Overview
ISO 11943:2021 - "Hydraulic fluid power - Online automatic particle-counting systems for liquids - Methods of calibration and validation" - defines procedures to calibrate and validate online automatic particle counters (APCs) and the hydraulic systems that supply them. The standard covers preparation and validation of secondary calibration suspensions, online secondary calibration of APCs, matching two or more online counters, and validation of online particle-counting systems with or without online dilution (for example, during the ISO 16889 multi-pass filter test).
Key topics and technical requirements
- Scope of calibration and validation
- Validation of equipment used to prepare secondary calibration suspensions.
- Online secondary calibration of APCs and matching multiple APCs so they report equivalent counts at given sizes.
- Validation of complete online counting systems, including dilution circuits, used for filtration-efficiency testing.
- Measurement accuracy and test conditions
- The standard specifies accuracy limits for flow, temperature, viscosity and timing instrumentation and requires control of test conditions to ensure repeatability.
- Particle sizing is reported in µm(c) in accordance with ISO 11171.
- Test materials and procedures
- Use of ISO medium test dust (ISO MTD, per ISO 12103-1) mixed into test fluid and dispersed before measurement.
- Typical target dust concentration and clean-up criteria are given to achieve repeatable particle distributions.
- Statistical validation
- Online system validation relies on repeated particle counts over time and statistical analysis (means and standard deviations) against acceptable limits derived from inter-laboratory studies (see Annex C).
- Guidance material
- Informative annexes provide typical online calibration system design, hydraulic circuit guidance for multi-pass rigs, and inter-laboratory study results.
Practical applications and users
ISO 11943:2021 is used by:
- Hydraulic system and component manufacturers (filters, pumps, valves) conducting filtration-efficiency tests.
- Test laboratories and OEM quality teams performing online contamination monitoring and APC calibration.
- Instrumentation and sensor vendors validating APCs and dilution systems for online deployment.
- Maintenance and contamination-control engineers implementing in-line particle monitoring for condition-based maintenance.
Practical benefits include improved confidence in online particle counts, consistent filter test results (ISO 16889), and the ability to match multiple APCs for comparative tests.
Related standards
- ISO 11171 - Calibration of automatic particle counters for liquids
- ISO 16889 - Multi-pass method for evaluating filter performance
- ISO 12103-1 - Test dust (Arizona/ISO MTD)
- ISO 4021 - Fluid sampling from operating systems
- ISO 5598 - Fluid power vocabulary
Keywords: ISO 11943:2021, online automatic particle-counting systems, APC calibration, validation, hydraulic fluid power, secondary calibration suspensions, online dilution, multi-pass filter test.