4. What is class A and class B?

In the world of RTDs (Resistance Temperature Detectors), platinum has gained enormous popularity. This is due to the physical characteristics that make it superior to other materials for sensing temperature.

To provide interchangeability between manufacturers for the sake of global industry, there are some international standards that have been adopted by most countries:

  • IEC 60751 defines the temperature accuracy and the resistance/temperature characteristic curve for several tolerance classes
  • “Class B” and “Class A” are the most common tolerance classes.

These are defined by a single nominal resistance/temperature characteristic curve and the following accuracy designations:

Tolerance Class Tolerance (°C) Wire-wound construction* Thin-film construction*
B ±(0.3 + 0.005|t|) -196 to 600°C -50 to 500°C
A ±(0.15 + 0.002|t|) -100 to 450°C -30 to 300°C

*Consult sensor manufacturer for sensor construction of a particular model

There are a number of standards that either copy or are predecessors of IEC 60751. Among them are IEC 751, DIN 43760, EN 60751, and BS EN 60751. Another standard, ASTM E1137, uses the same nominal characteristic curve, but defines tolerances differently, and designates them as “Grade B” and “Grade A”. The ASTM standard is not used as widely as the IEC standard.

Visit our RTD calculator to generate your specific temperature table.

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