1、Designation: D 6786 02Standard Test Method forParticle Count in Mineral Insulating Oil Using AutomaticOptical Particle Counters1This standard is issued under the fixed designation D 6786; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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
3、 mineral insulat-ing oil. It is suitable for testing oils having a viscosity of 6 to20 cSt at 40C. The test method is specific to liquid automaticparticle analyzers that use the light extinction principle.1.2 This standard does not purport to address all of thesafety concerns, if any, associated wit
4、h 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 prior to use.2. Referenced Documents2.1 ASTM Standards:D 923 Practices for Sampling Electrical Insulating Liquids22.2 ISO S
5、tandards:4406:1999 Hydraulic Fluid PowerFluidsMethod forCoding the Level of Contamination by Solid Particles311171:1999 Hydraulic Fluid PowerCalibration of Auto-matic Particle Counters for Liquids33. Terminology3.1 Definitions:3.1.1 coincidencethe presence of more than one particlein the sensing zon
6、e 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 concentration of particles in the sensingzone and is supplied by the instrument manufacturer.3.1.2 concentration limita di
7、rect function of coincidenceand electronic saturation. The concentration limit of the systemis determined by the maximum acceptable concentration ofparticles in the given sample and is supplied by the instrumentmanufacturer.3.1.3 electronic saturation levelparticle concentration atwhich the electron
8、ic 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 zone of a particle analyzer,caused by the absorption and/or scattering of the light byparticles. Synonyms: light obscura
9、tion, light interruption, lightblockage.4. Summary of Test Method4.1 Samples are taken in particle-clean bottles that arededicated to particle analysis. The sample bottle is agitated toredistribute particles in the oil, then immediately placed in anautomatic particle counter, where the number of par
10、ticles 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 the detector isobscured. This signal is translated to an equivalent projectedarea diameter based on calibration with a NIS
11、T-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, depending on the size,concentration, and nature of the particles. The source of theseparticles can be external contaminant
12、s, 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 useful in accessing the condition ofspecific types of electrical equipment. Particle counts can alsobe used to determine fi
13、ltering effectiveness when processingoil.5.3 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 and poor handling tech-niques can easily con
14、taminate the sample and/or test specimen.Care must be taken to ensure test results are not biased byintroduced particles.1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gases and is the direct responsibility of Subcom-mittee D27.07 on Physical Te
15、sts.Current edition approved April 10, 2002. Published June 2002.2Annual Book of ASTM Standards, Vol 10.03.3Available from American National Standards Institute, 11 West 42nd Street,New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959
16、, United States.6.2 Air bubbles in the oil may be counted as particles givingfalse positive readings. Mixing or agitating the sample intro-duces bubbles into the oil, but these readily dissipate andgenerally do not interfere with insulating oil particle counts.6.3 Suspended or free water in the oil
17、will generally becounted as particles. Normally, free water concentrationsbelow 10 ppm will not interfere.6.4 Excessive concentrations of particles in the oil willcause coincidence and/or electronic saturation errors. Limitsare determined by ISO 11171 and are generally supplied by theinstrument manu
18、facturer. 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 instrument.7. Apparatus7.1 Automatic Partic
19、le Counter, liquid optical particlecounter based on the light extinction principle. The instrumentshall be capable of recording the size and number of particlesas they pass across the detector. The particle counter shallinclude a bottle sampling apparatus that automatically deliversa predetermined v
20、olume of specimen at a controlled flow rateto the sensing zone of the analyzer.7.2 Mechanical Shaker, paint shaker, table shaker, or othermechanical device to vigorously agitate sample bottles.8. Materials8.1 Particle-clean Bottles, recommended sample containersare cylindrical bottles made of polypr
21、opylene, 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 cleanliness criteria ofcontributing less than 1 % of the total particles expected in thecleanest sample.8.2 Particle-clean Sol
22、vent, petroleum spirits, hexane, kero-sene, or other suitable solvent, filtered through a 0.45 mmembrane filter.8.3 Calibration Fluid, suspension of ISO Medium Test Dustin oil or hydraulic fluid, either a primary sample obtaineddirectly from NIST4(SRM 2806) or a secondary sampleprepared in accordanc
23、e 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. Sampling9.1 Refer to Practice D 923 for precautions for samplingfrom energized electrical equipment.9.2 Proper sampling is cr
24、ucial to particulate analysis. Thefollowing guidelines are offered to ensure representative sam-pling and to preserve sample integrity:9.2.1 Wipe the sample port outlet with a clean lint-freetowel. Open the sample valve and flush about 3 times the flowpath volume of oil into a container.9.2.2 While
25、flushing, uncap the sample bottle and retain thecap in one hand and the bottle in the other. Without adjustingthe valve or disturbing sample flow, fill the bottle to about 80 %capacity. Do not completely fill the bottle since the headspacewill be needed for sample agitation.9.2.3 Cap the sample bott
26、le, then close the sample valve.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, unless experiencejustifies longer or shorter intervals.10.3 Interim calibration checks should be mad
27、e regularly byusing a particle count standard fluid prepared using theprocedures of ISO 11171. The check values should be within10 % of the standard values.11. Procedure11.1 If necessary, wipe the outside of the sample bottle witha clean lint-free towel.11.2 Agitate the sample bottle vigorously for
28、2-5 min toredistribute particles, the length of time depending on theeffectiveness of the method of agitation. Use hand shaking ora mechanical shaker. Do not use a magnetic stir bar or anyother device that comes in contact with the oil. Do not use anultrasonic bath as this may break up the large par
29、ticles.11.3 Allow a few seconds for gas bubbles to escape or applyvacuum to the bottle until bubbles dissipate.11.4 Immediately analyze the sample with the automaticparticle counter according to the manufacturers operatinginstructions. Usually the analyzer is flushed with a specimen ofthe oil prior
30、to testing. After the initial flush, 2-3 runs on eachsample are recommended.11.5 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 recommendations.12. Report12.1 Report the average of the pa
31、rticle 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 11170. These particlesizes correspond approximately to 2, 5, 10, 15, 25, 50,and 100 m for particle counters that were
32、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 14m (c), as prescribed in ISO 4406:1999.13. Preci
33、sion and Bias13.1 Precision and bias statements based on interlaboratoryround robin testing will be determined within five years ofadoption of this standard method.14. Keywords14.1 optical particle counter; particle count; particulatecontamination4Available from National Institute of Standards and T
34、echnology, 100 BureauDrive, Gaithersburg, MD 20899.D 67862ASTM 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 pate
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37、earing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D 67863
