1、Designation: D6698 12Standard Test Method forOn-Line Measurement of Turbidity Below 5 NTU in Water1This standard is issued under the fixed designation D6698; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. 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 is applicable to the on-line measure-ment of turbidity under 5 nephelometric turbidity units (NTU)in water.1.2 It
3、is the users responsibility to ensure the validity of thistest method for waters of untested matrices.1.3 In this test method calibration standards are defined inNTU values, but other assigned turbidity units are assumed tobe equivalent.1.4 This test method assigns traceable reporting units to thety
4、pe of respective technology that was used to perform themeasurement. Units are numerically equivalent with respect tothe calibration standard. For example, a 1 NTU formazinstandard is also equal to a 1 FNU (formazin nephelometricunits) standard, a 1 FNRU (formazin nephelometric ratio units)standard,
5、 and so forth.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 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
6、establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofAppli
7、cable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD3864 Guide for On-Line Monitoring Systems for WaterAnalysis2.2 Other Standards:EPA 180.1 Methods for Chemical Analysis of Water andWastes, Turbidity3GLI Method 24Hach Method 8195 Determination of Turb
8、idity by Nephelo-metry EMMC Format4ISO 7027 Determination of Turbidity5Standard Method 2130B62.3 Other Documents:7U.S. Patent 4,283,143 Patterson, James A. 1981. OpticalCharacterization of a Suspension. United States Patent4,283,143, filed November 19, 1979, and issued August11, 1981.U.S. Patent 4,2
9、91,980 Patterson, James A. 1981. Styrene-Divinylbenzene Copolymer and Method of Manufac-turer. United States Patent 4,291,980, filed August 14,1978, and issued September 29, 1981.U.S. Patent 5,777,011 Sadar, Michael J. 1998. StabilizedFormazin Composition. United States Patent 5,777,011,filed Decemb
10、er 1, 1995, and issued July 7, 1998.3. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 calibration turbidity standard, na turbidity standardthat is traceable and equivalent to the referenc
11、e turbiditystandard to within statistical errors; calibration turbidity stan-dard include commercially prepared 4000 NTU formazin,stabilized formazin, and styrenedivinylbenzene (SDVB).1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcom
12、mittee D19.03 on Sampling Water andWater-Formed Deposits, Analysis of Water for Power Generation and Process Use,On-Line Water Analysis, and Surveillance of Water.Current edition approved June 1, 2012. Published August 2013. Originallyapproved in 2001. Last previous edition approved in 2007 as D6698
13、 07. DOI:10.1520/D6698-12.2For 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 onthe ASTM website.3Available from United States Envir
14、onmental Protection Association (EPA),Ariel Rios Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20460, http:/www.epa.gov.4Available from Hach Company, P.O. Box 389, Loveland, CO, 80539-0389,http:/.5Available from International Organization for Standardization (ISO), 1 rue deVaremb, Case postale 5
15、6, CH-1211, Geneva 20, Switzerland, http:/www.iso.ch.6Available from Standard Methods for the Examination of Water andWastewater, 21st Edition, American Public Health Association, Washington, DC,2005, http:/www.standardmethods.org.7Available from AMCO Clear, P.O. Box 245, Powell, OH, 43065, http:/.C
16、opyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.1.1 DiscussionThese standards may be used to cali-brate the instrument. Calibration standards may be instrumentspecific.3.2.2 calibration verification standards, ndefined stan-dards u
17、sed to verify the accuracy of a calibration in themeasurement range of interest.3.2.2.1 DiscussionThese standards may not be used toperform calibrations, only calibration verifications. Includedstandards are opto-mechanical light scatter devices, gel-likestandards, or any other type of stable liquid
18、 standard. Calibra-tion verification standards may be instrument specific.3.2.3 in-situ nephelometer, na turbidimeter that deter-mines the turbidity of a sample using a sensor that is placeddirectly in the sample.3.2.3.1 DiscussionThis turbidimeter does not requiretransport of the sample to or from
19、the sensor.3.2.4 nephelometric turbidity measurement, nthe mea-surement of light scatter from a sample in a direction that is at90 with respect to the centerline of the incident light path.3.2.4.1 DiscussionUnits are NTU (nephelometric turbid-ity units); when ISO 7027 technology is employed, units a
20、reFNU (formazin nephelometric units).3.2.5 ratio turbidity measurement, nthe measurement de-rived through the use of a nephelometric detector that serves asthe primary detector and one or more other detectors used tocompensate for variation in incident light fluctuation, straylight, instrument noise
21、, or sample color.3.2.6 reference turbidity standard, na standard that issynthesized reproducibly from traceable raw materials by theuser.3.2.6.1 DiscussionAll other standards are traced back tothis standard. The reference standard for turbidity is formazin.3.2.7 seasoning, nthe process of condition
22、ing labwarewith the standard that will be diluted to a lower value.3.2.7.1 DiscussionThe process reduces contamination anddilution errors. See Appendix X2 for suggested procedure.3.2.8 slip stream nephelometer, nan on-line technique foranalysis of a sample as it flows through a measurementchamber of
23、 an instrument.3.2.8.1 Discussionthe sample is transported from thesource into the instrument (for example, a turbidimeter),analyzed, and then transported to drain or back to the processstream. The term is synonymous with the terms on-lineinstrument or continuous monitoring instrument.3.2.9 stray li
24、ght, nall light reaching the detector other thanthat contributed by the sample.3.2.9.1 DiscussionFor example: ambient light leakage anddivergent light in optical systems.3.2.10 turbidimeter, nan instrument that measures lightscatter caused by particulates within a sample and converts themeasurement
25、to a turbidity value.3.2.10.1 DiscussionThe detected light is quantitativelyconverted to a numeric value that is traced to a light scatterstandard.3.2.11 turbidity, nan expression of the optical propertiesof a sample that causes light rays to be scattered and absorbedrather than transmitted in strai
26、ght lines through the sample.3.2.11.1 DiscussionTurbidity of water is caused by thepresence of suspended and dissolved matter such as clay, silt,finely divided organic matter, plankton, other microscopicorganisms, organic acids, and dyes.4. Summary of Test Method4.1 The optical property expressed as
27、 turbidity is measuredby the scattering effect that suspended solids have on light; thehigher the intensity of scattered light, the higher the turbidity.In samples containing particulate matter, the manner in whichthe particulate matter interacts with light transmittance isrelated to the size, shape
28、 and composition of the particles in thewater, and also to the wavelength of the incident light.4.2 This test method is based upon a comparison of theintensity of light scattered by the sample with the intensity oflight scattered by a reference suspension. Turbidity values aredetermined by a nephelo
29、meter, which measures light scatterfrom a sample in a direction that is at 90 degrees with respectto the centerline of the incident light path.5. Significance and Use5.1 Turbidity is undesirable in drinking water, plant effluentwaters, water for food and beverage processing, and for a largenumber of
30、 other water-dependent manufacturing processes.Removal of suspended matter is accomplished by coagulation,settling, and filtration. Measurement of turbidity provides arapid means of process control to determine when, how, and towhat extent the water must be treated to meet specifications.5.2 This te
31、st method is suitable for the on-line monitoring ofturbidity such as that found in drinking water, process water,and high purity industrial waters.5.3 The instrumentation used must allow for the continuouson-line monitoring of a sample stream.NOTE 1See 8.2 for discussion on signal spikes resulting f
32、rom bubbles.5.4 When reporting the measured result, appropriate unitsshould also be reported. The units are reflective of thetechnology used to generate the result, and if necessary,provide more adequate comparison to historical data sets.5.4.1 Table 1 describes technologies and reporting results.Th
33、ose technologies listed are appropriate for the range ofmeasurement prescribed in this test method are mentioned,though others may come available.5.4.2 For a specific design that falls outside of the reportingranges in Table 1, the turbidity should be reported in turbidityunits (TU) with a subscript
34、ed wavelength value to characterizethe light source that was used.6. Safety6.1 Wear appropriate personal protection equipment at alltimes.6.2 Follow all relevant safety guidelines.D6698 1226.3 Refer to instrument manuals for safety guidelines wheninstalling, calibrating, measuring or performing main
35、tenancewith any of the respective instrumentation.6.4 Refer to all Material Safety Data Sheets (MSDSs) priorto preparing or using standards and before calibrating orperforming instrument maintenance.7. Interferences7.1 Bubbles, color, and large suspended particles may resultin interferences. Bubbles
36、 cause positive interference and colorcauses negative interference. Dissolved material that imparts acolor to the water may cause errors in pure photoelectricnephelometric readings (versus ratio photoelectric nephelomet-ric readings) unless the instrument has special compensatingfeatures. Certain tu
37、rbulent motions also create unstable readingconditions of nephelometers.7.2 Scratches, finger marks, or dirt on any part of an opticalcomponent through which light must travel to reach thesample, or through which scattered light leaves the sample to adetector, may give erroneous readings. Keep these
38、 surfacesscrupulously clean and replace damaged (etched or scratched)components.8. Apparatus8.1 The sensor used for the on-line monitoring of turbidityis designed for continuous monitoring of the turbidity of thesample stream.8.2 The instrument design should eliminate signal spikesresulting from bub
39、bles present in samples through the use ofeither internal or external bubble rejection chambers (traps),sample pressurization, or electronic rejection methods, or acombination thereof.TABLE 1 Technologies and Reporting ResultsDesign and Reporting Unit Prominent Application Key Design Features Typica
40、l Instrument Range Suggested ApplicationNephelometric non- ratio(NTU)White light turbidimeterscomply with EPA 180.1for low-levelturbidity monitoring.Detector centered at 90relative to the incidentlight beam. Uses a whitelight spectral source.0.020 to 40 Regulatory reportingof clean waterRatio White
41、Lightturbidimeters (NTRU)Complies with ISWTRregulations and StandardMethod 2130B.Can be used forboth low andhigh-level measurement.Used a white lightspectral source. Primarydetector centered at 90.Other detectors locatedat other angles.An instrument algorithmuses a combinationof detector readingsto
42、generate theturbidity reading.0.020 to 10 000 Regulatory Reportingof clean waterNephelometric, near-IRturbidimeters, non-ratiometric(FNU)Complies with ISO 7027.The wavelength isless susceptible tocolor interferences.Applicable for sampleswith color and goodfor low-level monitoring.Detector centered
43、at90 relative to theincident light beam.Uses a near-IR(780-900 nm) monochromaticlight source.0.012 to 1000 040 ISO 7027Regulatory reportingNephelometric near-IRturbidimeters, ratio metric(FNRU)Complies with ISO 7027.Applicable for sampleswith high levelsof color andfor monitoring tohigh turbidity le
44、vels.Uses a near-IRmonochromatic light source(780900 nm).Primary detector centeredat 90. Other detectorslocated at other angles.An instrument algorithmuses a combination ofdetector readings togenerate the turbidityreading.0.012 to 10 000 040 ISO 7027Regulatory reportingFormazin Nephelometric Mul-tib
45、eamUnit (FNMU)Is applicable toEPA regulatory method GLIMethod 2.Applicable to drinkingwater and wastewatermonitoring applications.Detectors are geometricallycentered at 0 and 90.Uses a near-IR light source(780900 nm)monochromatic light source.An instrument algorithmuses a combination ofdetector read
46、ings, whichmay differ forturbidities varying magnitude.0.012 to 4000 040 Reportingfor EPAand ISO compliancemNTU Is applicable toreporting of cleanwaters and filterperformance monitoring.Very sensitive toturbidity changes inlow turbidity samples.Nephelometric method involvinga laser-based light sourc
47、eat 660 nm anda high sensitivity photo-multpliertube (PMT) detectorfor light scatteredat 90.1000 mNTU=1NTU5 to 5000 mNTU 05000 mNTU,for EPA compliancereporting on drinkingwater systemsD6698 1238.3 The sensor must be designed to be calibrated. Thecalibration should be performed by following the manuf
48、actur-ers recommended procedures. If a calibration algorithm forthe instrument is used, it should be derived through the use ofa reference or calibration turbidity standard.8.4 The resolution of the instrument should permit detectionof turbidity differences of 0.01 NTU or less in waters havingturbid
49、ities of less than 1.00 NTU. The instrument shouldpermit detection of turbidity differences of 0.10 NTU or less inwaters with turbidity between 1.0 and 5.0 NTU.8.5 Instrument TypesTwo types of instruments are avail-able for the nephelometric turbidity method, the nephelometerand ratio nephelometer.8.5.1 The Photoelectric Nephelometer(See Fig. 1.) Thisinstrument uses a light source for illuminating the sample anda single photo-detector with a readout device to indicate theintensity of light scattered at 90
