1、Designation: G 138 06Standard Test Method forCalibration of a Spectroradiometer Using a Standard Sourceof Irradiance1This standard is issued under the fixed designation G 138; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONA standardized means of performing and reporting calibration of the spectroradiometer for spectralirradiance mea
3、surements is desirable.This test method presents specific technical requirements for a laboratory performing calibration ofa spectroradiometer for spectral irradiance measurements. A detailed procedure for performing thecalibration and reporting the results is outlined.This test method for calibrati
4、on is applicable to spectroradiometric systems consisting of at least amonochromator, input optics, and an optical radiation detector, and applies to spectroradiometriccalibrations performed with a standard of spectral irradiance with known irradiance values traceableto a national metrological labor
5、atory that has participated in intercomparisons of standards of spectralirradiance. The standard must also have known uncertainties and measurement geometry associatedwith its irradiance values.1. Scope1.1 This test method covers the calibration of spectroradi-ometers for the measurement of spectral
6、 irradiance using astandard of spectral irradiance that is traceable to a nationalmetrological laboratory that has participated in intercompari-sons of standards of spectral irradiance.1.2 This method is not limited by the input optics of thespectroradiometric system. However, choice of input optics
7、affects the overall uncertainty of the calibration.1.3 This method is not limited by the type of monochroma-tor or optical detector used in the spectroradiometer system.Parts of the method may not apply to determine which partsapply to the specific spectroradiometer being used. It isimportant that t
8、he choice of monochromator and detector beappropriate for the wavelength range of interest for thecalibration. Though the method generally applies to photo-diode array detector based systems, the user should note thatthese types of spectroradiometers often suffer from stray lightproblems and have li
9、mited dynamic range. Diode array spec-troradiometers are not recommended for use in the ultravioletrange unless these specific problems are addressed.1.4 The calibration described in this method employs theuse of a standard of spectral irradiance. The standard ofspectral irradiance must have known s
10、pectral irradiance valuesat given wavelengths for a specific input current and clearlydefined measurement geometry. Uncertainties must also beknown for the spectral irradiance values. The values assignedto this standard must be traceable to a national metrologicallaboratory that has participated in
11、intercomparisons of stan-dards of spectral irradiance. These standards may be obtainedfrom a number of national standards laboratories and commer-cial laboratories. The spectral irradiance standards consistmainly of tungsten halogen lamps with coiled filaments en-closed in a quartz envelope, though
12、other types of lamps areused. Standards can be obtained with calibration values cov-ering all or part of the wavelength range from 200 to 4500 nm.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 this stan
13、dard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.22. Referenced Documents2.1 ASTM Standards:3E 772 Terminology Relating to Solar Energy ConversionE 1341 Practice for Obtaining Spectroradiometric Data1This test method i
14、s under the jurisdiction of ASTM Committee G03 onDurability of Nonmetallic Materials and is the direct responsibility of SubcommitteeG03.09 on Ultraviolet Radiation Measurement Standards.Current edition approved June 1, 2006. Published July 2006. Originally approvedin 1996. Last previous edition app
15、roved in 2003 as G 138 03.2Available from Secretary, U.S. National Committee, CIE, National Institute ofStandards and Technology, Gaithersburg, MD 20899.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMSt
16、andards 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.from Radiant Sources for Colorimetry2.2 Other Documents:CIE Publication No. 634NIST Technical
17、 Note 1927: Guidelines for Evaluation andExpressing Uncertainty of NIST Measurement Results53. Terminology3.1 General terms pertaining to optical radiation and opticalmeasurement systems are defined in Terminology E 772. Someof the more important terms from that standard used in thispaper are listed
18、 here.3.1.1 bandwidth, nthe extent of a band of radiationreported as the difference between the two wavelengths atwhich the amount of radiation is half of its maximum over thegiven band.3.1.2 diffuser, na device used to scatter or disperse lightusually through the process of diffuse transmission or
19、reflec-tion.3.1.3 integrating sphere, na hollow sphere coated inter-nally with a white diffuse reflecting material and provided withseparate openings for incident and exiting radiation.3.1.4 irradiance, nradiant flux incident per unit area of asurface.3.1.5 monochromator, nwith respect to optical ra
20、diation,the restriction of the magnetic or electric field vector to a singleplane.3.1.6 polarization, nwith respect to optical radiation, therestriction of the magnetic or electric field vector to a singleplane.3.1.7 radiant flux, nthe time rate of flow of radiant energymeasured in watts.3.1.8 spect
21、ral irradiance, nirradiance per unit wavelengthinterval at a given wavelength.3.1.9 spectroradiometer, nan instrument for measuringthe radiant energy of a light source at each wavelengththroughout the spectrum.3.1.10 ultraviolet, adjoptical radiation at wavelengthsbelow 400 nanometres.3.2 Definition
22、s of Terms Specific to This Standard:3.2.1 calibration subsystems, nthe instruments used tosupply and monitor current to a standard lamp during calibra-tion, consisting of a DC power supply, a current shunt, and adigital voltmeter.3.2.2 passband, nthe effective bandwidth (c.f.), or spec-tral interva
23、l, over which the spectroradiometer system trans-mits at a given wavelength setting. Expressed as full-width atone-half maximum, as in bandwidth. A function of the lineardispersion (nm/mm) and slit or aperture widths (mm) of themonochromator system.3.2.3 primary standard of spectral irradiance, na b
24、roadspectrum light source with known spectral irradiance values atvarious wavelengths which are traceable to a national metro-logical laboratory that has participated in intercomparisons ofstandards of spectral irradiance.3.2.4 responsivity, nsymbol R = dS/df, S is signal fromspectroradiometer detec
25、tor, f is radiant flux at the detector.3.2.5 secondary standard of spectral irradiance, na stan-dard calibrated by reference to another standard such as aprimary or reference standard.3.2.6 slit scattering function, nsymbol Z (lo,l), the re-sponsivity of the combined detector and monochromator sys-t
26、em as a function of wavelengths, l, in the neighborhood of agiven wavelength setting, lo. The slit scattering function is thespectral responsivity in the neighborhood of specific wave-length setting, lo.3.2.7 spectral scattering (stray light), nlight with wave-lengths outside the passband of a spect
27、roradiometer a particularwavelength setting that is received by the detector and contrib-utes to the output signal.4. Significance and Use4.1 This method is intended for use by laboratories perform-ing calibration of a spectroradiometer for spectral irradiancemeasurements using a spectral irradiance
28、 standard of knownspectral irradiance values traceable to a national metrologicallaboratory that has participated in intercomparisons of stan-dards of spectral irradiance, known uncertainties and knownmeasurement geometry.4.2 This method is generalized to allow for the use ofdifferent types of input
29、 optics provided that those input opticsare suitable for the wavelength range and measurement geom-etry of the calibration.4.3 This method is generalized to allow for the use ofdifferent types of monochromators provided that they can beconfigured for a bandwidth, wavelength range, and throughputleve
30、ls suitable for the calibration being performed.4.4 This method is generalized to allow for the use ofdifferent types of optical radiation detectors provided that thespectral response of the detector over the wavelength range ofthe calibration is appropriate to the signal levels produced bythe monoc
31、hromator.5. Apparatus5.1 Laboratory:5.1.1 The room in which the calibrations are performed andespecially the area surrounding the optical bench should bedevoid of reflective surfaces. The calibration values assigned tothe spectral irradiance standard are for direct irradiance fromthe lamp and any ra
32、diation entering the monochromator fromsome other source including ambient reflections will be asource of error.5.1.2 The temperature and humidity in the laboratory shallbe maintained so as to agree with the conditions under whichthe calibrations of the spectral irradiance standard and thecalibratio
33、n subsystems were performed (typically 20C, 25C,50 % relative humidity).5.1.3 Air drafts in the laboratory should be minimized sincethey could affect the output of electrical discharge lamps.5.2 Spectroradiometer5.2.1 Monochromator:4Available from U.S. National Committee of the CIE (International Co
34、mmissionon Illumination), C/o Thomas M. Lemons, TLA-Lighting Consultants, Inc., 7 PondSt., Salem, MA 01970.5Available from American National Standards Institute, 11 West 42nd Street,13th Floor, New York, NY 10036G1380625.2.1.1 This can be a fixed or scanning, single or multiple,monochromator employi
35、ng holographic or ruled gratings orprisms or a combination of these dispersive elements. Forimproved performance in the ultraviolet (uv) portion of thespectrum, it is recommended that a scanning double mono-chromator be used to achieve lower stray light levels (see Fig.1). If the monochromator has i
36、nterchangeable slits, it isimportant that the manufacturer document the effective band-width of the monochromator with all possible combinations ofthe slits or that these bandwidths be determined experimen-tally. Configuration of the slits should be such that thebandpass function of the monochromato
37、r is symmetric, pref-erably triangular. The bandwidth should be constant across thewavelength region of interest and maintained between 85 %and 100 % of the measurement wavelength interval. Theprecision of the wavelength positioning of the monochromatorshould be 0.1 nm with an absolute accuracy of b
38、etter than 0.5nm (see Practice E 1341). For improved performance in the uv,it is recommended that high order rejection filters be inserted inthe optical path in the monochromator. The purpose of the highorder rejection filters is to block radiation in the monochroma-tor of unwanted wavelengths that
39、could otherwise overpowerthe signals being measured. The effects of variations intemperature and humidity on the performance of the mono-chromator should be addressed in writing by the manufacturer.5.2.1.2 Avoid mechanical shock and excessive vibration tothe monochromator. This can be facilitated by
40、 the use of avibration isolated lab table. If any optical parts in the mono-chromator are configurable by the user, refer to the manufac-turer precautions about opening the monochromator and han-dling any parts therein.5.2.2 Optical Radiation Detector:5.2.2.1 The optical radiation detector employed
41、by thespectroradiometer should be selected for optimal response overthe wavelength range of interest. It is also important that thedetector is sensitive enough to measure the levels of light thatwill be produced by the monochromator when it is configuredfor the calibration process. The active area o
42、f the detectorshould be evenly illuminated by the exit slit of the monochro-mator. A photomultiplier is typically used because of its highresponsivity and good signal-to-noise ratio. For this reason it isrecommended for use when measuring spectral irradiance inthe uv portion of the spectrum.5.2.2.2
43、The effects of variation in temperature and humidityon the response of the detector should be documented by themanufacturer. Of all components of the spectroradiometer, thedetector is usually the most sensitive to changes in tempera-ture. Some detectors may require cooling in order to maintaina spec
44、ific temperature.Avoid mechanical shock to the detector.If the detector requires an amplifier, any reported limitationsand uncertainties in the detector system must factor in thecontribution of the amplifier.5.2.3 If a diode array based spectroradiometer system isused, note the following recommendat
45、ions.5.2.3.1 The diode array spectroradiometer should employinternal focusing optics in the monochromator.5.2.3.2 When measuring in the ultraviolet, stray light shouldbe controlled by the use of high order rejection filters orinternal baffling, or both.5.2.3.3 The diode array spectroradiometer shoul
46、d not beused for measurements below 300 nm.5.2.4 Input Optics:FIG. 1 Typical Double Grating Monochromator LayoutG1380635.2.4.1 Some means of collecting the incident radiation andguiding it to evenly fill the entrance slit of the monochromatoris required. The input optics also can serve several other
47、important purposes.(1) Cosine ReceptorAn ideal cosine receptor will acceptall radiation from an entire hemisphere and sample radiant fluxaccording to the cosine of the incident angle.(2) DepolarizerThe components in the monochromatorare unfavorably affected by polarized light. A depolarizer canprodu
48、ce more consistent results from light sources of anypolarization type.(3) DiffuserA diffuser can remove hotspots from theincident radiation field and produce even illumination on theentrance slit.5.2.4.2 Reflective input optics are more desirable thantransmissive optics as they perform all three of
49、the functionspreviously discussed and are generally more useful over largerwavelength ranges. It is important to take into account theamount of attenuation caused by the input optics as this willaffect the signal levels at the detector. Ensure that the inputoptics are suitable for the wavelength range of interest. Thepredominant choice of input optics is the integrating sphere.5.3 Wide-band Cut-on and Cut-off Filters:5.3.1 Wideband cut-on and cut-off filters, also known aslong-pass or short-pass filters are needed to establish the levelof stray light in the mono
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