1、Designation: E 1213 97 (Reapproved 2002)Standard Test Method forMinimum Resolvable Temperature Difference for ThermalImaging Systems1This standard is issued under the fixed designation E 1213; 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 resolvable temperature difference (MR
3、TD) capability ofthe compound observer-thermal imaging system as a functionof spatial frequency.1.2 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 p
4、ractices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:E 1316 Terminology for Nondestructive Examinations23. Terminology3.1 Definitions:3.1.1 differential blackbodyan apparatus for establishingtwo parallel isothermal planar zones of
5、 different temperatures,and with effective emissivities of 1.0.3.1.2 See also Terminology E 1316.4. Summary of Test Method4.1 A standard four-bar target is used in conjunction with adifferential blackbody that can establish one blackbody isother-mal temperature for the set of bars and another blackb
6、odyisothermal temperature for the set of conjugate bars, which areformed by the regions between the bars (see Fig. 1). The targetis imaged onto the monochrome video monitor of a thermalimaging system where the image is viewed by an observer. Thetemperature difference between the bars and their conju
7、gates,initially zero, is increased incrementally only until the observercan distinguish the four bars. This critical temperature differ-ence is the MRTD.4.2 The spatial distribution of temperature of each targetmust be measured remotely at the critical temperature differ-ence that determines the MRT
8、D. The mean temperature of eachbar must not differ from that of any other bar by more than themeasured MRTD. A similar requirement applies to the tem-perature of each conjugate bar. Otherwise the MRTD value isunacceptable.4.3 The background temperature and the spatial frequencyof each target must be
9、 specified together with the measuredvalue of MRTD.4.4 The probability of resolution must be specified togetherwith the reported value of MRTD.5. Significance and Use5.1 This test relates to a thermal imaging systems effec-tiveness for discerning details in a scene.5.2 MRTD values provide estimates
10、of resolution capabilityand may be used to compare one system with another. (LowerMRTD values indicate better resolution.)NOTE 1Test values obtained under idealized laboratory conditionsmay or may not correlate directly with service performance.6. Apparatus6.1 The apparatus consists of the following
11、:6.1.1 Test Charts (Targets), comprised of four periodic barsof aspect ratio (width:height) 1:7, as shown in Fig. 1.6.1.2 Differential Blackbody, temporally stable and control-lable to within 0.1C.6.1.3 Infrared Spot Radiometer, calibrated with the aid of ablackbody source to an accuracy within 0.1C
12、.NOTE 2Test charts may be fabricated by cutting slots in metal andcoating with black paint of emissivity greater than 0.95. In this case theslots would constitute the bars.7. Procedure7.1 Mount a test chart (target) onto the differential black-body.NOTE 3Differential blackbodies may be used within a
13、n environmen-tal isothermal temperature chamber. Then, at equilibrium the temperatureof the conjugates approximately equals the temperature of the room, orambient temperature.7.2 Optimally focus the thermal imaging system directly onthe target or on an optical projection of the target.1This test met
14、hod 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 December 10, 1997. Published February, 1998.Originally published as E 1213 87. Last previous edition E 1213 92.2Annual
15、Book of ASTM Standards, Vol 03.03.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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
16、 perceivable by the observer.7.5 Make the display luminance and the laboratory ambientluminance mutually suitable for visual acuity and viewingcomfort.7.6 Instruct the observer to signal when he can perceive theappearance of four distinct bars on the monitor. Refrain fromfurther conversation during
17、the test which could conceivablyinfluence or bias the observer.7.7 Record the distances that determine spatial frequency(see 8.1), and set the nominal DT (the nominal temperature ofthe bars minus the nominal temperature of the conjugate bars,zero or a positive number) equal to zero.7.8 Gradually inc
18、rease the nominal DT in increments notexceeding 0.1C until the observer signals.7.9 Measure the spatial distribution of temperature of thetargets with an infrared spot radiometer of accuracy better than0.1C. Each bar and each conjugate must be measured in atleast three locations that include the end
19、s and centerpoint. Ifadditional locations are measured, all must be at regularintervals. The field of view must be confined to the bar orconjugate being measured.7.10 Calculate the mean temperature of each bar and inter-compare the values, and calculate the mean temperature ofeach conjugate bar and
20、intercompare the values.7.11 Calculate the actual DT (the average temperature of thebars minus the average temperature of the conjugate bars).Provisionally, this is the MRTD.7.12 Compare the largest difference in the mean tempera-tures of any two bars, or any two conjugate bars, with theMRTD. If thi
21、s difference exceeds the MRTD, the test resultsare unacceptable for this particular spatial frequency.7.13 Replace the test chart with another of different spatialfrequency and repeat the test (7.2-7.12).7.14 Repeat 7.13 one or more times.7.15 Repeat the entire test (7.1-7.14) with a different ob-se
22、rver.7.16 Repeat 7.15 one or more times.NOTE 4Observers must be free of eye disease, have good eyesight,and be familiar with viewing thermal imagery.NOTE 5Only one observer at a time shall be present during thetesting.8. Calculation8.1 Calculate the spatial frequency, F, of the test charts asfollows
23、:F 51023DsFcyclesmradG(1)where:F = spatial frequency,D = distance from target to thermal imaging system, m,s = center line to center line separation of bars, m, and D s.8.2 Calculate the probability of resolution as shown by thefollowing illustration: For a given test chart, the MRTD resultsobtained
24、 with three different observers are 0.5C, 0.6C, and1.0C. The observer who resolved 0.5C would also be capableof resolving 0.6C and 1.0C; similarly the observer whoresolved 0.6C would also be capable of resolving 1.0C.Therefore, the respective probabilities of resolution are: for0.5C,13 = 33 %; for 0
25、.6C,23 = 67 %; for 1.0C,33= 100 %.9. Report9.1 Report the following information:9.1.1 Spatial frequency,9.1.2 MRTD,9.1.3 Probability of resolution, and9.1.4 Background temperature.9.2 MRTD values must relate to a probability of resolutionof at least 50 %.9.3 Only a single probability of resolution m
26、ust be usedthroughout.NOTE 6A graph of MRTD versus spatial frequency is a convenientform of reporting the data.FIG. 1 Targets Used for MRTD DeterminationsE 1213 97 (2002)210. Precision and Bias10.1 Insufficient data are available on which to base aprecision and bias statement. Notwithstanding, owing
27、 to thepartially subjective nature of the test, repeatability and repro-ducibility are apt to be poor and MRTD differences less than0.2C are considered to be insignificant.11. Keywords11.1 infrared imaging systems; minimum resolvable tem-perature difference; nondestructive testing; thermal imagingsy
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31、ews known to the ASTM Committee 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 1213 97 (2002)3
