1. A Study on the Effects of Bandwidth of IR Thermometry Measurements Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 1 NCSL International 2009

2. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 2 Overview Introduction Bandwidth in Wideband Instruments Blackbody Emissivity The Mathematical Challenge The Mathematical Solution Practical Experimentation Conclusion

3. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 3 Overview Introduction Bandwidth in Wideband Instruments Blackbody Emissivity The Mathematical Challenge The Mathematical Solution Practical Experimentation Conclusion

4. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 4 Introduction Calculating an uncertainty budget - every factor should be considered Uncertainty in bandwidth combined with emissivity variation –Complex problem –The actual bandwidth or spectral response of the IR thermometer may not be known –Difficulty with mathematics

5. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 5 Overview Introduction Bandwidth in Wideband Instruments Blackbody Emissivity The Mathematical Challenge The Mathematical Solution Practical Experimentation Conclusion

6. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 6 Bandwidth in Wideband Instruments Make and ModelBandwidth Craftsman 504666 – 14 µm Extec 425456 – 14 µm Fluke 626.5 – 18 µm Fluke 668 – 14 µm Fluke 5728 – 14 µm Metris TL400L5 – 14 µm Omega OSXL4507 – 18 µm Omega OS5308 – 14 µm Omega OSXL6505 – 14 µm Omega OSXL6808 – 14 µm TPI 3817 – 14 µm ZY Temp TN400L5 – 14 µm ZY Temp TN423LCE8 – 14 µm

7. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 7 Testing for Bandwidth Testing is possible SCIRCUS at NIST in Gaithersburg, MD Cost

8. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 8 Wideband IR Thermometers An IR thermometer’s spectral response may not be practical to determine Just determining bandwidth may not be practical A few assumptions may be made –A measurement of the surface’s emissivity –Assuming the bandwidth variation to be an arbitrary number Testing for the validity of these assumptions was tested

9. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 9 Overview Introduction Bandwidth in Wideband Instruments Blackbody Emissivity The Mathematical Challenge The Mathematical Solution Practical Experimentation Conclusion

10. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 10 Blackbody Emissivity Blackbody = an ideal thermal radiator Emissivity of unity Not achievable Geometric shapes come close (cavity) Cavities are good for calibrations –Not encountered in practical measurements

11. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 11 Non Blackbody Surfaces Flat surfaces do not act as blackbodies –ε < 1.00 Gray body has constant emissivity regardless of wavelength –ε(λ) = K

12. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 12 Emissivity’s Dependence on Wavelength

13. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 13 Overview Introduction Bandwidth in Wideband Instruments Blackbody Emissivity The Mathematical Challenge The Mathematical Solution Practical Experimentation Conclusion

14. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 14 The Mathematical Challenge Emissivity not constant with wavelength Calculating the effects of bandwidth uncertainty –Total power density emitted over the IR thermometer’s bandwidth S(λ) –Spectral response of emissivity (ε(λ))

15. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 15 Planckian Model

16. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 16 Challenges Faced with Integrating Planck’s Law

17. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 17 Overview Introduction Bandwidth in Wideband Instruments Blackbody Emissivity The Mathematical Challenge The Mathematical Solution Practical Experimentation Conclusion

18. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 18 Averaging Emissivity Simple Average

19. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 19 Averaging Emissivity Half-band

20. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 20 Theoretical Comparison of Laws

21. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 21 Theoretical Comparison of Laws

22. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 22 Overview Introduction Bandwidth in Wideband Instruments Blackbody Emissivity The Mathematical Challenge The Mathematical Solution Practical Experimentation Conclusion

23. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 23 Setup Several flat plate IR calibrators measured –Painted with Paint 1 and Paint 2 Baseline taken with high-end 8-14µm IR thermometer –4 temperatures (100°C, 200°C, 350°C, 500°C) A number of handheld IR thermometers were used to make measurements Differences in temperature readout were noted

24. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 24 Uncertainties UncertaintyType IR Thermometer Measurement A Radiometer Measurement A Target DriftA FTIR DataB

25. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 25 Uncertainties IRT 1&2IRT 3&4IRT 5, 6 &7 IRT 8 U (°C) U (°C) U (°C) U (°C) 100°C0.3810.3080.3380.298 200°C0.4000.3870.5700.621 350°C0.5681.0241.2111.167 500°C1.1111.7702.4631.808

26. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 26 Theoretical Values T8-14µm Δε 7-14µm Δε 5-20µm Δε 100°C+0.006-0.002-0.011 200°C+0.006-0.004-0.019 350°C+0.006-0.006-0.022 500°C+0.006-0.007-0.034

27. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 27 Results

28. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 28 Results

29. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 29 Discussion 8-14µm –Mostly within the experimental uncertainties –Within the theoretical differences –∆ε = 1 µm is valid –This uncertainty is not significant compared to the overall uncertainty 5-20µm –close to theory –additional bandwidth variance

30. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 30 Overview Introduction Bandwidth in Wideband Instruments Blackbody Emissivity The Mathematical Challenge The Mathematical Solution Practical Experimentation Conclusion

31. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 31 Conclusion Simple average OK for small differences in bandwidth (spectral response) Considering a 1 µm variance is valid assumption when comparing 8-14 µm instruments Great care must be taken when using 5-20 µm instruments

32. Frank Liebmann NCSLi 2009 © 2008 Fluke Corporation 32 Questions ?