ISO 4407:2025

Hydraulic fluid power — Fluid contamination — Determination of particulate contamination by the counting method using an optical microscope

Scope

This document specifies acceptable methods for determining the level of particulate contamination in a known volume of fluid used in power systems by counting the number of particles captured on the surface of a filter membrane using an optical microscope. It includes accepted methods of particle counting utilising image analysis software or manual counting.
The aim of this document is to regulate a uniform, non-subjective filter membrane method of particle counting that will ensure that the classification standard result is achieved by analysing, where feasible, the entire effective filtration area (EFA) of the filter membrane.
The resolution and accuracy of the results will be dependent upon the optical system used, whether image capture analysis software is used, and when opting for the manual counting method, the capabilities of the operator.
All fluids that can be successfully vacuumed through the appropriate pore sized filter membrane will be able to use the following 2 methods of membrane filter analysis:
—     Automated counting (see Annex A): automated detection, size classification and counting of particles on a membrane filter by using an optical microscope and image analysing software.
—     Manual counting (see Annex B): manual detection, size classification and counting of particles on a membrane filter using an optical microscope.