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Particle Count Test
 The ISO Code is a system for representing particle concentrations in oil. The test
is commonly referred to as the Particle Count. Without the use of the ISO Code, a confusing series of numbers would have to be examined to determine how clean an oil is.
In oil laboratories, automatic particle counters determine the ISO code. Shown
here is a particle count report for a hydraulic oil.
The number of particles are counted in seven different size ranges (see the
sample Particle Count test results below). The left column shows the size in microns. The right column is the number of particles counted in the sample that are larger than each
micron size. In the sample below, the number of particles found above 5 microns in size was 244.
The ISO Code in this example is 15/12. These two numbers (15 and 12) identify a range of particles
counted in the size above 5 microns and 15 microns, respectively. The higher the ISO Code, the dirtier
the oil. However, different oils can have different levels of "clean" and "dirty." The chart below shows the ranges for four types of oil:
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12/9
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14/11
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16/13
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18/15
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20/17
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22/19
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24/21
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26/23
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Hydraulic Fluids
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v. clean clean dirty
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Gear Oils
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v. clean clean v. dirty
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Engine Lubes
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v. clean clean dirty
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Turbine Oils
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v. clean clean dirty
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Part. >10µ/mL:
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68
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Grav.:
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0.5 mg/L
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ISO:
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15/12
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SAE:
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4
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NAS (>5µ):
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7
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Size Distribution
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(Hydraulic)
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Screen Size 10
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>SIZE
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COUNT
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>2µ =
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661
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>5µ =
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244
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>10µ =
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68
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>15µ =
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26
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>25µ =
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6
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>50µ =
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1
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>100µ =
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0
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