TECHNICAL REFERENCE
The old particle counter calibration was based on only one dimension of an irregularly-shaped particle (the longest cord). Today, the particle counter calibration is based on equivalent spherical area of an irregularly-shaped particle. NIST provides calibration suspension, which is certified with X number of particles at a certain size. This is verified by NIST. The new way to list beta ratios includes a subscript (c) to indicate NIST certified test suspension and assures you of traceability and repeatability. Overall, you can have strong confidence in filter ratings resulting from tests per ISO 16889, as they are highly accurate. As always, keep in mind that beta ratings are laboratory measurements under steady flow conditions with artificial contaminants – the real proof of the performance is how clean the filter keeps
the fluids in the application. A good oil analysis program that checks the cleanliness of the oil periodically will verify that the proper filters are being used.
Test Dust Size Comparisons ACFTD calibrated size ( m) per ISO 4402 corresponds to a NIST-calibrated size [ m(c)] per ISO 11171
ACFTD 0.8 1
2
2.7 3
4.3 5
7
10 12 15 15.5 20 25 30 40 50
NIST 4
4.2 4.6 5
5.1 6
6.4 7.7 9.8 11.3 13.6 14 17.5 21.2 24.9 31.7 38.2
flow meter
In-Line Liquid Automatic Particle Counters (APC) are now required for proper testing. APC calibration follows ISO 11171 procedures ISO 11171 uses NIST (National Instistute of Standards & Technology) certified calibration fluid ISO 16889
Injection Reservoir
Down Stream
Online APC*
Test Filter
pump
Test Reservoir
Up Stream
Online APC*
* APC = Liquid Automatic Particle Counter
pump
flow meter
Injection Reservoir
Down Stream
ISO 4572 (Discontinued)
Bottle Sample
Test Filter
Either bottle samples
pump
or APC's were allowed. APC calibration followed ISO4402 ACFTD (Discontinued)
Up Stream
Test Reservoir
Bottle Sample
pump
Hydraulic Filters & Accessories • 31
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