1、Designation: E 1311 89 (Reapproved 2004)Standard Test Method forMinimum Detectable Temperature Difference for ThermalImaging Systems1This standard is issued under the fixed designation E 1311; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、revision, the year 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.1. Scope1.1 This test method covers the determination of the mini-mum detectable temperature difference (MD
3、TD) capability ofa compound observer-thermal imaging system as a function ofthe angle subtended by the target.1.2 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safet
4、y and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 1316 Terminology for Nondestructive Examinations3. Terminology3.1 Definitions:3.1.1 differential blackbodyan apparatus for establishingtwo parallel isothermal p
5、lanar zones of different temperatures,and with effective emissivities of 1.0.3.1.2 field of view (FOV)the shape and angular dimen-sions of the cone or the pyramid that define the object spaceimaged by the system; for example, rectangular, 4-deg wide by3-deg high.3.1.2.1 DiscussionThe size of the fie
6、ld of view is custom-arily expressed in units of degrees.3.1.3 See also Terminology E 1316.4. Summary of Test Method4.1 A standard circular target is used in conjunction with adifferential blackbody that can establish one blackbody isother-mal temperature for the target and another blackbody isother
7、-mal temperature for the background by which the target isframed. The target, at an undisclosed orientation, is imagedonto the monochrome video monitor of a thermal imagingsystem whence the image may be viewed by an observer. Thetemperature difference between the target and the background,initially
8、zero, is increased incrementally until the observer, in alimited duration, can just distinguish the target. This criticaltemperature difference is the MDTD.NOTE 1Observers must have good eyesight and be familiar withviewing thermal imagery.4.2 The temperature distributions of each target and itsback
9、ground are measured remotely at the critical temperaturedifference that defines the MDTD.4.3 The background temperature and the angular subtensefor each target are specified together with the measured valueof MDTD. The (fixed) field of view included by the back-ground is also specified.4.4 The proba
10、bility of detection is specified together withthe reported value of MDTD.5. Significance and Use5.1 This test method gives a measure of a thermal imagingsystems effectiveness for detecting a small spot within a largebackground. Thus, it relates to the detection of small materialdefects such as voids
11、, pits, cracks, inclusions, and occlusions.5.2 MDTD values provide estimates of detection capabilitythat may be used to compare one system with another. (LowerMDTD values indicate better detection capability.)NOTE 2Test values obtained under idealized laboratory conditionsmay or may not correlate di
12、rectly with service performance.6. Apparatus6.1 The apparatus consists of the following:6.1.1 Target Plates, containing single or multiple circulartargets of area(s) not greater than 5 % of the combined areas oftarget and background (that is, FOV area), and with thedistance from the center of the ta
13、rget to the center of the FOVequal to one third of the height or the diameter of the FOV. SeeFig. 1.NOTE 3A target plate may be fabricated by cutting one or morecircular apertures in a metal plate of high thermal conductivity, such asaluminum, and coating with black paint of emissivity greater than
14、0.95. Inthis case an aperture would constitute a target, and the coated metal1This test method is under the jurisdiction of ASTM Committee E07 onNondestructive Testing and is the direct responsibility of Subcommittee E07.10 onEmerging NDT Methods.Current edition approved May 1, 2004. Published June
15、2004. Originallyapproved in 1989. Last previous edition approved in 1999 as E 1311 - 89 (1999).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 Documen
16、t Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.surrounding the target and within the field of view of the thermal imagingsystem would constitute the targets background.6.1.2 Facility, for mounting t
17、arget plates and varying theorientation of any given target through 360.6.1.3 Differential Blackbody, controllable to within 0.1Cand stable over the test period to within 0.1C.6.1.4 Infrared Spot Radiometer, calibrated with the aid of ablackbody source to an uncertainty not exceeding 0.1C.7. Procedu
18、re7.1 Mount a target plate and orient the target in correspon-dence with some integral hour marking on an imaginary clock.Do not divulge the orientation to the observer.NOTE 4Only one observer at a time is to be present during the testing.7.2 Optimally focus the thermal imaging system directly onthe
19、 target or on an optical projection of the target.7.3 Adjust the thermal imaging system for quasi-linearoperation.7.4 Adjust the monochrome video monitor controls so thatthe presence of noise is barely perceivable by the observer.7.5 Make the display luminance and the laboratory ambientluminance mut
20、ually suitable for visual acuity and viewingcomfort.7.6 Advise the observer that a visible spot will eventuallyappear in the monitors display. Instruct him to signal when hecan perceive the spot and to cite its orientation relative to the12 h of a clock; for example, 1 oclock, 2 oclock, 3 oclock,etc
21、. Refrain from further conversation during the test that couldconceivably influence or bias the observer.7.7 Set DT (the temperature of the target minus the nominaltemperature of the background) equal to zero.7.8 Increase DT in positive increments not exceeding 0.1Cevery 60 s or until the observer s
22、ignals. If the identification isincorrect, continue as before.NOTE 5To increase DT it is customary to fix the backgroundtemperature and raise the target temperature.7.9 If the observer correctly identifies the orientation of thespot, record the diameter of the target, the diameter or theheight and w
23、idth of the FOV, and the observation distancenormal to the target plate.7.10 Measure the temperature distribution of the target andthe target background with an infrared spot radiometer replac-ing the thermal imaging system. The target shall be measuredin at least three locations, uniformly spaced.
24、The backgroundshall be measured at two zones: (1) adjacent to the target (thatis, zone 1); (2) beyond zone 1 (that is, zone 2). The measure-ments in each zone shall be uniformly distributed, with thenumber of zone 2 measurements equal to twice that of zone 1(except for the special case of 7.12).7.11
25、 Calculate the mean temperature, T, of the target.Calculate the weighted average, TB, of the target background,in accordance with 8.3. Provisionally, DT=TTBis theMDTD. Record DT and TB.7.12 If the target size and the field of view of the spotradiometer are comparable, make double the number of zone
26、2measurements, in pairs consisting of two adjacent locations.Compare adjacent temperature readings; the difference be-tween any two adjacent readings must be less than the MDTD.Otherwise the MDTD test results are unacceptable for thisparticular target size.NOTE 6This criterion is intended to guard a
27、gainst spurious spots, thatis, false targets.7.13 Replace the target with another of different size.Randomly orient it in accordance with 7.1 and repeat the test(7.2 through 7.12).7.14 Repeat step 7.13 one or more times.7.15 Repeat the entire test (7.1 through 7.14) with a differ-ent observer.7.16 R
28、epeat step 7.15 one or more times.8. Calculations8.1 Calculate the angular subtenses for rectangular FOVs asfollows:uw5 tan21W/R! deg, or (1)5 103W/R mrad;uh5 tan21H/R! deg, or5 103H/R mrad,where:W = width of FOV,R = observation distance normal to centerpoint of FOV,H = height of FOV,R W, andR H.NOT
29、E 7uwmay be referred to as the horizontal field of view, anddenoted HFOV; uhmay be referred to as the vertical field of view, anddenoted VFOV.8.2 Calculate the angular subtenses for circular FOVs andtargets as follows:u5tan21D/R! deg,or (2)FIG. 1 Schematic Showing 1. Target Plate; 2. FOV; and 3. Tar
30、getE 1311 89 (2004)25 103D/R mrad,where:D = diameter of circular FOV or target, as appropriate,R = observation distance normal to centerpoint of FOV orof target, as appropriate, andR D.8.3 Calculate the weighted average, TB, of the target back-ground as follows:TB56(mxi1(nyj6m 1 n(3)where:xi= temper
31、ature measurement in zone 1, i =1,2,.m,yj= temperature measurement in zone 2, j =1,2,.n,m = number of zone 1 temperature measurements,n = number of zone 2 temperature measurements,(mxi= sum of all zone 1 temperature measurements, and(nyj= sum of all zone 2 temperature measurements.NOTE 8Seventy-five
32、 percent of TBis weighted in the vicinity of thetarget.8.4 Calculate the probability of detection as shown by thefollowing illustration:8.4.1 For a given target size, the MDTD results obtainedwith three different observers are 0.5C, 0.6C, 1.0C. Theobserver who detected 0.5C would also be capable of
33、detect-ing 0.6C and 1.0C. Similarly the observer who detected0.6C would also be capable of detecting 1.0C. Hence, therespective probabilities of detection are: for 0.5C,13 =33%;for 0.6C,23 = 67 %; for 1.0C,33 = 100 %.9. Report9.1 Report the following information:9.1.1 Target angular subtense,9.1.2 O
34、bservation distance to target,9.1.3 FOV,9.1.4 MDTD,9.1.5 (Weighted) background temperature, and9.1.6 Probability of detection.9.2 MDTD values should relate to a probability of detectionof at least 50 %.9.3 When comparing different systems, different targets, ordifferent angular subtenses, only a sin
35、gle probability of detec-tion should be used throughout.NOTE 9A plot of MDTD versus target angular subtense is a conve-nient form for reporting the data for a given system or a given target.10. Precision and Bias10.1 PrecisionInsufficient data are available upon whichto formulate a precision stateme
36、nt. Notwithstanding, owing tothe partially subjective nature of the test, repeatability andreproducibility are apt to be poor and MDTD differences lessthan 0.2C are considered to be insignificant.10.2 BiasThe procedure set forth in this test method formeasuring the minimum detectable temperature dif
37、ference forthermal imaging systems has no bias because the minimumdetectable temperature difference can be defined only in termsof a test method.11. Keywords11.1 infrared imaging systems; minimum detectable tem-perature difference; nondestructive testing; thermal imagingsystems; thermography; infrar
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41、ttee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).E 1311 89 (2004)3
