1、Designation: D6786 15Standard Test Method forParticle Count in Mineral Insulating Oil Using AutomaticOptical Particle Counters1This standard is issued under the fixed designation D6786; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of particleconcentration and particle size distribution in mi
3、neral insulat-ing oil. It is suitable for testing oils having a viscosity of 6 to20 mm2/s at 40C. The test method is specific to liquidautomatic particle analyzers that use the light extinctionprinciple.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement ar
4、e included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations p
5、rior to use.2. Referenced Documents2.1 ASTM Standards:2D923 Practices for Sampling Electrical Insulating Liquids2.2 ISO Standards:4406:1999 Hydraulic Fluid PowerFluidsMethod forCoding the Level of Contamination by Solid Particles311171:2010 Hydraulic Fluid PowerCalibration of Auto-matic Particle Cou
6、nters for Liquids33. Terminology3.1 Definitions:3.1.1 coincidencethe presence of more than one particlein the sensing zone of a particle analyzer at the same time,causing mis-sizing and mis-counting of the particle present.The coincidence limit of the counter is determined by themaximum acceptable c
7、oncentration of particles in the sensingzone and is supplied by the instrument manufacturer.3.1.2 concentration limita direct function of coincidenceand electronic saturation. The concentration limit of the systemis determined by the maximum acceptable concentration ofparticles in the given sample a
8、nd is supplied by the instrumentmanufacturer.3.1.3 electronic saturation levelparticle concentration atwhich the electronic circuitry of the analyzer ceases to functionproperly due to excessive counting rates.3.1.4 light extinctionthe reduction in intensity of a lightbeam passing through the sensing
9、 zone of a particle analyzer,caused by the absorption and/or scattering of the light byparticles. Synonyms: light obscuration, light interruption, lightblockage.4. Summary of Test Method4.1 Samples are taken in particle-clean bottles that aresuitable for particle analysis. The sample bottle is agita
10、ted toredistribute particles in the oil, then the oil is placed in anautomatic particle counter, where the number of particles andtheir size distribution are determined by the light extinctionprinciple.4.2 As particles pass through the sensing zone of theinstrument, the quantity of light reaching th
11、e detector isobscured. This signal is translated to an equivalent projectedarea diameter based on calibration with a NIST-traceable fluid(ISO Medium Test Dust suspension).5. Significance and Use5.1 Particles in insulating oil can have a detrimental effecton the dielectric properties of the fluid, de
12、pending on the size,concentration, and nature of the particles. The source of theseparticles can be external contaminants, oil degradation by-products, or internal materials such as metals, carbon, orcellulose fibers.5.2 Particle counts provide a general degree of contamina-tion level and may be use
13、ful in assessing the condition ofspecific types of electrical equipment. Particle counts can alsobe used to determine filtering effectiveness when processingoil.1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gases and is the direct responsibilit
14、y of Subcom-mittee D27.07 on Physical Test.Current edition approved Oct. 1, 2015. Published October 2015. Originallyapproved in 2002. Last previous edition approved in 2008 as D678608. DOI:10.1520/D6786-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer
15、Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International
16、, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.3 If more specific knowledge of the nature of the particlesis needed, other tests such as metals analysis or fiber identifi-cation and counting must be performed.6. Interferences6.1 Dirty environmental conditions
17、 and poor handling tech-niques can easily contaminate the sample and/or test specimen.Care must be taken to ensure test results are not biased byintroduced particles.6.2 Air bubbles in the oil may be counted as particles givingfalse positive readings. Mixing or agitating the sample intro-duces bubbl
18、es into the oil. These are dissipated using vacuumor ultrasonic bath.6.3 Suspended or free water in the oil will interfere withparticle counts.6.4 Excessive concentrations of particles in the oil willcause coincidence and/or electronic saturation errors. Limitsare determined by ISO 11171 and are gen
19、erally supplied by theinstrument manufacturer. These errors may be avoided bydiluting the sample with particle-clean dilution oil or particle-clean solvent.6.5 Odd-shaped particles and fibers may be improperlyanalyzed, depending on their orientation as they pass throughthe sensing zone of the instru
20、ment.7. Apparatus7.1 Automatic Particle Counter, liquid optical particle coun-ter based on the light extinction principle. The instrument shallbe capable of recording the size and number of particles as theypass across the detector. The particle counter shall include abottle sampling apparatus that
21、automatically delivers a prede-termined volume of specimen at a controlled flow rate to thesensing zone of the analyzer.7.2 Mechanical Shaker, paint shaker, table shaker, or othermechanical device to vigorously agitate sample bottles.7.3 Ultrasonic Bath, with a power density of 3000 to 10 000W per m
22、2of bottom area.8. Materials8.1 Particle-clean Bottles, recommended sample containersare 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-mLcapacity. The bottles shall meet the cle
23、anliness criteria ofcontributing less than 1 % of the total particles expected in thecleanest sample.8.2 Particle-clean Solvent, petroleum spirits, hexane,kerosene, or other suitable solvent, filtered through a 0.45 mmembrane filter.8.3 Calibration Fluid, suspension of ISO Medium Test Dustin oil or
24、hydraulic fluid, either a primary sample obtaineddirectly from NIST4(SRM 2806) or a secondary sampleprepared in accordance to ISO 11171 and traceable to NIST.8.4 Dilution Oil, insulating oil that has been filtered tocontain fewer than 1 % of the total particles expected in thecleanest sample.9. Samp
25、ling9.1 Proper sampling is crucial to particulate analysis. Obtaina sample of the liquid to be tested in accordance with PracticeD923.10. Calibration10.1 Calibration of the instrument shall be with a NIST-traceable calibration fluid in accordance with ISO 11171.10.2 Calibrate the instrument annually
26、, unless experiencejustifies longer or shorter intervals.10.3 Interim calibration checks should be made regularly byusing a particle count standard fluid prepared using theprocedures of ISO 11171. If the average number of counts is atleast 100, the check values should be within 20 % of thestandard v
27、alues.11. Procedure11.1 If necessary, wipe the outside of the sample bottle witha clean lint-free towel.11.2 If other tests are to be run on the same sample, shakethe sample bottle as described in 11.3 and transfer a specimenfor particle count to another particle-clean bottle. Do thisbefore running
28、any other tests in order to avoid contamination.11.3 Ultrasonically disperse for 30 to 40 s then agitate thesample bottle vigorously for 30-60 s to redistribute particles,the length of time depending on the effectiveness of the methodof agitation. Preferably use a mechanical shaker. Do not use amagn
29、etic stir bar or any other device that comes in contact withthe oil.11.4 Apply vacuum to the bottle, or use the ultrasonic bath,or both, until bubbles dissipate.11.5 Immediately analyze the sample with the automaticparticle counter according to the manufacturers operatinginstructions. Usually the an
30、alyzer is flushed with a specimen ofthe oil prior to testing. After the initial flush, 2-3 runs on eachsample are recommended.11.6 When particle count runs are finished, flush the instru-ment with particle-clean solvent or particle-clean oil in accor-dance with the instrument manufacturers recommend
31、ations.12. Report12.1 Report the average of the particle count runs as thecumulative number of particles per mL 4, 6, 10, 14, 21,38, and 70 m (c). The “(c)” after the size indicates that theparticle counter was calibrated using ISO 11171. These particlesizes correspond approximately to 2, 5, 10, 15,
32、 25, 50,and 100 m for particle counters that were calibrated with theold ISO 4402 calibration standard. If only one particle countrun is analyzed, report the results of the single run.12.2 Optionally, also report the ISO solid contaminant codecorresponding to the number of particles per mL 4, 6, and
33、 14m (c), as prescribed in ISO 4406:1999.4Available from National Institute of Standards and Technology, 100 BureauDrive, Gaithersburg, MD 20899.D6786 15213. Precision and Bias13.1 A round robin is planned to determine the precisionand bias of this test method.14. Keywords14.1 optical particle count
34、er; particle count; particulatecontaminationASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and
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