RTD Accuracy Classes

Class AA, Class A, and Class B RTD tolerances

RTD accuracy class describes the tolerance of the platinum sensing element, commonly specified around IEC 60751 for Pt100 and Pt1000 sensors. The class is only one part of measurement accuracy; wiring, lead length, transmitter accuracy, immersion depth, heat transfer, and calibration method also affect the installed reading.

Thermometrics builds custom RTD assemblies using Pt100 and Pt1000 platinum elements, with Class AA, Class A, or Class B selected around the application, operating temperature range, documentation needs, and control-system uncertainty target.

When buyers ask for accuracy

  • Specify Pt100 or Pt1000 element resistance
  • Specify Class AA, A, or B
  • Confirm 2-wire, 3-wire, or 4-wire wiring
  • Confirm calibration and traceability requirements

RTD Class Comparison

RTD classCommon useGeneral selection guidance
Class AAHighest tolerance classUse when the element tolerance must be tighter and the rest of the measurement loop can justify it.
Class APrecision industrial measurementCommon choice for tighter process control, validation work, and higher confidence replacement sensors.
Class BGeneral industrial measurementCommon choice when repeatability and stability matter, but the application does not require a tighter class.

For custom assemblies, Thermometrics will review the full build: element class, sheath material, diameter, lead-wire insulation, termination, insertion length, and whether calibration documentation is required.

Pt100 vs Pt1000

Pt100 elements measure 100 ohms at 0°C and are widely used in industrial RTD probes. Pt1000 elements measure 1000 ohms at 0°C and can be useful where higher resistance improves signal handling in certain instrumentation packages.

2-wire, 3-wire, and 4-wire effects

A high-accuracy element can still read incorrectly if lead resistance is not handled properly. Use 3-wire for many industrial installations and 4-wire when lead resistance must be removed from the reading.

Immersion RTD Probes

Pt100 and Pt1000 probes with custom immersion length, sheath, fittings, and lead terminations.

View immersion RTDs

RTD Product Family

Browse RTD assemblies by installation style, including surface, sanitary, head-style, thermowell, and compact probes.

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DIN Class PDF

Download the RTD Class A/B tolerance reference PDF for engineering review.

Open PDF

Need an RTD specified to a class?

Send the temperature range, drawing, wiring, tolerance target, and documentation requirement.

Request an RTD Quote