Measurement uncertainty in temperature mapping results
A mapping conclusion — the space is within 2–8 °C — carries the loggers' calibration uncertainty, their resolution and any drift since calibration. Compare the extremes plus uncertainty with the limits.
Mapping reports frequently present minimum and maximum temperatures to two decimals and compare them with limits as if they were exact. A logger with U = 0.3 °C reading 7.9 °C is consistent with 8.2 °C at the product. Whether that matters depends on the acceptance criteria and the decision rule — but it should be stated.
Components for a mapped position
- Logger calibration uncertainty at the nearest calibrated point.
- Drift or as-found error at the post-study check, if performed.
- Resolution of the logger.
- Response-time effects, if the logger is buffered differently from the acceptance criterion's intent.
ValiTrac's mapping engine records each logger's calibration data alongside its statistics so the acceptance evaluation can include uncertainty explicitly rather than by silent omission.
Frequently asked questions
- Should mapping acceptance criteria be widened to allow for uncertainty?
- No — product limits are fixed. The decision rule states how uncertainty is treated; a guard band tightens the internal acceptance, it does not loosen the product limit.
References
- [1]JCGM 100:2008 — Guide to the expression of uncertainty in measurement (GUM)
- [2]ILAC-G8: Guidelines on Decision Rules and Statements of Conformity
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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Combine Type A and Type B components per the GUM: divisors by distribution, sensitivity coefficients, u_c, effective degrees of freedom and U at k = 2.
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Setting acceptance criteria for a mapping study
Acceptance criteria come from the product's storage condition, expressed as limits, a permitted excursion definition, and a rule for what happens at the boundary.
What is a decision rule and why every certificate needs one
A decision rule states how measurement uncertainty is accounted for when declaring pass or fail against a tolerance. Simple acceptance, guard banding and non-binary statements are the common choices.