Experimental investigation of a light extinction based sensor assessing particle size and distribution in an oil system

Optical particle counters (OPCs) based on the light extinction measurement scheme are widely used in the industry for monitoring the level of wear debris in lubricating oil systems. In this work it is investigated how model-based size estimation and OPC output data can be correlated. Spherical metal coated 5–20 μm diameter particles were used in a laboratory oil system and monitored using an OPC. The raw OPC output data were extracted with the purpose of estimating the true particle size. Distribution parameters has been deducted from detected minima in output signals for each particle diameter using a half-normal fit centered at the detected kernel peak. Experiments with different sized particles showed that signal minima amplitude distributions differ between particle diameters thus, clearly showing the discrimination ability of the OPC. Furthermore, to obtain OPC based true size determination, the apparent absorption coefficient of the micrometer sized particles must be considered. Thus, reducing the maximum deviation between true and OPC determined diameter to 13%.