On the basis of the image capture of the particle outlines, the particle is categorised by form of origin. The optical particle analysis procedure which we presented in detail in ÖlChecker Summer 2002, categorises individual particles and their formation mechanisms on the basis of particle form. No calibration of the counter is necessary during this evaluation on the basis of a defined pixel size. The size of the particles can be computed by means of the pixel count. A high-speed high resolution camera „shoots“ images of the particles. The particles are scattered in the cell and illuminated by laser light. During the investigation, the oil streams uniformly through a cell developed between two glass plates. Liquid particle counter with imaging techniques (OPA)įor counting particles in oils, OELCHECK uses a significantly improved method, optical particle analysis (OPA). In this method air bubbles and water, or silicon droplets can adulterate the result. A precondition for a correct determination is that the particles pass through the light beam in sequence, in order to avoid overlap in the measurement cell.
The devices are calibrated with a test liquid and pre-defined test pollution according to ISO 11171 and/or 11943. The larger the particle, the larger the voltage drop generated by the shaded area on the photocell.
A photocell receives the impinging light. Liquid particle counters with optical sensors (APC)Ī laser diode serves as a light source for particle counting. Most of the particle counting devices currently used in lubricant analysis function according to the principle of light attenuation or light blockade and use laser diodes as a light source. For this purpose, the first laboratory devices were developed during the 1970s.
Based on investigations with the microscope, additional qualitative statements may be made on the appearance, and in some cases, the origin of the detected particles.Īs an alternative to laborious manual particle counting with the microscope, particle counting was automated.
The observer can then either manually „count“ the particles extracted on the filter membrane under the microscope or assign them to a purity class by comparison with representative images. The oil is diluted with different solvents or also undiluted and filtered by means of pressure or vacuum admission flow through a membrane with pore sizes of 1.2 µm, 0.8 μm or 0.45 μm and a diameter of 47/50 mm. Even very dark and/or heavily contaminated fluids can be investigated in a targeted way with corresponding solvents on membranes arranged in cascade-like fashion with graduated pore sizes. Fibres and reflecting particles are very easy to recognise.
But despite the great effort: all particles appear under the microscope. In addition, it requires a trained eye and a great deal of experience on the part of the investigator, even if at an earlier stage, when simple counting devices (totalisers) were deployed, microscopic particle counting represented an almost Herculean task for the laboratory assistant. Manual microscopic particle counting was and is extremely time consuming and strenuous. But the new device opens perspectives achieved by no other particle counting equipment, even if at the start of the particle counting there really was a conventional microscope. In order to be on the safe side in cases of doubt and to exclude these influences, we have installed a special OLYMPUS testing device in the OELCHECK laboratory: The automated microscopic particle counter with integrated image analysis software!ĭo we go back to the good old microscope for counting particles in the laboratory? At first sight, it seems so. air bubbles, droplets of water or roughly dispersed components inherent to the oil can influence counting in unfavourable situations. A disadvantage of this technology lies in the fact that, e.g. Most of these function according to the principle of light attenuation or blocking. For determining solid impurities, the deployment of automatic particle counters represents state-of-the-art technology. The first number relates to particles >4 µm, the middle number to particles >6 µm and the number on the right to large particles >14 µm. The purity class according to ISO 4406/1999 is indicated as a composite number, such as 21/18/13. The level of contamination of an oil due to solid particles is reflected by its purity class. 50-70% of all faults and failures in hydraulic and lubricant installations can be attributed to operating fluid contaminated by solid particles or by fluid or gaseous foreign substances. Particularly for hydraulic systems, oil impurities represent one of the most significant risk factors. Clean is not pure! And even oil which looks pure at first sight can still be contaminated by the smallest particles.