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Characterized IEC 60751 models

Use IEC60751RTDModel when you have an IEC 60751 PT-385 platinum RTD whose reference resistance at 0 °C has been individually characterized.

A nominal Pt100 uses R0 = 100 Ω. A particular probe might instead have a measured or certified value such as 100.017 Ω. Keeping that real R0 can make the model represent the individual probe more closely while retaining the standard PT-385 curve shape.

Example: characterized Pt100

from rtd_sensor.models import IEC60751RTDModel

probe = IEC60751RTDModel(
    r0_ohms=100.017,
    name="Calibrated probe A",
    minimum_temperature_c=-50.0,
    maximum_temperature_c=250.0,
)

temperature_c = probe.resistance_to_celsius(119.42)

Example: characterized Pt1000

The class is not limited to nominal 100 Ω sensors:

from rtd_sensor.models import IEC60751RTDModel

probe = IEC60751RTDModel(
    r0_ohms=1000.24,
    name="Characterized Pt1000",
    minimum_temperature_c=0.0,
    maximum_temperature_c=180.0,
)

The curve is still IEC 60751 PT-385; only the reference resistance and declared range differ.

Why declare a range?

A calibration or application may justify a narrower interval than the complete IEC characteristic. The model enforces the range you declare so downstream code does not silently use the characterization outside its intended scope.

Defaults are available for the full IEC range, but for an individually characterized sensor it is usually better to record the range actually supported by the source or calibration.

What this model does not mean

Providing a characterized R0 does not by itself prove that a physical probe conforms to every IEC 60751 construction, tolerance, or test requirement. It is a numerical model of the PT-385 characteristic with your selected reference resistance.

Fit R0 from calibration observations

For rtd-sensor 0.7.0, rtd_sensor.fitting.fit_iec60751_r0() estimates R0 from one or more temperature/resistance calibration observations while holding the PT-385 characteristic fixed. It returns an IEC60751RTDModel plus separate immutable fit evidence. An explicitly declared model range describes intended applicability and need not contain the observation temperatures; the evidence retains the actual observation span independently.

This is different from fitting arbitrary Callendar–Van Dusen coefficients: the standard curve shape is assumed, and only its reference-resistance scale is estimated.

Portable deployment

IEC60751RTDModel is supported by the versioned portable model-definition format, so a characterized model can be serialized and reconstructed without repeating the characterization process.