Cleanliness Code Of A Lubricating Oil

ISO 4406:1999 Scale Number Table

Number of particles per milliliter

 

Scale number

More than Up to and including
2 500 000 >28
1 300 000 2 500 000 28
640 000 1 300 000 27
320 000 640 000 26
160 000 320 000 25
80 000 160 000 24
40 000 80 000 23
20 000 40 000 22
10 000 20 000 21
5 000 10 000 20
2 500 5 000 19
1 300 2 500 18
640 1 300 17
320 640 16
160 320 15
80 160 14
40 80 13
20 40 12
10 20 11
5 10 10
2.5 5 9
1.3 2.5 8
0.64 1.3 7
0.32 0.64 6
0.16 0.32 5
0.08 0.16 4
0.04 0.08 3
0.02 0.04 2
0.01 0.02 1
0 0.01 0

NOTES: For automatic particle counter analysis, the contaminant code is determined by allocating a first scale number to the total number of particles equal to or larger than 4 μm, allocating a second scale number to the total number of particles equal to or larger than 6 μm and allocating a third scale number to the total number of particles equal to or larger than 14 μm, and then writing these three numbers one after another separated by oblique strokes (slashes). For an example, see 22/18/13 in the table above. For analysis by microscope, use a "—" in place of the first scale number and allocate the second and third numbers based on the counts at 5 μm and 15 μm, respectively.
Reproducibility below scale number 8 is affected by the actual number of particles counted in the fluid sample. Raw counts should be more than 20 particles. If this is not possible, then the scale number for that size range shall be labelled with the symbol ≥.
EXAMPLE: A code of 14/12/≥ 7 signifies that there are more than 80 and up to and including 160 particles equal to or larger than 4 μm per millilitre and more than 20 and up to and including 40 particles equal to or larger than 6 μm per millilitre. The third part of the code, ≥ 7, indicates that there are more than 0.64 and up to and including 1.3 particles equal to or larger than 14 μm per millilitre, but less than 20 particles were counted, which lowers statistical confidence. Because of this lower confidence, the 14 μm part of the code could actually be higher than 7, indicating a particle count more than 1.3 particles per millilitre.