1、Designation: E2847 11Standard Practice forCalibration and Accuracy Verification of Wideband InfraredThermometers1This standard is issued under the fixed designation E2847; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、 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 guide covers electronic instruments intended formeasurement of temperature by detecting the intensity ofthermal
3、radiation exchanged between the subject of measure-ment and the sensor.1.2 The devices covered by this guide are referred to asinfrared thermometers in this document.1.3 The infrared thermometers covered in this guide areinstruments that are intended to measure temperatures below1000C, measure therm
4、al radiation over a wide bandwidth inthe infrared region, and are direct-reading in temperature.1.4 This guide covers best practice in calibrating infraredthermometers. It addresses concerns that will help the userperform more accurate calibrations. It also provides a structurefor calculation of unc
5、ertainties and reporting of calibrationresults to include uncertainty.1.5 Details on the design and construction of infraredthermometers are not covered in this guide.1.6 This guide does not cover infrared thermometry above1000C. It does not address the use of narrowband infraredthermometers or infr
6、ared thermometers that do not indicatetemperature directly.1.7 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.8 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathema
7、ticalconversions to SI units that are provided for information onlyand are not considered standard.2. Referenced Documents2.1 ASTM Standards:2E344 Terminology Relating to Thermometry and Hydrom-etryE1256 Test Methods for Radiation Thermometers (SingleWaveband Type)E2758 Guide for Selection and Use o
8、f Wideband, LowTemperature Infrared Thermometers3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 cavity bottom, nthe portion of the cavity radiationsource forming the end of the cavity.3.1.1.1 DiscussionThe cavity bottom is the primary areawhere an infrared thermometer being ca
9、librated measuresradiation.3.1.2 cavity radiation source, na concave shaped geom-etry approximating a perfect blackbody of controlled tempera-ture and defined emissivity used for calibration of radiationthermometers.3.1.2.1 DiscussionA cavity radiation source is a subset ofthermal radiation sources.
10、3.1.2.2 DiscussionTo be a cavity radiation source ofpractical value for calibration, at least 90 % of the field-of-viewof a radiation thermometer is expected to be incident on thecavity bottom. In addition, the ratio of the length of the cavityversus the cavity diameter is expected to be greater tha
11、n orequal to 5:1.3.1.3 cavity walls, nthe inside surfaces of the concaveshape forming a cavity radiation source.3.1.4 customer, nthe individual or institution to whom thecalibration or accuracy verification is being provided.3.1.5 distance-to-size ratio (D:S), nsee field-of-view.3.1.6 effective emis
12、sivity, nthe ratio of the amount ofenergy over a given spectral band exiting a thermal radiationsource to that predicted by Plancks Law at a given tempera-ture.3.1.7 field-of-view, na usually circular, flat surface of ameasured object from which the radiation thermometer re-ceives radiation. (1)31Th
13、is practice is under the jurisdiction ofASTM Committee E20 on TemperatureMeasurement and is the direct responsibility of Subcommittee E20.02 on RadiationThermometry.Current edition approved Nov. 1, 2011. Published April 2012. DOI: 10.1520/E284711.2For referenced ASTM standards, visit the ASTM websit
14、e, 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.3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.1Copyright ASTM Inte
15、rnational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.7.1 DiscussionMany handheld infrared thermometersmanufacturers include distance-to-size ratio (D:S) in theirspecifications. Distance-to-size ratio relates to the followingphysical situation: at a given
16、 distance (D), the infrared ther-mometer measures a size (S) or diameter, and a certainpercentage of the thermal radiation received by the infraredthermometer is within this size. Field-of-view is a measure ofthe property described by distance-to-size ratio. (1)3.1.8 flat-plate radiation source, na
17、planar surface ofcontrolled temperature and defined emissivity used for calibra-tions of radiation thermometers.3.1.8.1 DiscussionA flat-plate radiation source is a subsetof thermal radiation sources.3.1.9 measuring temperature range, ntemperature rangefor which the radiation thermometer is designed
18、. (1)3.1.10 purge, na process that uses a dry gas to remove thepossibility of vapor on a measuring surface.3.1.11 radiance temperature, ntemperature of an ideal (orperfect) blackbody radiator having the same radiance over agiven spectral band as that of the surface being measured. (2)3.1.12 thermal
19、radiation source, na geometrically shapedobject of controlled temperature and defined emissivity usedfor calibration of radiation thermometers.3.1.13 usage temperature range, ntemperature range forwhich a radiation thermometer is designed to be utilized by theend user.4. Summary of Practice4.1 The p
20、ractice consists of comparing the readout tempera-ture of an infrared thermometer to the radiance temperature ofa radiation source. The radiance temperature shall correspondto the spectral range of the infrared thermometer under test.4.2 The radiation source may be of two types. Ideally, thesource w
21、ill be a cavity source having an emissivity close tounity (1.00). However, because the field-of-view of someinfrared thermometers is larger than typical blackbody cavityapertures, a large-area flat-plate source may be used for thesecalibrations. In either case, the traceable measurement of theradian
22、ce temperature of the source shall be known, along withcalculated uncertainties.4.3 The radiance temperature of the source shall be trace-able to a national metrology institute such as the NationalInstitute of Standards and Technology (NIST) in Gaithersburg,Maryland or the National Research Council
23、(NRC) in Ottawa,Ontario, Canada.5. Significance and Use5.1 This guide provides guidelines and basic test methodsfor the accuracy verification of infrared thermometers. Itincludes test set-up and calculation of uncertainties. It isintended to provide the user with a consistent method, whileremaining
24、flexible in the choice of calibration equipment. It isunderstood that the uncertainty obtained depends in large partupon the apparatus and instrumentation used. Therefore, sincethis guide is not prescriptive in approach, it provides detailedinstruction in uncertainty evaluation to accommodate thevar
25、iety of apparatus and instrumentation that may be em-ployed.5.2 This guide is intended primarily for calibrating handheldinfrared thermometers. However, the techniques described inthis guide may also be appropriate for calibrating other classesof radiation thermometers. It may also be of help to tho
26、secalibrating thermal imagers.5.3 This guide specifies the necessary elements of the reportof calibration for an infrared thermometer. The requiredelements are intended as a communication tool to help the enduser of these instruments make accurate measurements. Theelements also provide enough inform
27、ation, so that the results ofthe calibration can be reproduced in a separate laboratory.6. Sources of Uncertainty6.1 Uncertainties are present in all calibrations. Uncertain-ties are underestimated when their effects are underestimatedor omitted. The predominant sources of uncertainty are de-scribed
28、 in Section 10 and are listed in Table 1 and Table X1.1of Appendix X1.6.2 Typically, the most prevalent sources of uncertainties inthis method of calibration are: (1) emissivity estimation of thecalibration source, (2) size-of-source of the infrared thermom-eter, (3) temperature gradients on the rad
29、iation source, (4)improper alignment of the infrared thermometer with respect tothe radiation source, (5) calibration temperature of the radia-tion source, (6) ambient temperature and (7) reflected tempera-ture. The order of prevalence of these uncertainties may vary,depending on use of proper proce
30、dure and the type of thermalradiation source used. Depending on the temperature of theradiation source, the calibration method of the radiation source,the optical characteristics of the infrared thermometer and thedetector and filter characteristics of the infrared thermometer,the contribution of th
31、ese uncertainties may change significantlyin the overall uncertainty budget.7. Apparatus7.1 Thermal Radiation Source:7.1.1 There are two different classes of thermal radiationsources which can be used for infrared thermometer calibra-tions: a cavity source and a flat-plate source. Some sourcesmay be
32、 considered a hybrid of both categories. Each of thesesources has advantages and disadvantages. The cavity sourceprovides a source of radiation that has a more predictableemissivity. However, the flat-plate source can usually be madeless expensively, can be made with a diameter large enough toTABLE
33、1 Components of UncertaintyUncertainty Component Discussion Evaluation MethodSource UncertaintiesU1Calibration Temperature 10.4 10.4.1U2Source Emissivity 10.5 10.2.3, X2.4 (example)U3Reflected Ambient Radiation 10.6 10.2.2, X2.5 (example)U4Source Heat Exchange 10.7 10.7.1U5Ambient Conditions 10.8 10
34、.8.1U6Source Uniformity 10.9 10.9.1Infrared Thermometer UncertaintiesU7Size-of-Source Effect 10.11 Test Methods E1256U8Ambient Temperature 10.12 Appendix X3U9Atmospheric Absorption 10.13 X2.3U10Noise 10.14 10.14.1U11Display Resolution 10.15 10.15.2E2847 112calibrate infrared thermometers with low di
35、stance to size ratios(D:S), and may geometrically more resemble the surfacemeasured by the infrared thermometer when in use in the field.7.1.2 Ideally, the size of the thermal radiation source shouldbe specified by the infrared thermometer manufacturer. Inmany cases, this information may not be avai
36、lable. In thesecases a field-of-view test should be completed as discussed inE1256. The portion of signal incident on the infrared thermom-eter that does not come from the source should be accountedfor in the uncertainty budget.7.1.3 Cavity Source:7.1.3.1 A cavity source can be constructed in severa
37、l shapesas shown in Fig. 1. In general, a high length-to-diameter ratio(L:D) or radius-to-diameter ratio (R:D) in the spherical casewill result in a smaller uncertainty. A smaller conical angle Fwill also result in a smaller uncertainty.7.1.3.2 The location of a reference or a control probe, orboth,
38、 and the thermal conductivity of the cavity walls areimportant considerations in cavity source construction. Ingeneral, a reference or control probe should be as close aspractical to the center of the area where the infrared thermom-eter will typically measure, typically the cavity bottom. If therei
39、s a separation between the location of the reference probe andthe cavity surface, cavity walls with a higher thermal conduc-tivity will result in a smaller uncertainty due to temperaturegradients in this region.7.1.3.3 The walls of the cavity source can be treated inseveral different ways. A painted
40、 or ceramic surface willgenerally result in higher emissivity than an oxidized metalsurface. By the same measure an oxidized metal surface willgenerally result in higher emissivity than a non-oxidized metalsurface. In some cases, it may be impossible to paint the cavitysource surface. This is especi
41、ally true at high temperatures.7.1.3.4 The effective emissivity of the cavity source shall becalculated to determine the radiance temperature of the cavity.Calculation of effective emissivity is beyond the scope of thisstandard. Determination of effective emissivity can be math-ematically calculated
42、 or modeled.7.1.4 Flat-Plate Source:7.1.4.1 A flat-plate source is a device that consists of apainted circular or rectangular plate. The emissivity is likely tobe less well defined than with a cavity source. This can bepartially overcome by performing a radiometric transfer (seeScheme II in 7.3.7) t
43、o the flat-plate source. However, theradiometric transfer should be carried out with an instrumentoperating over a similar spectral band as the infrared thermom-eter under test.7.1.4.2 A cavity source is the preferred radiometric sourcefor infrared thermometer calibrations. The cavity source hastwo
44、main advantages over a flat-plate source. First, the cavitysource has better defined emissivity and an emissivity muchcloser to unity due to its geometric shape. Second, along withFIG. 1 Cavity ShapesE2847 113the emissvity being closer to unity, the effects of reflectedtemperature are lessened. Temp
45、erature uniformity on the flat-plate source may be more of a concern as well. However, aflat-plate source has two possible advantages over a cavitysource. First, the temperature controlled flat-plate surface canbe much larger than a typical cavity source opening, allowingfor much smaller D:S ratios
46、(greater field-of-view). Second, thegeometry of the flat-plate source more likely resembles thesurfaces to be measured by the infrared thermometer under testthan a cavity source.7.2 Aperture:7.2.1 An additional aperture may not be needed for allcalibrations. An aperture is typically used to control
47、scatter. Ifused, the aperture should be temperature-controlled or reflec-tive. An aperture should be used if recommended by theinfrared thermometer manufacturer. If an aperture is used forcalibration, this information should be stated in the report ofcalibration. The information that shall be includ
48、ed is theaperture distance, the aperture size, and the measuring dis-tance.Apossible configuration for aperture use is shown in Fig.2.7.2.2 In Fig. 2,dapris the aperture distance. The measuringdistance is shown by dmeas.7.3 Transfer Standard:7.3.1 The thermal radiation source shall be calibrated wit
49、h atransfer standard traceable to a national metrological institutesuch as the National Institute of Standards and Technology(NIST) or National Research Council (NRC). If a referencethermometer (radiometric or contact) is used during the cali-bration of the unit-under-test, this serves as the calibration ofthe radiation source. In this case, the reference thermometershall have a calibration traceable to a national metrologicalinstitute.7.3.2 This calibration of the thermal radiation source maytake place in the calibration laboratory, or it may be done by athird
