PT100 platinum resistance thermometers are the standard element for high-accuracy temperature measurement in industry. Dry block calibrators are indispensable devices for calibrating these sensors both in the field and in the laboratory.
How a Dry Block Calibrator Works
A dry block calibrator precisely heats and cools a metal block containing holes. The probe to be calibrated and the reference probe are placed in the same block and exposed to the same temperature. The difference between the readings is reported as the PT100’s deviation.
Critical Parameters
- Block temperature distribution (radial and axial): the temperature difference between holes is typically 0.05 °C–0.2 °C
- Stabilisation time: after reaching the set point, wait a minimum of 20–30 minutes
- Immersion depth: at least 15 times the probe diameter must be immersed (otherwise conductive error occurs)
- Reference probe class: must be at least 4 times more accurate than the probe being calibrated
Application Steps
- Ambient conditions are checked (20 ± 3 °C, 45–75% RH)
- The reference probe is placed in the calibrator at least 1 hour beforehand for stability
- The calibration points are selected (e.g. −20, 0, 50, 100, 200, 400 °C)
- After 30 minutes of stabilisation at each point, 10 readings are taken
- The difference between the reference and the DUT is reported together with the uncertainty
Field tip
Widening the calibrator holes with an adapter improves radial temperature distribution. Use the original adapter for each sensor diameter.
Uncertainty Components
Typical uncertainty components in PT100 calibration: the reference probe uncertainty, the readout instrument uncertainty, block temperature distribution, stability, resolution and repeatability. All components must be combined using the GUM method.