Overview
EN ISO 12181-2:2011 - "Geometrical product specifications (GPS) - Roundness - Part 2: Specification operators" (ISO 12181-2:2011) is a GPS standard adopted by CEN that defines the complete, ordered set of unambiguous specification operations used to specify roundness for integral features (complete roundness profiles of the type circle). It specifies the transmission band, the required filtering behavior and metrological constraints needed to make roundness specifications unique and repeatable.
Key topics and technical requirements
- Scope: Applies only to integral features and complete roundness profiles (features of the type circle).
- Complete specification operator: A full ordered set of specification operations (per ISO 17450-2) that must be stated explicitly to avoid ambiguity.
- Filters / Transmission band:
- Uses phase‑correct filters (per ISO 11562).
- Longwave‑pass filter: transmits from 1 UPR (undulations per revolution) and attenuates around the cut‑off frequency; attenuation is defined mathematically in the standard.
- Shortwave‑pass filter: transmits undulations shorter than its cut‑off; when used it must be specified together with a longwave‑pass filter to define a clear UPR band.
- Limiting UPR and metrological minima (selected values from the standard):
- Cut‑off 15 UPR → minimum 105 samples; minimum d:r = 5
- Cut‑off 50 UPR → minimum 350 samples; minimum d:r = 15
- Cut‑off 150 UPR → minimum 1 050 samples; minimum d:r = 50
- Cut‑off 500 UPR → minimum 3 500 samples; minimum d:r = 150
- Cut‑off 1 500 UPR → minimum 10 500 samples; minimum d:r = 500
- Example: a transmission band of 50–500 UPR requires 3 500 samples and d:r ≥ 150.
- Stylus/probing considerations: The standard does not impose defaults for filter UPR, probe tip radius or method of association (reference circle) - these must be explicitly stated in a specification or the specification is ambiguous.
- Measurement notes: It advises a measuring force of zero N for the specification operator (to eliminate elastic deformation effects) and highlights aliasing/harmonic content issues (see Annex A).
Applications and users
- Who uses it: Metrology labs, quality engineers, mechanical designers, manufacturing engineers, inspection system vendors and calibration laboratories.
- Practical uses:
- Writing unambiguous roundness tolerances on drawings and specifications.
- Setting measurement procedures and software for roundness instruments.
- Selecting probe tip geometry and sampling strategies to meet metrological requirements.
- Ensuring comparability of roundness results across suppliers and inspection systems.
Related standards
- ISO 12181-1 (vocabulary & parameters of roundness)
- ISO 11562 (phase‑correct filters for profile filtering)
- ISO 17450-2 (GPS specification operators and uncertainties)
- ISO 14253-1 (decision rules for proving conformance)
Keywords: roundness, GPS, ISO 12181-2, specification operators, transmission band, UPR, phase‑correct filter, stylus tip radius, roundness measurement.
