IEC 60751 tolerance classes

IEC 60751 defines temperature-dependent tolerance classes for platinum RTDs. rtd_sensor.tolerance calculates the numerical maximum permitted temperature deviation for those classes and enforces the class validity ranges.

Tolerance is a conformity limit, not automatically a standard uncertainty.

Complete thermometer

For an assembled thermometer or probe:

from rtd_sensor import tolerance

maximum_error_c = tolerance.thermometer_tolerance_c(
    100.0,
    tolerance_class="A",
    construction="wire_wound",
)

print(maximum_error_c)  # 0.35

A result of 0.35 means a nominal tolerance band of ±0.35 °C at 100 °C. It does not predict that the sensor will actually be off by 0.35 °C.

Thermometer classes are AA, A, B, and C. Construction is either "wire_wound" or "film", because the standard validity range depends on construction.

Bare platinum resistor

For a bare sensing resistor:

maximum_error_c = tolerance.platinum_resistor_tolerance_c(
    100.0,
    tolerance_class="F0.15",
)

The ASCII class designation includes construction: W for wire-wound and F for film. Supported designations are W0.1, W0.15, W0.3, W0.6, F0.1, F0.15, F0.3, and F0.6.

Range enforcement

The same formula cannot be extended indefinitely and still carry the same IEC class designation. If the requested temperature is outside that class's standard validity range, the function raises ValueError.

What this function does not prove

Calculating a class limit does not establish that a physical device satisfies all IEC 60751 construction, qualification, and testing requirements. The API provides the numerical tolerance rule and its valid range.

Tolerance versus uncertainty

If you choose to use a tolerance bound as an input to an uncertainty budget, you must also choose and justify a probability model. For example, treating a bound as rectangular is a user modeling assumption, not something IEC 60751 states automatically.

See Uncertainty fundamentals.