Overview
ISO/TR 22681:2019 is a Technical Report from ISO on hydraulic fluid power that explains the impact of the particle‑size shift introduced when calibration material SRM 2806a was replaced by SRM 2806b. The report clarifies the two acceptable particle‑size designations defined in ISO 11171:2016 - µm(c) (traceable to SRM 2806a) and µm(b) (traceable to SRM 2806b) - and describes how to interpret particle count and filter test (Beta Ratio) data consistently across the transition.
Key Topics
- Origins of the size shift: SRM 2806b used automated image analysis and tighter certification methods vs SRM 2806a, causing a measurable particle‑size shift.
- Conversion relationship: The report provides the conversion between notations:
µm(c) ≈ 0.898 × µm(b) (equivalently µm(b) ≈ 1.114 × µm(c)). This corresponds to an approximate 10.2% numerical difference in the 0–38 µm range.
- Impact on particle counts: For a given numerical size threshold, counts reported as µm(b) tend to be higher than the same threshold reported as µm(c); the magnitude depends on the sample’s particle size distribution.
- Effect on cleanliness codes: Using µm(b) values directly in ISO 4406 cleanliness coding (which requires µm(c)) can increase reported codes by about 1–2 code units in some examples, risking misinterpretation.
- Filter Beta Ratio implications: Direct comparison of Beta Ratios reported in µm(b) vs µm(c) is problematic; Beta Ratios typically appear worse when reported in µm(b) unless converted or consistently referenced.
- Traceability and reporting options: ISO 11171:2016 revision enables clear reporting of which basis (µm(b) or µm(c)) is used, allowing historical comparison and conversion where needed.
Applications
Who uses ISO/TR 22681:2019 and why:
- Contamination control engineers and maintenance teams - to interpret particle count data accurately and avoid unnecessary corrective actions.
- Filter manufacturers and test labs - to compare current performance data with historical records and avoid false rejections.
- Calibration and metrology laboratories - to ensure APC (automatic particle counter) calibrations are traceable and reported correctly.
- Standards writers and specifiers - to reference the correct particle‑size designation in procurement and quality documents.
Practical uses include harmonizing historic and new particle count datasets, converting size thresholds between µm(b) and µm(c), and ensuring consistent filter qualification and cleanliness reporting.
Related Standards
- ISO 11171:2016 (automatic particle counter calibration; µm(b)/µm(c) basis)
- ISO 4406 (cleanliness coding)
- ISO 16889 (filter testing, MTD/ UFTD dusts referenced)
- ISO 4402 (obsolete particle sizing calibration method; historical reference)
Keywords: ISO/TR 22681:2019, hydraulic fluid power, ISO 11171:2016, µm(b), µm(c), particle count, filter Beta Ratio, SRM 2806, APC calibration, contamination control.
Open preview (PDF)Hydraulic fluid power — Impact and use of ISO 11171:2016 µm(b) and µm(c) particle size designations on particle count and filter test data
