ISO 25178-602:2025

Overview

ISO 25178-602:2025 specifies the design and metrological characteristics of non-contact areal surface texture instruments that use a confocal chromatic probe (axial chromatic aberration of white light). It is part of the ISO 25178 GPS (Geometrical Product Specification) series for areal surface texture measurement. The standard addresses the instrument architecture (optical pen, optoelectronic controller, fibre link), the information flow (spectral encoding and spectral decoding), and how areal data can also be used to extract profiles.

Keywords: ISO 25178-602, confocal chromatic probe, areal surface texture, non-contact profilometer, surface topography.

Key Topics and Requirements

• Instrument principle: Uses axial chromatic aberration of a chromatic objective combined with a white light source; focused wavelength encodes height information and a spectrometer decodes wavelength to height.
• Primary operations required:
  • Spectral encoding - stretching focus points by axial chromatic aberration (chromatic objective + broadband light).
  • Spectral decoding - identifying focused wavelength via a spectrometer and converting wavelength to height through calibration.
• Instrument components and terms:
  • Chromatic objective (optical pen), optoelectronic controller, light source pinhole and discrimination pinhole (often implemented via fibre optics), vertical range, stray light.
  • Typical spectral region often lies in the visible band (≈ 0.4 µm to 0.8 µm) as noted.
• Scanning modes: Point sensors (for profiles or areal scans), line sensors (line capture plus lateral motion), and use with rotary tables for roundness.
• Metrological characteristics: Designers and calibrators must account for the standard metrological characteristics defined in ISO 25178-600; Annex B lists sources of measurement error; Annex A explains confocal chromatic profilometry principles.
• Information flow and GPS compliance: The document includes an information flow diagram and aligns with the GPS matrix model.

Practical Applications and Users

• Applications:
  • Areal surface topography measurement for engineering surfaces (e.g., bearings, seals, precision machined parts).
  • Fast non-contact profiling where surface damage must be avoided.
  • Form and roundness measurements when integrated with rotary or CMM setups.
• Who uses it:
  • Metrology labs and calibration houses
  • Instrument manufacturers and optical designers
  • Quality assurance and inspection engineers in manufacturing
  • Standards committees and technical developers implementing GPS-compliant measurement solutions

Related Standards

• ISO 25178-600 - Metrological characteristics for areal topography measuring methods (normative reference)
• ISO 25178-2 - Areal surface texture parameters (parameter calculation)
• ISO 14638, ISO 8015, ISO 14253-1 - GPS framework and decision rules
• ISO 10934 - Terminology related to chromatic aberration (referenced for definitions)

This standard helps ensure confocal chromatic probe instruments are designed, calibrated, and documented consistently to produce reliable areal surface texture and profiling data.