Liquid bath versus dry-block calibrator
A stirred liquid bath offers the best uniformity; a dry block offers speed, portability and no fluid — the choice is about uncertainty and practicality.
Both generate a stable temperature for comparison calibration. A stirred liquid bath surrounds the probe with a well-mixed fluid, giving excellent uniformity and low immersion error. A dry-block calibrator heats a metal block with drilled wells; it is faster and cleaner but has axial and radial gradients that must be characterised.
Choose a bath when
- The lowest uncertainty is needed.
- Probes are odd shapes or short, where well fit is poor.
- Several probes must be compared simultaneously under identical conditions.
Choose a dry block when
- Calibration is on site or at many locations.
- Fluids are unacceptable (cleanliness, safety, temperature range).
- Probes are long, straight and fit the wells with minimal clearance.
Either way the medium's contribution to uncertainty — stability, uniformity, immersion — belongs explicitly in the budget.
Frequently asked questions
- What uncertainty can a dry block achieve?
- With an external reference and characterised gradients, roughly 0.05–0.2 °C at k = 2 depending on temperature and probe fit; the block's display alone is not a reference.
- Can a dry block be used for short probes?
- With caution: short immersion means stem conduction and the block's axial gradient contribute large errors. A bath or a block with a shallow-well insert designed for the probe is preferable.
References
- [1]EURAMET cg-13: Calibration of Temperature Block Calibrators
General technical guidance written against the cited sources. It is not regulatory or legal advice and does not replace the applicable standard, guideline or a qualified reviewer's judgement.
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