PARTICLE COUNT: ISO 4406 (view limits)
Particle counters report particulate levels in a fluid. Results are given in the number of particles per ml. in six size ranges. While a particle count does not identify what the particulate is, as a rule it provides a general idea of how “clean” the lubricant is.
Cleanliness requirements vary depending on the components and pressures present in a system. A hydraulic system with servo valves needs to have a much lower particle count than a gear box, for example. Many equipment manufacturers provide acceptable particle count levels for their systems. We will also be glad to help you set alarm levels based on the components in your systems.
Laser Particle Counter
The laser particle counter is our instrument of choice in most situations. As the laser beam strikes the particle, light scatters and hits the photocell. The change in voltage across the photocell is directly related to the size of the particle. In the laser-based instrument, one looks at an increased signal against what should be a zero background (in theory). Laser optical particle counters are generally considered to be more accurate and sensitive than white light instruments.
Pore Blockage Particle Counter
When water is present or for diesel engine samples the pore blockage particle counter is used. These instruments measure flow decay and/or pressure drop across a calibrated screen – usually 10 micron pore size. As the screen becomes blocked with particles greater than 10 microns, and later by smaller particles as the larger particles plug the screen the flow of oil decreases across the screen and the differential pressure across the screen increases. These instruments are tied to a software algorithm, which turns the time-dependent flow decay or pressure rise into an ISO cleanliness rating according to ISO 4406:99.
While pore block particle counters are not affected by air, water, dark fluid, etc., they do not have the same dynamic range as an optical particle counter. Since the particle size distribution is roughly estimated, they rely on the accuracy of the algorithm to accurately report ISO fluid cleanliness codes according to ISO 4406:99. Still, they do offer repeatability and the results can be trended. Also, in certain situations, particularly dark fluids such as diesel engine oils, wet samples and other heavily contaminated oils, pore block particle counting does offer advantages.
See chart on following page for the ISO 4406 Standard Particle Count Chart
ISO 4406 Standards for Particle Counting
Application Note 6 - ISO 4406 Standards for Particle Counting
Number of Particles per ml
Up to & Including
The ISO 4406 cleanliness code specifies three size ranges. The scale number refers to the number of particles per 1 ml if fluid in each size range. The scale numbers are reported with a backslash between them in this order: >4 / >6 / >14 (microns).