1、Designation: D7937 15Standard Test Method forIn-situ Determination of Turbidity Above 1 Turbidity Unit(TU) in Surface Water1This standard is issued under the fixed designation D7937; 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 This test method covers the in-situ field measurementsof turbidity in surface water. The measurement range
3、 is greaterthan 1 TU and the lesser of 10 000 TU or the maximummeasurable TU value specified by the turbidimeter manufac-turer.1.1.1 Precision data was conducted on both real world andsurrogate turbidity samples up to about 1000 TU. Many of thetechnologies listed in this test method are capable of m
4、easuringabove that provided in the precision section (see Section 16).1.2 “In-situ measurement” refers in this test method toapplications where the turbidimeter sensor is placed directly inthe surface water in the field and does not require transport ofa sample to or from the sensor. Surface water r
5、efers to springs,lakes, reservoirs, settling ponds, streams and rivers, estuaries,and the ocean.1.3 Many of the turbidity units and instrument designscovered in this test method are numerically equivalent incalibration when a common calibration standard is appliedacross those designs listed in Table
6、 1. Measurement of acommon calibration standard of a defined value will alsoproduce equivalent results across these technologies. This testmethod prescribes the assignment of a determined turbidityvalues to the technology used to determine those values.Numerical equivalence to turbidity standards is
7、 observedbetween different technologies but is not expected across acommon sample. Improved traceability beyond the scope ofthis test method may be practiced and would include the listingof the make and model number of the instrument used todetermine the turbidity values.1.4 In this test method, cal
8、ibration standards are oftendefined in NTU values, but the other assigned turbidity units,such as those in Table 1 are equivalent. For example,a1NTUformazin standard is alsoa1FNU,a1FAU,a1BU,andsoforth.1.5 This test method was tested on different natural watersand with standards that served as surrog
9、ates for samples. It isrecommended to validate the method response for waters ofuntested matrices.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 establish appro-priate safety and health
10、 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 ofApplicable Test Methods of Committee D19 on W
11、aterD3864 Guide for On-Line Monitoring Systems for WaterAnalysisD4411 Guide for Sampling Fluvial Sediment in MotionD7315 Test Method for Determination of Turbidity Above 1Turbidity Unit (TU) in Static ModeE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Cond
12、ucting an Interlaboratory Study toDetermine the Precision of a Test Method1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.07 on Sediments,Geomorphology, and Open-Channel Flow.Current edition approved Jan. 1, 2015. Publish
13、ed February 2015. DOI: 10.1520/D7937-15.2For 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.Copyright ASTM Intern
14、ational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1TABLE 1 Summary of Known in-situ Instrument Designs, Applications, Ranges, and Reporting UnitsDesign and Reporting Unit Prominent Application Key Design Features Typical Instrument Range Suggested Applicatio
15、n RangesNephelometric Non-Ratio (NTU) White light turbidimetersComply with EPA 180.1 for lowlevel turbidity monitoring.Detector centered at 90 rela-tive to the incident light beam.Uses a white light spectralsource.0.040 0.040 RegulatoryRatio White Light Turbidimeters(NTRU)Complies with U.S. EPA regu
16、la-tions and EPA 2130B. Can beused for both low and high levelmeasurement.Used a white light spectralsource. Primary detector cen-tered at 90. Other detectorslocated at other angles. An in-strument algorithm uses a com-bination of detector readings togenerate the turbidity reading.010 000 040 Regula
17、tory010 000 otherNephelometric, Near-IRTurbidimeters, Non- Ratiometric(FNU)Complies with ISO 7027. Thewavelength is less susceptibleto color interferences. Appli-cable for samples with colorand good for low level monitor-ing.Detector centered at 90 rela-tive to the incident light beam.Uses a near-IR
18、 (780-900 nm)monochromatic light source.01 000 040 Regulatory (non-US)01 000 otherNephelometric Near-IRTurbidimeters, Ratio Metric(FNRU)Complies with ISO 7027. Appli-cable for samples with high lev-els of color and for monitoringto high turbidity levels.Uses a near-IR monochromaticlight source (7809
19、00 nm). Pri-mary detector centered at 90.Other detectors located at otherangles. An instrument algorithmuses a combination of detectorreadings to generate the turbid-ity reading.010 000 040 Regulatory010 000 otherFormazin Back Scatter (FBU) Not applicable for regulatorypurposes. Best applied to high
20、turbidity samples. Backscatteris common probe technologyand is best applied in higherturbidity samples.Uses a near-IR monochromaticlight source in the 780900 nmrange. Detector geometry is 30 15 relative to the incidentlight beam.10010 000+ 10010 000Backscatter Unit (BU) Not applicable for regulatory
21、purposes. Best applied forsamples with high level turbidid-ity.Uses a white light spectralsource (400680 nm range).Detector geometry is 30 15relative to the incident lightbeam.1010 000+ 10010 000+Formazin Attenuation Unit(FAU)May be applicable for someregulatory purposes. This iscommonly applied wit
22、h spectro-photometers. Best applied forsamples with high level turbidid-ity.Detector is geometrically cen-tered at 180 relative to incidentbeam (attenuation) Wavelengthis 780900 nm.201 000 201 000 RegulatoryLight Attenuation Unit (AU) Not applicable for some regula-tory purposes. This is com-monly a
23、pplied with spectropho-tometers.Detector is geometrically cen-tered at 180 relative to incidentbeam (attenuation). Wavelengthis 400680 nm.201 000 201 000Nephelometric Turbidity Multi-beam Unit (FNMU)Is applicable to EPA regulatorymethod GLI Method 2. Appli-cable to drinking water andwastewater monit
24、oring applica-tions.Detectors are geometricallycentered at 90 and 180. Aninstrument algorithm uses acombination of detectorreadings, which may differ forturbidities varying magnitude.0.024000 040 Regulatory04 000 otherForward Scatter Ratio Unit(FSRU)The technology encompasses asingle, light source a
25、nd two de-tectors. Light sources can varyfrom single wavelength to poly-chromatic sources. The detec-tion angle for the forward scat-ter detector is between 0 and90 relative to the centerline ofthe incident light beam.The technology is sensitive toturbidities as low as 1 TU. Theratio technology help
26、s to com-pensate for color interferenceand fouling.1-800 FSRUThe measurement of ambientwaters such as streams, lakes,rivers.Forward Scatter Ratio Unit(FSRU)Forward Scatter Unit (FSU) The technology encompasses asingle, light source and one de-tector between 0 and 90 rela-tive to the centerline of th
27、e inci-dent light beam.The technology is sensitive toturbidities as low as 1 TU. Theratio technology helps to com-pensate for color interferenceand fouling.1-1000 FSUThe measurement of ambientwaters such as streams, lakes,rivers and process waters.Forward Scatter Unit (FSU)D7937 1522.2 Other Referen
28、ced Standards:EPA 180.1 Determination of Turbidity by Nephelometry3EPA 2130B Analytical Method For Turbidity Measurement3ISO 7027 (International Organization for Standardization)Water Quality for the Determination of Turbidity4GLI Method 2 Turbidity33. Terminology3.1 DefinitionsFor definitions of te
29、rms used in this testmethod, refer to Terminology D1129.3.2 Definitions of Terms Specific to This StandardUnlessotherwise noted, the term light means visible light or near-infrared (NIR) radiation or both.3.2.1 ambient light, nlight or optical path or both that doesnot originate from the light sourc
30、e of a turbidimeter.3.2.2 attenuation, nthe amount of incident light that isscattered and absorbed before reaching a detector, which isgeometrically centered at 180 relative to the centerline of theincident light beam.3.2.2.1 DiscussionAttenuation is inversely proportional totransmitted signal.Atten
31、uated Turbidity = Absorbed Light + Scattered Light3.2.2.2 DiscussionThe application of attenuation in thistest method is as a distinct means of measuring turbidity. Whenmeasured in the FAU or AU mode, the turbidity value is acombination of scattered (attenuated) light plus absorbed light.The scatter
32、ed light is affected by particle size and is a positiveresponse. The absorption due to color is a negative response.The sum of these two responses results in the turbidity value inthe appropriate unit.3.2.3 automatic power control (APC), nthe regulation oflight power from a source such that illumina
33、tion of the sampleremains constant with time and temperature.3.2.4 broadband, white-light source, na visible-lightsource that has a full bandwidth at half of the sourcesmaximum intensity (FWHM) located at wavelengths greaterthan 200 nm.3.2.4.1 DiscussionTungsten-filament lamps (TFLs) andwhite LEDs a
34、re examples of broadband sources.3.2.5 calibration turbidity standard, na turbidity standardthat is traceable and equivalent to the reference turbiditystandard to within defined accuracy; commercially prepared4000 NTU Formazin, stabilized formazin, and styrenedivinyl-benzene (SDVB) are calibration t
35、urbidity standards.3.2.5.1 DiscussionThese standards may be used to cali-brate the instrument. All meters should read equivalent valuesfor formazin standards. SDVB-standard readings are instru-ment specific and should not be used on meters that do not havedefined values specified for that instrument
36、. Calibration stan-dards that exceed 10 000 turbidity units are commerciallyavailable.3.2.6 calibration-verification standards, ndefined stan-dards used to verify the instrument performance in the mea-surement range of interest.3.2.6.1 DiscussionCalibration-verification standards maynot be used to a
37、djust instrument calibration, but only to checkthat the instrument measurements are in the expected range.Examples of calibration-verification standards are opto-mechanical light-scatter devices, gel-like standards, or anyother type of stable liquid standard. Calibration-verificationstandards may be
38、 instrument-design specific.3.2.7 color, nthe hue (red, yellow, blue, etc.) of a watersample produced by the combination of: the selective absorp-tion of visible light, the spectral reflectivity, and the degree ofdarkness or blackness of suspended matter.3.2.7.1 DiscussionThe combination above is de
39、fined bythe Munsell (1)5color-classification scheme.3.2.8 detector, na solid-state device that converts lightinto electrical current or voltage.3.2.9 detector angle, nthe angle between the axis of thedetector acceptance cone and the axis of the source light orNIR beam.3.2.9.1 DiscussionThe detector
40、angle equals 180 ( isthe scattering angle).3.2.10 narrow-band source, na light source with a fullbandwidth (at half of the sources maximum intensity)(FWHM) located at wavelengths less than 5 nm.3.2.11 operating spectrum, nthe wavelength-by-wavelength products of source intensity, filter transmittanc
41、e,and detector sensitivity.3.2.11.1 DiscussionThe operating spectrum determinesthe relative contributions of wavelengths in the light-to-currentconversions made by a turbidimeter.3.2.12 ratio turbidity measurement, nthe measurementderived through the use of a primary detector and one or moreother de
42、tectors to compensate for variation in incident-lightintensity, stray light, sample color, window transmittance, anddissolved NIR-absorbing matter.3.2.13 reference turbidity standard, na standard that issynthesized reproducibly from traceable raw materials by askilled analyst.3.2.13.1 DiscussionAll
43、other standards are traced back tothis standard. The reference standard for turbidity is formazin.3.2.14 sample volume, nthe water-sample volumewherein light from a turbidimeter source interacts with sus-pended particles and is subsequently detected.3.2.15 scattering (also referred to as scatter), n
44、lightinteraction that alters the direction of light transport through asample without changing the wavelength.3.2.15.1 DiscussionThe light interaction can be with sus-pended particles, water molecules, and variations in the sam-ples refractive index.3.2.16 scattering angle (), nthe angle between a s
45、ourcelight or NIR beam, and the scattered beam.3Available from United States Environmental ProtectionAgency (EPA), WilliamJefferson Clinton Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20004,http:/www.epa.gov.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor
46、, New York, NY 10036, http:/www.ansi.org.5The boldface numbers in parentheses refer to the list of references at the end ofthis standard.D7937 1533.2.17 forward-scattered radiation, nthe scattered inci-dent light that is detected at an angle between 0-degrees andless than 90-degrees, relative to the
47、 direction of the projectedincident-light beam.3.2.17.1 DiscussionMost designs will have an angle be-tween 0-degrees and 45-degrees.3.2.18 stray light, nall light reaching the detector(s) otherthan light that is scattered by the sample.3.2.18.1 DiscussionStray light could be ambient-lightleakage, in
48、ternal reflections, and divergent light in opticalsystems. For this test method, stray light is likely to benegligible. The instrument design is intended to reduce oreliminate stray light.3.2.19 transmittance, nthe ratio of light power transmittedthrough a sample to the light power incident upon the
49、 sample.3.2.20 turbidimeter design, nan arrangement of optical(lenses, windows, filters, apertures, etc.) and optoelectronic(light sources and detectors, etc.) components, mechanicalcomponents, and electrical circuits for determining the turbid-ity of water.3.2.21 turbidity, nan expression of a samples opticalproperties that cause light rays to be scattered and absorbedrather than transmitted in straight lines through the sample.3.2.21.1 DiscussionTurbidity of water is caused by thepresence
