C
ourtesy of Pamas
To display particle counts in oil and fuel samples and even water-based hydraulic fluids, in a simplified and uniform way, results are often reported in cleanliness classes according to a specific reporting standard. In the following article we discuss the most common and important international standard the ISO 4406 triple code.
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ISO 4406:2017 Particle sizes: The cleanliness classes as per ISO 4406 are determined by the cumulative counts in the size bands >4µm(c), >6µm(c) and >14µm(c). To comply with the ISO-standardization process, the particle sizes have been redefined. Particle sizes are now displayed as µm(c). The additional (c) indicates that the particle counter has been calibrated according to ISO 11171. This enables the old and new measurements to be easily identified and differentiated. 1µm as per ISO 4402 equals approximately to 4µm(c) as per ISO 11171. Calibration: The ISO 4406 reporting standard is based on the calibration standard ISO 11171. The calibration media used is called ISO MTD (ISO Medium Test Dust) and it was introduced after the end of production of ACFTD (Air Cleaner Fine Test Dust) which had been previously used to calibrate particle counters according to ISO 4402.
Perhaps an example would better demonstrate how this triple code classification works. Imagine your liquid particle counter measured 300 000 particles per 100 ml for particles larger than 4 um, 50 000 particles larger than 6 um and only 700 particles larger than 14 um. From the table for 4 um the class no would be 19 ( result is between 250 000 and 500 000). For 6 um the result is between 32 000 and 64 000 which is class 16 and for 14 um the results falls between 500 and a 1000 which is class 10. So the ISO code would be 19/16/10 in this example. The trick, if you can it that, is to simply to keep in mind what the sample volume is, your instrument report the particle count for. In the case of a Pamas SBSS the result in the software is normally set to 100 ml, while for the portable S40 10 ml is a popular sample size and if multiple samples are measured the average would be reported to 100 ml as well.
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