Particle count
the number of particles present greater than a particular micron size per unit volume of fluid. Selected methods of particle counting are:
| automated optical | where particles are directly sized and counted using the dispersion or blockage of light created by a solid particle passing between a light source and a sensor |
| Image analysis | where stationary particles are directly sized and counted under the microscope by manual or automated systems; |
| Electrical resistance | which measures the volume of a particle as it passes through an orifice in an electrically conductive liquid; |
| Flow decay | where count and size data is extrapolated from a standard equation applied to the rate at which flow decreases through a screen as particles block it. |
