I have been asked for a description of the Pore Blockage method used in my used engine oil analysis: it is as follows:
Particle Counting (BS3406)
"The pore blockage method is a widely used method of obtaining an automatic particle count. In this method, a volume of fluid is passed through a mesh screen with a clearly defined pore size, commonly 10 microns. There are two instrument-types that use this method. One instrument measures the flow decay across the membrane as it becomes plugged while pressure is held constant, first with particles greater than 10 microns, and later by smaller particles as the larger particles plug the screen. The second measures the rise in differential pressure across the screen while the flow rate is held constant as it becomes plugged with particles. Both instruments are tied to a software algorithm, which turns the time-dependent flow decay or pressure rise into an ISO cleanliness rating according to ISO 4406:99.
While pore block particle counters do not suffer the same problems as optical particle counters with respect to false positive caused by air, water, dark fluid, etc., they do not have the same dynamic range as an optical particle counter, and because the particle size distribution is roughly estimated, are dependent on the accuracy of the algorithm to accurately report ISO fluid cleanliness codes according to ISO 4406:99. Nevertheless, they accurately report the aggregate concentration of particulates in the oil, and in certain situations, particularly dark fluids such as diesel engine oils and other heavily contaminated oils, pore block particle counting does offer advantages."
Particle Counting (BS3406)
"The pore blockage method is a widely used method of obtaining an automatic particle count. In this method, a volume of fluid is passed through a mesh screen with a clearly defined pore size, commonly 10 microns. There are two instrument-types that use this method. One instrument measures the flow decay across the membrane as it becomes plugged while pressure is held constant, first with particles greater than 10 microns, and later by smaller particles as the larger particles plug the screen. The second measures the rise in differential pressure across the screen while the flow rate is held constant as it becomes plugged with particles. Both instruments are tied to a software algorithm, which turns the time-dependent flow decay or pressure rise into an ISO cleanliness rating according to ISO 4406:99.
While pore block particle counters do not suffer the same problems as optical particle counters with respect to false positive caused by air, water, dark fluid, etc., they do not have the same dynamic range as an optical particle counter, and because the particle size distribution is roughly estimated, are dependent on the accuracy of the algorithm to accurately report ISO fluid cleanliness codes according to ISO 4406:99. Nevertheless, they accurately report the aggregate concentration of particulates in the oil, and in certain situations, particularly dark fluids such as diesel engine oils and other heavily contaminated oils, pore block particle counting does offer advantages."
