1、Designation: D2144 07 (Reapproved 2013)Standard Practices forExamination of Electrical Insulating Oils by InfraredAbsorption1This standard is issued under the fixed designation D2144; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、 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 These practices are to be used for the recording andinterpretation of infrared absorption spectra of elec
3、trical insu-lating oils from 4000 to 400 cm1(2.5 to 25 m).NOTE 1While these practices are specific to ratio recording or opticalnull double-beam dispersive spectrophotometers, single-beam and HATR(horizontal attenuated total reflectance), Fourier-transform rapid scaninfrared spectrophotometers may a
4、lso be used. By computerized subtrac-tion techniques, ratio methods can be used. Any of these types ofequipment may be suitable if they comply with the specificationsdescribed in Practice E932.1.2 Two practices are covered, a Reference Standard Prac-tice and a Differential Practice.1.3 These practic
5、es are designed primarily for use as rapidcontinuity tests for identifying a shipment of oil from a supplierby comparing its spectrum with that obtained from previousshipments, or with the sample on which approval tests weremade. They also may be used for the detection of certain typesof contaminati
6、on in oils, and for the identification of oils instorage or service, by comparison of the spectra of theunknown and known oils.The practices are not intended for thedetermination of the various constituents of an oil.1.4 WarningInfrared absorption is a tool of high resolv-ing power. Conclusions as t
7、o continuity of oil quality shouldnot be drawn until sufficient data have been accumulated sothat the shipment-to-shipment variation is clearly established,for example.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This
8、 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 prior to use.2. Referenced Documents
9、2.1 ASTM Standards:2D923 Practices for Sampling Electrical Insulating LiquidsE131 Terminology Relating to Molecular SpectroscopyE168 Practices for General Techniques of Infrared Quanti-tative AnalysisE932 Practice for Describing and Measuring Performance ofDispersive Infrared Spectrometers3. Termino
10、logy3.1 DefinitionsFor definitions of terms and symbols, referto Terminology E131.4. Summary of Practices4.1 The infrared absorption spectrum may be recorded onthe spectrophotometer by either of the two practices outlinedbelow. In both practices differences in wavelength or frequencyand intensity of
11、 the absorption bands are observed and mea-sured.4.1.1 Reference Standard Practice An infrared cell filledwith the insulating oil test specimen is placed in the samplebeam of the spectrophotometer. With the shutter of the refer-ence beam open, the infrared absorption spectrum is recordedover the ent
12、ire range of the instrument. The absorption spec-trum of the test specimen is compared with a referencespectrum obtained with oil from a previous test specimen or thequalification oil.4.1.2 Differential PracticeTwo cells having the samesample path length are filled, one with the test specimen andthe
13、 other with the reference oil. The filled cells are then placedin the paths of the sample and reference beams, respectively,and the differential absorption spectrum recorded. This spec-trum is then compared with the reference differential spectrumobtained in a similar manner with the same cells fill
14、ed with thereference oil.1These practices are under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gases and are the direct responsibility ofSubcommittee D27.03 on Analytical Tests.Current edition approved Nov. 1, 2013. Published December 2013. Originallyapproved in 1963.
15、 Last previous edition approved in 2007 as D2144 07. DOI:10.1520/D2144-07R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page ont
16、he ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Significance and Use5.1 The infrared spectrum of an electrical insulating oil is arecord of the absorption of infrared energy over a range ofwavelengths. The spectrum
17、indicates the general chemicalcomposition of the test specimen.NOTE 2The infrared spectrum of a pure chemical compound isprobably the most characteristic property of that compound. However, inthe case of oils, multicomponent systems are being examined whosespectra are the sum total of all the spectr
18、a of the individual components.Because the absorption bands of the components may overlap, thespectrum of the oil is not as sharply defined as that for a single compound.For these reasons, these practices may not in every case be suitable for thequantitative estimation of the components of such a co
19、mplex mixture asmineral oil.6. Apparatus6.1 Infrared Spectrophotometer An infrared spectropho-tometer capable of operating within the 4000 to 400 cm1(2.5to 25-m) range in accordance with Practice E932.6.2 Absorption Cells Three types of cells may be used formeasuring the absorbance of electrical ins
20、ulating oils, namely(1) the sealed or fixed liquid cell, (2) the variable space cell,and ( 3) the demountable liquid cell. The use of the demount-able cell is not recommended for quantitative analysis. Usesealed fixed liquid and demountable liquid cells that meet therequirements of Practices E168. W
21、hen measuring the absor-bance of an oil by the Reference Standard Practice, a sealed orfixed cell having a sample path length of 0.1 6 0.014 mm isrecommended. Cells having a fixed path length of 0.2 6 0.028mm have been found to be acceptable. When the DifferentialPractice is used, two matched sealed
22、 or fixed cells each havinga sample path length of 0.050 6 0.007 mm are recommended.Where two matched cells are not available, a variable spacecell may be adjusted and used in place of one fixed cell. Withspectrophotometers having a range up to 16.7 m (600 cm1),liquid cells may be provided with sodi
23、um chloride (NaCl)windows. With instruments having a range up to 25 m (400cm1), use liquid cells with potassium bromide (KBr) windows.6.3 Cell Filling DeviceUse a glass hypodermic syringe of2 to 5-mL capacity or other suitable apparatus to fill the liquidcells.7. Sampling7.1 Obtain the sample in acc
24、ordance with Practices D923.8. Calibration8.1 Adjust and calibrate the spectrophotometer and cells inaccordance with Practice E932.9. Conditioning9.1 Store the sample in its original container and shield itfrom light. Allow the sealed container to stand undisturbed inthe room in which the test is to
25、 be made for a sufficient periodof time to permit the sample to attain room temperature beforeit is opened.9.2 Prior to taking specimens of transformer oil or lightcable oil, shake the sample container thoroughly and allow it tostand undisturbed for 15 min in order for all air bubbles to bedissipate
26、d from the sample. For heavy cable oils, gently tilt orinvert the sample container and swirl the fluid several timesand then permit it to stand undisturbed for 15 min.10. Cleaning, Storing, and Filling the Cell10.1 After the cells have been used, thoroughly rinse themwith a suitable reagent grade or
27、 functionally equivalent organicsolvent such as 2propanol (isopropyl alcohol) (care should beexercised to keep this solvent as dry as possible), followed byrinsing with a reagent grade or functionally equivalent hydro-carbon solvent, such as petroleum naphtha and store in adesiccator until they are
28、to be used.10.2 When a cell is to be used, clean it again as described in10.1 followed by two rinsings with the sample obtained fromthe middle portion of the fluid. Rinse the cell with a portion ofthe sample using the hypodermic syringe, which shall also becleaned prior to use in accordance with 10.
29、1.10.3 When filling the cell, fill the cleaned and rinsed syringewith about 2 mL of the test specimen. With the cell in theupright position and the TFE-fluorocarbon plugs removed fromthe ports in the cell, insert the syringe in the lower port andslowly fill the cell by exerting gradual pressure on t
30、he syringeplunger.When oil is observed flowing from the top port, lay thecell flat, remove the syringe, plug the lower port tightly, andplug the upper port loosely. (WarningApocket in some cellsmay secrete minute quantities of a previous test specimenwhich may contaminate the current test specimen a
31、nd causeerroneous results. Where this is suspected, dry the cell out aftercleaning and rinsing with a reagent grade or functionallyequivalent hydrocarbon solvent, such as petroleum naphtha,and by sweeping it with dry nitrogen applied at a pressure notexceeding 2.5 kPa (20 mm Hg) above ambient.)11. P
32、rocedureReference Standard Practice11.1 Fill a clean sealed or fixed cell having a sample pathlength of 0.10 6 0.014 mm (or 0.20 6 0.028 mm) with the testspecimen as outlined in Section 10 and place the filled cell inthe sample beam. Leave the shutter in the reference beam in theopen position. Adjus
33、t the scanning speed, gain, and othervariable controls to the values established for the particularspectrophotometer to provide the desired resolution. Where theinstrument is provided with a scale changer, it is recommendedthat it be used with the 2.5 to 1 ratio in preference to the linearmode in ob
34、taining recordings of the spectra. Record theinfrared spectrum over the entire range of the instrument inaccordance with Practices E168, using nonlinear absorbancecharts.11.2 Compare the infrared spectrum of the test specimenwith the reference spectrum of a test specimen from a previousshipment, or
35、the approved qualification oil, recorded by thesame procedure, using the same cell and with the sameinstrument settings. Comparison can be made by superimpos-ing the two spectra over a viewing light or by testing both testspecimens and recording the spectra on the same chart usingdifferent colored i
36、nks. Software techniques may also be usedfor this comparison. Note and record any differences in thewavelengths or frequencies of absorption bands and in appar-ent intensity of these bands. Differences between these spectraD2144 07 (2013)2can be amplified considerably by using an expanded ordinatesc
37、ale during the scanning.11.3 Measurements of the absorbance at specific absorptionbands, if required, are made by the base-line method describedin Practices E168 and corrected for thickness by expressing theresults as absorbance per millimetre.11.4 When using an FT-IR instrument, scan the atmosphere
38、at least three times with no cell in the instrument and store thisaveraged spectrum as the background. Place the cell containingthe test specimen in the instrument and again scan the spectrumat least three times. The resulting spectrum will be that of thetest specimen.12. ProcedureDifferential Pract
39、ice12.1 Fill two matched cells with the reference oil, eachhaving a path length of 0.050 6 0.007 mm; insert one cell inthe reference beam and the other in the sample beam. Adjustthe spectrophotometer as described in 11.1, set the pen positionat approximately 50 % transmission at 4000 cm1(2.5 m),and
40、record the differential infrared spectrum over the entirerange of the instrument, in accordance with Practices E168.Evidences of peaks (positive or negative) will be an indicationthat the cells are not matched or that the amplifier balance isnot properly adjusted.NOTE 3Peaks that are below the base
41、line are considered “positive”and those above the base line are “negative.”12.2 When two fixed matched cells having a sample pathlength of 0.050 6 0.007 mm are not available, a variable cellwhose sample path length can be adjusted to equal the pathlength of the fixed cell may be used. The procedure
42、foradjusting the sample path length of the variable cell is asfollows:12.2.1 Set the variable path length cell to the nominalthickness of the fixed path length liquid cell.12.2.2 Place the variable and fixed path length cells, bothfilled with the reference oil, in the paths of the reference andsampl
43、e beams, respectively.12.2.3 Close both beams of the spectrophotometer andadjust the electrical balance on the amplifier to no drift on therecorder pen.12.2.4 Set the pen position to approximately 90 % transmis-sion at 4000 cm1(2.5 m).12.2.5 Record the differential infrared spectrum over theentire r
44、ange of the instrument in accordance with PracticesE168.12.2.6 Adjust the path length of the variable cell untilabsorptions due to differences in sample path length are nolonger present; then repeat as in 12.2.5.12.3 With the same two matched cells with which thereference/reference differential spec
45、trum was recorded, fill onewith the reference oil and the other with the test specimen andinsert them in the paths of the reference and sample beams,respectively. Record the differential infrared spectrum over theentire range of the instrument in accordance with PracticesE168, using a nonlinear abso
46、rbance chart. Compare thereference/reference differential infrared spectrum obtained inaccordance with either 12.1 or 12.2 with the sample/referencedifferential infrared spectrum of this paragraph. Comparisoncan be made by recording on the same chart with a differentcolored ink or by superimposing t
47、he two spectra over a viewinglight. Note and record any differences in the wavelengths orfrequencies of absorption bands and in apparent intensity ofthese bands.NOTE 4This procedure is recommended to ensure that the recordingof spurious absorptions due to amplifier drift at zero energy null points a
48、renot erroneously assumed to be absorptions induced by differences incomposition.12.4 Measurements of the absorbance per millimetre, ifrequired, shall be made as described in 11.3.12.5 When using an FT-IR instrument, place the cell con-taining the reference oil in the instrument and scan thespectrum
49、 at least three times. Store the averaged spectrum asthe background. Remove the cell from the instrument, emptyand clean the cell. Fill the same cell with the test specimen ofoil and scan the spectrum at least three times. The resultingspectrum will now be the differential spectrum of the testspecimen of oil minus that of the reference specimen of oil.13. Calculation13.1 Convert measured absorbances and differences in ab-sorbance and report as absorbance per millimetre in order tocorrect for variations in the sample path length, within thetolerances prescr
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