ASTM D6786 Test Method for Particle Count in Mineral Insulating Oil
ASTM D6786 Standard Test Method for Particle Count in Mineral Insulating Oil Using Automatic Optical Particle Counters
7. Apparatus
7.1 Automatic Particle Counter, liquid optical particle counter based on the light extinction principle. The instrument shall be capable of recording the size and number of particles as they pass across the detector. The particle counter shall include a bottle sampling apparatus that automatically delivers a predetermined volume of specimen at a controlled flow rate to the sensing zone of the analyzer.
7.2 Mechanical Shaker, paint shaker, table shaker, or other mechanical device to vigorously agitate sample bottles.
8. Materials
8.1 Particle-clean Bottles, recommended sample containers are cylindrical bottles made of polypropylene, polystyrene, PET, or glass with flat bottoms, fitted with a suitable non-shedding threaded cap. Bottles should be at least 100-mL capacity. The bottles shall meet the cleanliness criteria of contributing less than 1 % of the total particles expected in the cleanest sample.
8.2 Particle-clean Solvent, petroleum spirits, hexane, kerosene, or other suitable solvent, filtered through a 0.45 µm membrane filter.
8.3 Calibration Fluid, suspension of ISO Medium Test Dust in oil or hydraulic fluid, either a primary sample obtained directly from NIST4 (SRM 2806) or a secondary sample prepared in accordance to ISO 11171 and traceable to NIST.
8.4 Dilution Oil, insulating oil that has been filtered to contain fewer than 1 % of the total particles expected in the cleanest sample.
9. Sampling
9.1 Refer to Practice D923 for precautions for sampling from energized electrical equipment.
9.2 Proper sampling is crucial to particulate analysis. The following guidelines are offered to ensure representative sampling and to preserve sample integrity:
9.2.1 Wipe the sample port outlet with a clean lint-free towel. Open the sample valve and flush about 3 times the flow path volume of oil into a container.
9.2.2 While flushing, uncap the sample bottle and retain the cap in one hand and the bottle in the other. Without adjusting the valve or disturbing sample flow, fill the bottle to about 80-95 % capacity. Do not completely fill the bottle since the headspace will be needed for sample agitation.
9.2.3 Cap the sample bottle, then close the sample valve.
