire wound) | −50 to 250 °C | ± 0.44 °C |
| A (wire wound) | −100 to 450 °C | ± 0.55 °C |
| B (wire wound) | −196 to 600 °C | ± 1.3 °C |
| C (wire wound) | −196 to 600 °C | ± 2.6 °C |
| AA (film) | 0 to 150 °C | outside range |
| A (film) | −30 to 300 °C | ± 0.55 °C |
| B (film) | −50 to 500 °C | ± 1.3 °C |
Tolerance Class Formulas
Thermocouple K (IEC 60584-1): Class 1 ±1.5 °C or ±0.004|t|, Class 2 ±2.5 °C or ±0.0075|t|, whichever is greater
t is the temperature in °C. RTD classes apply over ranges that differ for wire wound and thin film elements. Thermocouple tolerances apply to the wire as supplied; they do not include drift, installation or instrument errors.
Worked example
At 200 °C a Class A RTD may deviate ±0.55 °C and Class B ±1.3 °C. A Class 1 type K thermocouple at 600 °C may deviate ±2.4 °C.
Frequently Asked Questions
What is the difference between Class A and Class B RTDs?
Class A has less than half the permitted error of Class B, ±(0.15 + 0.002|t|) against ±(0.3 + 0.005|t|), and a narrower valid range.
Which thermocouple class should I specify?
Class 1 for better accuracy where available; Class 2 is the standard grade. Class 3 covers sub zero temperatures for some types.
Do these tolerances include drift?
No. They are initial tolerances. Thermocouples in particular drift with time at high temperature.
Learn more on the blog
Thermocouple and RTD installation precautions
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
Read Full Article