ISO 11171:2022

Overview

ISO 11171:2022 - Hydraulic fluid power - Calibration of automatic particle counters for liquids - defines standardized procedures to calibrate automatic particle counters (APCs) used to size and count particulates in hydraulic fluids, fuels and lubricating oils. The standard establishes primary and secondary particle‑sizing calibration methods, performance limits and verification steps to ensure repeatable, traceable particle measurements for contamination control in fluid power systems.

Key topics and technical requirements

• Primary calibration using NIST SRM 2806x suspensions for particle sizes ≤ 30 µm(c) and polystyrene latex spheres for larger sizes. (Note: SRM 2806b is explicitly not applicable.)
• Secondary calibration using suspensions verified against a primary‑calibrated APC (e.g., NIST RM 8631x, ISO MTD or ISO 12103-1 test dust).
• Performance metrics and operating limits: resolution, counting accuracy, coefficient of variation (CV) for sample volume and flow rate, threshold noise level, coincidence error limit, and working flow rate.
• Verification procedures and annexes covering: preliminary APC checks (Annex A), coincidence error (Annex B), flow rate limits (Annex C), resolution determination (Annex D), particle‑counting accuracy (Annex E), preparation/verification of secondary suspensions (Annex F), dilution methods (Annex G) and particle size distribution verification (Annex H).
• Materials & diluents: requirements for polystyrene latex spheres (aqueous, CV < 5 %, certificates of analysis), clean diluent conductivity ((2 500 ± 1 000) pS/m), aerosol OT preparation for >30 µm(c) work, and handling/drying guidance for test dusts and reagents.

Practical applications and users

ISO 11171:2022 is essential for:

• Calibration laboratories and metrology services performing APC calibrations to ensure traceability to NIST standards.
• APC manufacturers validating sensor resolution, threshold noise and counting performance.
• Maintenance and contamination control engineers in hydraulics, aerospace (aviation fuel), diesel fuel, engine oil and other petroleum‑based fluid industries.
• Filter test facilities and OEMs requiring reliable particle counts for component qualification and condition monitoring.

Using ISO 11171 helps organizations produce consistent, comparable particle concentration and size‑distribution data for cleanliness specifications, troubleshooting, filter evaluation and preventive maintenance programs.

Related standards

Normative references include ISO 3722, ISO 4787, ISO 5598, ISO 12103‑1 (Arizona test dust) and ISO 16889 (multi‑pass filter test). These documents complement ISO 11171 for sampling, vocabulary, test contaminants and filtration performance.