1、Designation: D 2144 07Standard Practices forExamination of Electrical Insulating Oils by InfraredAbsorption1This standard is issued under the fixed designation D 2144; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t 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 These practices are to be used for the recording andinterpretation of infrared absorption spectra of electrical insu-lat
3、ing 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 also be used. By
4、 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 E 932.1.2 Two practices are covered, a Reference Standard Prac-tice and a Differential Practice.1.3 These practices are designe
5、d 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 contamination in oils, an
6、d 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 to continuity o
7、f oil quality shouldnot be drawn until sufficient data have been accumulated sothat the shipment-to-shipment variation is clearly established,for example.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of t
8、his 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:2D 923 Practices for Sampling Electrical Insulating LiquidsE 131 Terminology Relating to Molecular SpectroscopyE 168 Pr
9、actices for General Techniques of Infrared Quanti-tative AnalysisE 932 Practice for Describing and Measuring Performanceof Dispersive Infrared Spectrometers3. Terminology3.1 DefinitionsFor definitions of terms and symbols, referto Terminology E 131.4. Summary of Practices4.1 The infrared absorption
10、spectrum may be recorded onthe spectrophotometer by either of the two practices outlinedbelow. In both practices differences in wavelength or frequencyand intensity of the absorption bands are observed and mea-sured.4.1.1 Reference Standard PracticeAn infrared cell filledwith the insulating oil test
11、 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 entire range of the instrument. The absorption spec-trum of the test specimen is compared with a referencespectrum obtained with oil from
12、 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 and1These practices are under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gases and are the direct responsibi
13、lity ofSubcommittee D27.03 on Analytical Tests.Current edition approved May 1, 2007. Published June 2007. Originallyapproved in 1963. Last previous edition approved in 2001 as D 2144 01e1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service
14、astm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the other with the reference oil. The filled cells are the
15、n 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 filled with thereference oil.5. Significance and Use5.1 The
16、 infrared spectrum of an electrical insulating oil is arecord of the absorption of infrared energy over a range ofwavelengths. The spectrum indicates the general chemicalcomposition of the test specimen.NOTE 2The infrared spectrum of a pure chemical compound isprobably the most characteristic proper
17、ty of that compound. However, inthe case of oils, multicomponent systems are being examined whosespectra are the sum total of all the spectra 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
18、 compound.For these reasons, these practices may not in every case be suitable for thequantitative estimation of the components of such a complex mixture asmineral oil.6. Apparatus6.1 Infrared SpectrophotometerAn infrared spectropho-tometer capable of operating within the 4000 to 400 cm1(2.5to 25-m)
19、 range in accordance with Practice E 932.6.2 Absorption CellsThree types of cells may be used formeasuring the absorbance of electrical insulating 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
20、 recommended for quantitative analysis. Usesealed fixed liquid and demountable liquid cells that meet therequirements of Practices E 168. When 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. Ce
21、lls 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 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 adjust
22、ed 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 sodium chloride (NaCl)windows. With instruments having a range up to 25 m (400cm1), use liquid cells with potassium bromide (KBr) win-dows.6.3 Cell Filling DeviceUse
23、 a glass hypodermic syringe of2 to 5-mL capacity or other suitable apparatus to fill the liquidcells.7. Sampling7.1 Obtain the sample in accordance with Practices D 923.8. Calibration8.1 Adjust and calibrate the spectrophotometer and cells inaccordance with Practice E 932.9. Conditioning9.1 Store th
24、e sample in its original container and shield itfrom light. Allow the sealed container to stand undisturbed inthe room in which the test is to 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
25、 lightcable oil, shake the sample container thoroughly and allow it tostand undisturbed for 15 min in order for all air bubbles to bedissipated 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 fo
26、r 15 min.10. Cleaning, Storing, and Filling the Cell10.1 After the cells have been used, thoroughly rinse themwith a suitable reagent grade or functionally equivalent organicsolvent such as 2propanol (isopropyl alcohol) (care should beexercised to keep this solvent as dry as possible), followed byri
27、nsing with a reagent grade or functionally equivalent hydro-carbon solvent, such as petroleum naphtha and store in adesiccator until they are 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
28、fluid. Rinse the cell with a portion ofthe sample using the hypodermic syringe, which shall also becleaned prior to use in accordance with 10.1.10.3 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-fluoro
29、carbon plugs removed fromthe ports in the cell, insert the syringe in the lower port andslowly fill the cell by exerting gradual pressure on the 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 lo
30、osely. (WarningApocket in some cellsmay secrete minute quantities of a previous test specimenwhich may contaminate the current test specimen and causeerroneous results. Where this is suspected, dry the cell out aftercleaning and rinsing with a reagent grade or functionallyequivalent hydrocarbon solv
31、ent, 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. ProcedureReference 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 testspec
32、imen as outlined in Section 10 and place the filled cell inthe sample beam. Leave the shutter in the reference beam in theopen position. Adjust the scanning speed, gain, and othervariable controls to the values established for the particularspectrophotometer to provide the desired resolution. Where
33、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 obtaining recordings of the spectra. Record theinfrared spectrum over the entire range of the instrument inaccordance with Practices E 168, using nonlinear abso
34、rbancecharts.11.2 Compare the infrared spectrum of the test specimenwith the reference spectrum of a test specimen from a previousshipment, or the approved qualification oil, recorded by thesame procedure, using the same cell and with the sameinstrument settings. Comparison can be made by superimpos
35、-ing the two spectra over a viewing light or by testing both testD 2144 072specimens and recording the spectra on the same chart usingdifferent colored inks. Software techniques may also be usedfor this comparison. Note and record any differences in thewavelengths or frequencies of absorption bands
36、and in appar-ent intensity of these bands. Differences between these spectracan be amplified considerably by using an expanded ordinatescale during the scanning.11.3 Measurements of the absorbance at specific absorptionbands, if required, are made by the base-line method describedin Practices E 168
37、and corrected for thickness by expressingthe results as absorbance per millimetre.11.4 When using an FT-IR instrument, scan the atmosphereat least three times with no cell in the instrument and store thisaveraged spectrum as the background. Place the cell containingthe test specimen in the instrumen
38、t and again scan the spectrumat least three times. The resulting spectrum will be that of thetest specimen.12. ProcedureDifferential Practice12.1 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 sam
39、ple beam. Adjustthe spectrophotometer as described in 11.1, set the pen positionat approximately 50 % transmission at 4000 cm1(2.5 m), andrecord the differential infrared spectrum over the entire rangeof the instrument, in accordance with Practices E 168. Evi-dences of peaks (positive or negative) w
40、ill be an indication thatthe cells are not matched or that the amplifier balance is notproperly adjusted.NOTE 3Peaks that are below the base 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
41、 not available, a variable cellwhose sample path length can be adjusted to equal the pathlength of the fixed cell may be used. The procedure 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
42、 liquid cell.12.2.2 Place the variable and fixed path length cells, bothfilled with the reference oil, in the paths of the reference andsample 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
43、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 range of the instrument in accordance with PracticesE 168.12.2.6 Adjust the path length of the variable cell untilabsorptions due to differences in sample path
44、length are nolonger present; then repeat as in 12.2.5.12.3 With the same two matched cells with which thereference/reference differential spectrum 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,respectiv
45、ely. Record the differential infrared spectrum over theentire range of the instrument in accordance with PracticesE 168, using a nonlinear absorbance chart. Compare thereference/reference differential infrared spectrum obtained inaccordance with either 12.1 or 12.2 with the sample/referencedifferent
46、ial infrared spectrum of this paragraph. Comparisoncan be made by recording on the same chart with a differentcolored ink or by superimposing the two spectra over a viewinglight. Note and record any differences in the wavelengths orfrequencies of absorption bands and in apparent intensity ofthese ba
47、nds.NOTE 4This procedure is recommended to ensure that the recordingof spurious absorptions due to amplifier drift at zero energy null points arenot erroneously assumed to be absorptions induced by differences incomposition.12.4 Measurements of the absorbance per millimetre, ifrequired, shall be mad
48、e 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 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 th
49、e 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 prescribed for the cells. Absorbance may not be alinear function of sample path length over a wide range of celllengths; therefore strictly adhere to the cell sizes
