Understanding Infrared Thermography Reading 7 Part 2 of 2.pdf

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Emissivity is a cantankerous 脾气坏且抱怨不休的 variable As we’ve seen, emissivity varies by surface condition, but also by viewing angle, and even by temperature and by spectral wavelength. A table of common emissivity values is published in the operating manual for your thermal imager. The table should be considered only a rough guide in estimating an emissivity value to use with any particular material. If actual temperature values are required, it is best to perform experiments as described here, to properly characterize the emissivity for the material and its application. The two most common techniques for providing a higher emissivity reference surface are the application of a flat black high emissivity paint to the surface (as discussed in the previous section), or application of common black electrical tape to the material’s surface. Both black electrical tape and flat black tape have an emissivity of approximately 0.96. Another option is to use an infrared thermometer with adjustable emissivity, and a contact probe, adjusting the emissivity until the contact probe and infrared temperature displays equilibrate. Charlie Chong/ Fion Zhang http://reliableplant.com/Read/14134/emissivity-underst-difference-between-apparent,-actual-ir-temps
In this experiment we see that the difference between the apparent temperature on the unpainted side and actual temperature is an error of 106 ºF. If we were to conduct a similar experiment with a high-temperature infrared sensor, and examine steel at 2,000 ºF, the error between the actual and apparent temperatures could be more than 400 ºF. Of course, neither black paint or tape could survive 2,000 ºF. It’s often useful to use a narrow spectral band similar to the wavelength of the object’s radiant energy. Wien’s displacement law helps us determine the peak wavelength of the object’s peak radiant energy for an object at a certain temperature. λ max = b / T where: λ max = peak wavelength of radiant energy b = 2897 μm/ °K T = temperature (Kelvin) Charlie Chong/ Fion Zhang http://reliableplant.com/Read/14134/emissivity-underst-difference-between-apparent,-actual-ir-temps
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Infrared Thermal Testing Reading VI
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6.1 Basic Elements An in-house prog
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6.1.4 Responsibilities This section
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IR Viewing Window - Opaque Polymer
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6.1.8 Acceptance Criteria All surve
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6.1.9 Reporting Criteria A rigid pr
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6.1.10 Qualification of Personnel P
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EPRI Licensed Material Basic Elemen
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7. TRAINING AND CERTIFICATION This
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Recommended training and certificat
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■ Level II A Level II infrared th
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The experience and education recomm
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B. Spatial Resolution • the conce
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D. Equipment Operation • Be able
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The PdM basic examination is more s
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Appendix-A The Science Of Thermogra
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Erroneous conclusions can have an e
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A.2.1 Heat and Temperature What is
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To convert changes in temperature o
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A.2.3 The Three Modes of Heat Trans
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The Fourier Conduction Law: Q/A Q =
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A.2.5 Convection Convective heat tr
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Figure A-2 Convective Heat Flow Cha
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A.2.6 Radiation Radiative heat tran
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A.2.7 Radiation Exchange at the Tar
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Charlie Chong/ Fion Zhang
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Figure A-4 Radiative Heat Flow W ε
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A.2.8 Specular and Diffuse Surfaces
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Specular or Diffuse Surfaces Diffus
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Specular and Diffuse Surfaces Confu
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Specular reflection is the mirror-l
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Reflections off Specular and Diffus
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The thermogram of the outside surfa
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Steady-state conduction Steady stat
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A.3 The Basic Physics of Infrared R
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A.3.1 Some Historical Background Th
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A.3.3 The Target Surface The chart
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Figure A-6 shows the distribution o
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Two physical laws define the radian
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According to (2), the wavelength at
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Figure A-7 Spectral Distribution of
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Figure A-8 shows that the instrumen
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If the emissivity of a gray body is
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Under certain conditions, an error
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EXAM score! Non-graybody (colored b
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Figure A-10 illustrates the spectra
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Figure A-10 Infrared Transmission o
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Figure A-11 Infrared Spectral Trans
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Figure A-11 shows transmission curv
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EXAM score! Glass is opaque λ > 5
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Figure A-12 Characteristics of IR T
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The characteristics of the window m
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IR Lenses - LWIR Len Charlie Chong/
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IR Lenses - Fresnel Len Charlie Cho
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Figure A-13 Components of an Infrar
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Infrared optics are available in tw
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All infrared detector-transducers e
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Figure A-14 Typical Infrared Radiat
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Germanium Len Charlie Chong/ Fion Z
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Thermopile Detector Charlie Chong/
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The IR Detectors Infrared detectors
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Figure A-15 Spectral Sensitivity of
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The Mercury- Cadmium-telluride (Hgc
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The Mercury- Cadmium-Telluride (HgC
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Point-sensing instruments for measu
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A.3.6.1 Line Scanning The purpose o
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A.3.6.2 Two-Dimensional Scanning Th
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Opto-mechanical Scanner A typical c
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Electronic scanning Electronic scan
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Figure A-18 Schematic of a Typical
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Applications for infrared FPAs incl
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Staring Charlie Chong/ Fion Zhang
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A.4.1 Point-Sensing Instruments For
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Temperature sensitivity is also cal
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EXAM score! thermal resolution (≠
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NETD - Noise Equivalent Temperature
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Figure A-19 Instrument Speed of Res
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Figure A-20 Fields of View of Infra
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Figure A-20 Fields of View of Infra
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The output requirements are totally
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Spectrally selective instruments em
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Figure A-21 Spectral Filtering for
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Figure A-22 shows a similar solutio
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A.4.2 Scanners and Imagers.Qualitat
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• Total field of view (TFOV): the
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Despite some manufacturers’ claim
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A.4.3.1 Temperature Sensitivity, Mi
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Figure A-23 Test Setup for MRTD Mea
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A.4.3.2 Spot Size (FOV) , Instantan
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■ A standard 4 bar (slit) resolut
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Both MRTD and MTF are functions of
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IFOVmeas: The slit width at which t
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FPA Charlie Chong/ Fion Zhang http:
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FPA Charlie Chong/ Fion Zhang
Page 215 and 216: A.4.3.3 Speed of Response and Frame
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Page 219 and 220: The newest field-portable instrumen
Page 221 and 222: Appendix B Measuring Emissivity, Re
Page 223 and 224: Figure B-1 Target Radiosity Charlie
Page 225 and 226: The reference emitter technique wor
Page 227 and 228: 1. Apply the reference emitter (E)
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Page 231 and 232: Figure B-3 Using the Reflective Emi
Page 233 and 234: Figure B-4 Using the Transmittance
Page 235 and 236: Appendix C Quick Reference Charts A
Page 237 and 238: MTF Determination Using An Ir Image
Page 239 and 240: Measuring And Setting Effective Emi
Page 241 and 242: Classification Of Faults (Guideline
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Page 245 and 246: Reading: Four Emissivity: Understan
Page 247 and 248: Figure 1 shows a typical three-phas
Page 249 and 250: Figure IR1: Corresponding infrared
Page 251 and 252: Thermal radiation and properties of
Page 253 and 254: The thermal nature of materials. Ma
Page 255 and 256: So in plain English, when the therm
Page 257 and 258: Figure 2: Stainless steel block. (a
Page 259 and 260: Observed with our thermal imager (w
Page 261 and 262: Can you see my eye glasses in the i
Page 263 and 264: How can the thermal imager’s read
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Page 271 and 272: Using a narrow band filter to measu
Page 273 and 274: Emissivity, the variable’s variab
Page 275 and 276: Emissivity and electrical equipment
Page 277 and 278: In manufacturing processes, steel o
Page 279 and 280: In this case, we have another power
Page 281 and 282: Figure IR1: Corresponding infrared
Page 283 and 284: Figure 7: Measuring the loads on a
Page 285 and 286: Summary Predictive maintenance PDM
Page 287 and 288: It is much like most endeavors in l
Page 289 and 290: Good Luck Charlie Chong/ Fion Zhang
Page 291: Charlie https://www.yumpu.com/en/br
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