1、Designation: D 6698 07Standard Test Method forOn-Line Measurement of Turbidity Below 5 NTU in Water1This standard is issued under the fixed designation D 6698; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. 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 is applicable to the on-line measure-ment of turbidity under 5 nephelometric turbidity units (NTU)in water.1.2
3、It 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 method assigns traceable reporting units to the typ
4、eof respective technology that was used to perform the mea-surement. Units are numerically equivalent with respect to thecalibration standard. For example, a 1 NTU formazin standardis also equal to a 1FNU standard, a 1 FNRU standard and soforth.1.5 This standard does not purport to address all of th
5、esafety 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 Documents2.1 ASTM Standards:2D 1129 Terminology Relating
6、 to WaterD 1193 Specification for Reagent WaterD 1889 Test Method for Turbidity of Water3D 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 3864 Guide for Continual On-Line Monitoring Sy
7、stemsfor Water Analysis2.2 Other StandardsEPA 180.1 Methods for Chemical Analysis of Water andWastes, Turbidity4GLI Method 24Hach Method 8195 Determination of Turbidity byNephelometry EMMC Format5ISO 7027 Determination of Turbidity6Standard Method 2130B72.3 Other DocumentsUS Patent 4,283,1438US Pate
8、nt 4,291,9808US Patent 5,777,01153. Terminology3.1 DefinitionsFor definitions of terms used in thismethod refer to Terminology D 1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 calibration turbidity standarda turbidity standardthat is traceable and equivalent to the reference turbidity
9、standard to within statistical errors, including commerciallyprepared 4000 NTU Formazin, stabilized formazin, and sty-renedivinylbenzene (SDVB). These standards may be used tocalibrate the instrument.NOTE 1Calibration standards may be instrument specific.3.2.2 calibration verification standardsdefin
10、ed standardsused to verify the accuracy of a calibration in the measurementrange of interest. These standards may not be used to performcalibrations, only calibration verifications. Included standardsare opto-mechanical light scatter devices, gel-like standards, orany other type of stable liquid sta
11、ndard.1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.03 on Sampling Water andWater-Formed Deposits, Analysis of Water for Power Generation and Process Use,On-Line Water Analysis, and Surveillance of WaterCurrent edition
12、approved June 15, 2007. Published July 2007. Originallyapproved in 2001. Last previous edition approved in 2001 as D 6698 01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information,
13、refer to the standards Document Summary page onthe ASTM website.3Withdrawn.4Available from United States Environmental Protection Association (EPA),Ariel Rios Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20460, http:/www.epa.gov.5Hach Company, P.O. Box 389, Loveland, CO, 80539-0389, .6Available
14、 from International Organization for Standardization (ISO), 1 rue deVaremb, Case postale 56, CH-1211, Geneva 20, Switzerland, http:/www.iso.ch.7Standard Methods for the Examination of Water and Wastewater, 21st Edition,American Public HealthAssociation, Washington, DC, 2005, www.standardmethod-s.org
15、.8Available from AMCO Clear, P.O. Box 245, Powell, OH, 43065, www.amco-.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.NOTE 2Calibration verification standards may be instrument specific.3.2.3 in-situ nephelometera turbidimeter that
16、 determinesthe turbidity of a sample using a sensor that is placed directlyin the sample. This turbidimeter does not require transport ofthe sample to or from the sensor.3.2.4 nephelometric turbidity measurementthe measure-ment of light scatter from a sample in a direction that is at 90with respect
17、to the centerline of the incident light path. Unitsare NTU (Nephelometric Turbidity Units); when ISO 7027technology is employed, units are FNU (Formazin Nephelom-etric Units).3.2.5 ratio turbidity measurementthe measurement de-rived through the use of a nephelometric detector that serves asthe prima
18、ry detector and one or more other detectors used tocompensate for variation in incident light fluctuation, straylight, instrument noise, or sample color.3.2.6 reference turbidity standarda standard that is syn-thesized reproducibly from traceable raw materials by the user.All other standards are tra
19、ced back to this standard. Thereference standard for turbidity is formazin.3.2.7 seasoningthe process of conditioning labware withthe standard that will be diluted to a lower value. The processreduces contamination and dilution errors. See Appendix X2for suggested procedure.3.2.8 slip stream nephelo
20、meteran on-line turbidimeterthat determines the turbidity of a sample as the sample flowsthrough a sampling chamber. The sample is drawn from thesource into the turbidimeter, analyzed and then transported todrain.3.2.9 stray lightall light reaching the detector other thanthat contributed by the samp
21、le. For example: ambient lightleakage and divergent light in optical systems.3.2.10 turbidimeteran instrument that measures lightscatter using a nephelometric detector. Examples includephotoelectric nephelometers and ratio photoelectric nephelom-eters.3.2.11 turbidityan expression of the optical pro
22、perties of asample that causes light rays to be scattered and absorbedrather than transmitted in straight lines through the sample.(Turbidity of water is caused by the presence of matter such asclay, silt, finely divided organic matter, plankton, other micro-scopic organisms, organic acids, and dyes
23、.)4. Significance and Use4.1 Turbidity is undesirable in drinking water, plant effluentwaters, water for food and beverage processing, and for a largenumber of other water-dependent manufacturing processes.Removal of suspended matter is accomplished by coagulation,settling, and filtration. Measureme
24、nt of turbidity provides arapid means of process control to determine when, how, and towhat extent the water must be treated to meet specifications.4.2 This test method is suitable for the on-line monitoring ofturbidity such as that found in drinking water, process water,and high purity industrial w
25、aters.4.3 The instrumentation used must allow for the continuouson-line monitoring of a sample stream.NOTE 3See 7.2 for discussion on signal spikes resulting frombubbles.4.4 When reporting the measured result, appropriate unitsshould also be reported. The units are reflective of thetechnology used t
26、o generate the result, and if necessary,provide more adequate comparison to historical data sets.4.4.1 Table 1 describes technologies and reporting results.Those technologies listed are appropriate for the range ofmeasurement prescribed in this method are mentioned, thoughothers may come available.4
27、.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 subscripted wavelength value to characterizethe light source that was used.5. Safety5.1 Wear appropriate personal protection equipment at alltimes.5.2 Follo
28、w all relevant safety guidelines.5.3 Refer to instrument manuals for safety guidelines wheninstalling, calibrating, measuring or performing maintenancewith any of the respective instrumentation.5.4 Refer to all Material Safety Data Sheets (MSDSs) priorto preparing or using standards and before calib
29、rating orperforming instrument maintenance.6. Interferences6.1 Bubbles, color, and large suspended particles may resultin interferences. Bubbles cause positive interference and colorcauses negative interference. Dissolved material that imparts acolor to the water may cause errors in pure photoelectr
30、icnephelometric readings (versus ratio photoelectric nephelom-etric readings) unless the instrument has special compensatingfeatures. Certain turbulent motions also create unstable readingconditions of nephelometers.6.2 Scratches, finger marks, or dirt on any part of an opticalcomponent through whic
31、h light must travel to reach thesample, or through which scattered light leaves the sample to adetector, may give erroneous readings. Keep these surfacesscrupulously clean and replace damaged (etched or scratched)components.7. Apparatus7.1 The sensor used for the on-line monitoring of turbidityis de
32、signed for continuous monitoring of the turbidity of thesample stream.7.2 The instrument design should eliminate signal spikesresulting from bubbles present in samples through the use ofeither internal or external bubble rejection chambers (traps),sample pressurization, and/or electronic rejection m
33、ethods.7.3 The sensor must be designed to be calibrated. Thecalibration should be performed by following the manufactur-ers recommended procedures. If a calibration algorithm forthe instrument is used, it should be derived through the use ofa reference or calibration turbidity standard.7.4 The resol
34、ution of the instrument should permit detectionof turbidity differences of 0.01 NTU or less in waters havingturbidities 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.D66980727.5 Instrument Typ
35、esTwo types of instruments are avail-able for the nephelometric turbidity method, the nephelometerand ratio nephelometer.7.5.1 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 thein
36、tensity of light scattered at 90 to the centerline of the path ofthe incident light. The photoelectric nephelometer should be sodesigned that minimal stray light reaches the detector in theabsence of turbidity and should be free from significant driftafter a short warm-up period. The light source sh
37、ould be aTungsten lamp operated at a color temperature between 2200and 3000 K. Light Emitting Diodes (LEDs) and laser diodes indefined wavelengths ranging from 400-900 nm may also beused. If LEDs or laser diodes are used, then the LED or laserdiode should be coupled with a monitor detection device t
38、oachieve a consistent output. The total distance traversed byincident light and scattered light within the sample is not toexceed 10 cm. Angle of light acceptance to the detector:centered at 90 to the centerline of the incident light path andnot to exceed 610 from the 90 scatter path center line. Th
39、edetector must have a spectral response that is sensitive to thespectral output of the incident light used.7.5.1.1 Differences in physical design of photoelectricnephelometers will cause slight differences in measured valuesfor turbidity even though the same suspension is used forcalibrations. Compa
40、rability of measurements made using in-struments differing in optical and physical design is notrecommended. To minimize initial differences, observe thefollowing design criteria:7.5.2 Ratio Photoelectric Nephelometer(see Fig. 2 forsingle beam design; see Fig. 3 for multiple beam design). Thisinstru
41、ment uses the measurement derived through the use of anephelometric detector that serves as the primary detector andone or more other detectors used to compensate for variation inincident light fluctuation, stray light, instrument noise, orTABLE 1 Technologies and Reporting ResultsDesign and Reporti
42、ng Unit Prominent Application Key Design Features Typical 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.
43、0.020 to 40 Regulatory reportingof clean waterRatio White 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 ins
44、trument algorithmuses a combinationof detector readingsto 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
45、 color and goodfor low-level monitoring.Detector centered 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
46、 high levelsof color andfor monitoring tohigh turbidity levels.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
47、ISO 7027Regulatory reportingFormazin Nephelometric MultibeamUnit (FNMU)Is applicable toEPA regulatory method GLI Method 2.Applicable to drinkingwater and wastewatermonitoring applications.Detectors are geometricallycentered at 90 and 180.Uses a near-IR light source (780900 nm)monochromatic light sou
48、rce.An instrument algorithmuses a combination ofdetector readings, 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 sa
49、mples.Nephelometric method involvinga laser-based light sourceat 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 systemsD6698073sample color. As needed by the design, additional photodetec-tors may be used to sense the intensity of light scattered atother angles. The signals from these additional photodetectorsmay be used to compensate for variations in incident lightfluctuation, instrument stray lig
