NAS-1638 Particle Count

Technique for detecting and categorizing particles in a used lube oil resulting from wear or contamination. Standard particle count is the NAS-1638 (National Aerospace Standard).  Only from the NAS-1638 can the ISO-4406 Solid Contamination Code be derived.  By the NAS test a laser passes through  a specified opening, as the fluid pass through, perpendicular to the laser source, particles and debris block out the laser source and by measuring the time of blockage determine the size of particles in the following size range:


5 - 15 m

15 - 25 m


25 - 50 m


50 - 100 m


> 100 m

Other non-direct particle count methods include: Flow Rate Decay, Electro Conductivity, Optical Density Equivalent, Magnetic Mass Equitant and others.  In the test, algorithms are calculated to approximate the particle quantities in each given size range.


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