parTicle counting

Particle Count analysis, as the name implies, counts the number of particles in a given size range in a given volume of sample. We use three different particle counting methods: Laser Light Scattering, Flow Degradation Curve Analysis, and Microscopic Examination/Count. All three of these methods are capable of counting the number of particles on a given size range. The number of particles and size distributions are then used to determine the Class of Cleanliness. Three different classifications are used throughout the industry: SAE 749D, NAS 1638, or ISO 4406. Each of these classification types has different size groupings and ratings.

Laser Light Scattering
An oscillating laser beam scans a known volume of sample over a given period of time. By measuring the intensity of scattered light and the intensity of incident light in a known period of time, a particle count by micron size can be determined.

Advantages

  • The instrument is sensitive to particles down to approximately 4 microns.
  • Results are easily converted to any of the three standard reporting classifications.

Disadvantages

  • The instrument reads even minute air bubbles as particles.
  • The instrument is sensitive to changes in the oils color.
  • Large particles may settle out before being counted in low viscosity fluids.
  • It may be time consuming when analyzing very "dirty" oil.


Flow Degradation Curve Analysis
This instrument uses a calibrated sensor screen, through which contaminated fluids are passed under pressure. This produces a distinctive flow decay curve, which is then analyzed by a proprietary computer formula, and particle count results are produced. This instrument and formula were developed by Diagnetics, Inc. of Tulsa, OK.

Advantages

  • Results are not affected by air bubbles, water, or color.
  • Results are comparable with other accepted methods.
  • Tests are relatively quick and simple.

Disadvantages

  • Equipment Cost.
  • Compressed air-supply required.
  • Frequent sensor screen replacement.


Microscopic Count
This method employs the use of a gridded filter through which 100 ml of fluid, diluted with solvent, is passed. Particles greater than 1 micron are trapped on the patch, which is then examined under a microscope. Each patch contains 100 grids. The accepted method of counting and sizing particles is to first examine the patch to make sure particles are evenly distributed across all the grids. Then select ten representative grids and manually count the particles in each size range. The ten results are averaged and multiplied by 100 to give results in particles/100 ml according to their size range.

Advantages

  • Careful patch examination will probably produce the most accurate results of these three methods.
  • Results are unaffected by air bubbles, water, or fluid color.

Disadvantages

  • Very time consuming and tedious.