ISO 27893:2011

Overview

ISO 27893:2011 - "Vacuum technology - Vacuum gauges - Evaluation of the uncertainties of results of calibrations by direct comparison with a reference gauge" - gives guidance for determining and reporting measurement uncertainty when calibrating vacuum gauges by direct comparison with a reference gauge (per ISO/TS 3567). The standard ensures uncertainties are calculated and reported uniformly so that reported uncertainties are transferable and can be reused as components in subsequent uncertainty assessments.

Key topics

• Measurement models: Defines two primary models that cover most practical calibrations:
  • Sum model - treats the measurand as the difference between the unit under calibration (UUC) reading and the calibration pressure.
  • Quotient model - treats the measurand as a ratio (for sensitivities, constants, or coefficients).
• Uncertainty composition: Shows how to combine standard uncertainties (root-sum-square) from:
  • the UUC (device under test),
  • the reference standard (reference gauge),
  • calibration method and conditions (e.g., corrections for height, thermal transpiration, port differences).
• Uncertainty contributions: Details typical input quantities and influence terms (offsets, drift, calibration-certificate corrections, temperature effects, long‑term instability).
• Reporting requirements: Prescribes a uniform format for an uncertainty budget and content to include in a calibration certificate, including expanded uncertainty and coverage factor.
• Limitations and combination guidance: Notes that the two models cover most cases but may not apply to newly developed gauge types; combining models is possible but should be handled carefully by experts.

Practical applications

• Calibration laboratories use ISO 27893:2011 to:
  • compute and document measurement uncertainties consistently,
  • produce traceable calibration certificates for vacuum gauges,
  • provide uncertainty components that are usable in later calibrations or measurements.
• Metrologists and accreditation bodies use it to assess conformity of calibration methods and certificates.
• Manufacturers and quality managers rely on it to specify calibration tolerances, demonstrate traceability to the SI unit (pascal), and support product specifications where vacuum measurement accuracy is critical (research, semiconductor, coating, vacuum processing).

Related standards

• ISO/TS 3567 - Vacuum gauges - Calibration by direct comparison with a reference gauge (calibration procedure)
• ISO/IEC Guide 98-3 (GUM:1995) - Guide to the expression of uncertainty in measurement
• ISO/IEC Guide 99 (VIM) - International vocabulary of metrology

ISO 27893:2011 is essential for any organization needing reliable, traceable, and transferable uncertainty statements for vacuum gauge calibrations.