28 Application examples 28.3 Oxidized socket 28.3.1 General Depending on the type of socket and the environment in which the socket is installed, oxides may occur on the socket's contact surfaces. These oxides can lead to locally increased resistance when the socket is loaded, which can be seen in an infrared image as local temperature increase. A socket’s construction may differ dramatically from one manufacturer to another.
8 Application examples 28.4 Insulation deficiencies 28.4.1 General Insulation deficiencies may result from insulation losing volume over the course of time and thereby not entirely filling the cavity in a frame wall. An infrared camera allows you to see these insulation deficiencies because they either have a different heat conduction property than sections with correctly installed insulation, and/or show the area where air is penetrating the frame of the building.
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29 About FLIR Systems FLIR Systems was established in 1978 to pioneer the development of high-performance infrared imaging systems, and is the world leader in the design, manufacture, and marketing of thermal imaging systems for a wide variety of commercial, industrial, and government applications.
29 About FLIR Systems FLIR Systems is at the forefront of innovation in the infrared camera industry. We anticipate market demand by constantly improving our existing cameras and developing new ones. The company has set milestones in product design and development such as the introduction of the first battery-operated portable camera for industrial inspections, and the first uncooled infrared camera, to mention just two innovations. Figure 29.2 1969: Thermovision Model 661.
29 About FLIR Systems 29.3 Supporting our customers FLIR Systems operates a worldwide service network to keep your camera running at all times. If you discover a problem with your camera, local service centers have all the equipment and expertise to solve it within the shortest possible time. Therefore, there is no need to send your camera to the other side of the world or to talk to someone who does not speak your language. #T559880; r.
30 Terms, laws, and definitions Term Definition Absorption and emission2 The capacity or ability of an object to absorb incident radiated energy is always the same as the capacity to emit its own energy as radiation Apparent temperature uncompensated reading from an infrared instrument, containing all radiation incident on the instrument, regardless of its sources3 Color palette assigns different colors to indicate specific levels of apparent temperature.
30 Terms, laws, and definitions Term Definition Radiative heat transfer Heat transfer by the emission and absorption of thermal radiation Reflected apparent temperature apparent temperature of the environment that is reflected by the target into the IR camera13 Spatial resolution ability of an IR camera to resolve small objects or details Temperature measure of the average kinetic energy of the molecules and atoms that make up the substance Thermal energy total kinetic energy of the molecules t
31 Thermographic measurement techniques 31.1 Introduction An infrared camera measures and images the emitted infrared radiation from an object. The fact that radiation is a function of object surface temperature makes it possible for the camera to calculate and display this temperature. However, the radiation measured by the camera does not only depend on the temperature of the object but is also a function of the emissivity. Radiation also originates from the surroundings and is reflected in the object.
31 Thermographic measurement techniques 31.2.1.1.1 Method 1: Direct method Follow this procedure: 1. Look for possible reflection sources, considering that the incident angle = reflection angle (a = b). Figure 31.1 1 = Reflection source 2. If the reflection source is a spot source, modify the source by obstructing it using a piece if cardboard. Figure 31.2 1 = Reflection source #T559880; r.
31 Thermographic measurement techniques 3. Measure the radiation intensity (= apparent temperature) from the reflection source using the following settings: • Emissivity: 1.0 • Dobj: 0 You can measure the radiation intensity using one of the following two methods: Figure 31.3 1 = Reflection source Figure 31.4 1 = Reflection source You can not use a thermocouple to measure reflected apparent temperature, because a thermocouple measures temperature, but apparent temperatrure is radiation intensity. 31.2.
31 Thermographic measurement techniques 5. Measure the apparent temperature of the aluminum foil and write it down. The foil is considered a perfect reflector, so its apparent temperature equals the reflected apparent temperature from the surroundings. Figure 31.5 Measuring the apparent temperature of the aluminum foil. 31.2.1.2 Step 2: Determining the emissivity Follow this procedure: 1. Select a place to put the sample. 2.
31 Thermographic measurement techniques 31.3 Reflected apparent temperature This parameter is used to compensate for the radiation reflected in the object. If the emissivity is low and the object temperature relatively far from that of the reflected it will be important to set and compensate for the reflected apparent temperature correctly. 31.4 Distance The distance is the distance between the object and the front lens of the camera.
32 History of infrared technology Before the year 1800, the existence of the infrared portion of the electromagnetic spectrum wasn't even suspected. The original significance of the infrared spectrum, or simply ‘the infrared’ as it is often called, as a form of heat radiation is perhaps less obvious today than it was at the time of its discovery by Herschel in 1800. Figure 32.1 Sir William Herschel (1738–1822) The discovery was made accidentally during the search for a new optical material.
32 History of infrared technology When Herschel revealed his discovery, he referred to this new portion of the electromagnetic spectrum as the ‘thermometrical spectrum’. The radiation itself he sometimes referred to as ‘dark heat’, or simply ‘the invisible rays’. Ironically, and contrary to popular opinion, it wasn't Herschel who originated the term ‘infrared’. The word only began to appear in print around 75 years later, and it is still unclear who should receive credit as the originator.
32 History of infrared technology Figure 32.4 Samuel P. Langley (1834–1906) The improvement of infrared-detector sensitivity progressed slowly. Another major breakthrough, made by Langley in 1880, was the invention of the bolometer. This consisted of a thin blackened strip of platinum connected in one arm of a Wheatstone bridge circuit upon which the infrared radiation was focused and to which a sensitive galvanometer responded.
33 Theory of thermography 33.1 Introduction The subjects of infrared radiation and the related technique of thermography are still new to many who will use an infrared camera. In this section the theory behind thermography will be given. 33.2 The electromagnetic spectrum The electromagnetic spectrum is divided arbitrarily into a number of wavelength regions, called bands, distinguished by the methods used to produce and detect the radiation.
33 Theory of thermography Figure 33.2 Gustav Robert Kirchhoff (1824–1887) The construction of a blackbody source is, in principle, very simple. The radiation characteristics of an aperture in an isotherm cavity made of an opaque absorbing material represents almost exactly the properties of a blackbody. A practical application of the principle to the construction of a perfect absorber of radiation consists of a box that is light tight except for an aperture in one of the sides.
33 Theory of thermography where: Wλb Blackbody spectral radiant emittance at wavelength λ. c Velocity of light = 3 × 108 m/s h Planck’s constant = 6.6 × 10-34 Joule sec. k Boltzmann’s constant = 1.4 × 10-23 Joule/K. T Absolute temperature (K) of a blackbody. λ Wavelength (μm). Note The factor 10-6 is used since spectral emittance in the curves is expressed in Watt/m2, μm. Planck’s formula, when plotted graphically for various temperatures, produces a family of curves.
33 Theory of thermography Figure 33.5 Wilhelm Wien (1864–1928) The sun (approx. 6 000 K) emits yellow light, peaking at about 0.5 μm in the middle of the visible light spectrum. At room temperature (300 K) the peak of radiant emittance lies at 9.7 μm, in the far infrared, while at the temperature of liquid nitrogen (77 K) the maximum of the almost insignificant amount of radiant emittance occurs at 38 μm, in the extreme infrared wavelengths. Figure 33.
33 Theory of thermography Figure 33.7 Josef Stefan (1835–1893), and Ludwig Boltzmann (1844–1906) Using the Stefan-Boltzmann formula to calculate the power radiated by the human body, at a temperature of 300 K and an external surface area of approx. 2 m2, we obtain 1 kW.
33 Theory of thermography • A selective radiator, for which ε varies with wavelength According to Kirchhoff’s law, for any material the spectral emissivity and spectral absorptance of a body are equal at any specified temperature and wavelength. That is: From this we obtain, for an opaque material (since αλ + ρλ = 1): For highly polished materials ελ approaches zero, so that for a perfectly reflecting material (i.e.
33 Theory of thermography 33.4 Infrared semi-transparent materials Consider now a non-metallic, semi-transparent body – let us say, in the form of a thick flat plate of plastic material. When the plate is heated, radiation generated within its volume must work its way toward the surfaces through the material in which it is partially absorbed. Moreover, when it arrives at the surface, some of it is reflected back into the interior.
34 The measurement formula As already mentioned, when viewing an object, the camera receives radiation not only from the object itself. It also collects radiation from the surroundings reflected via the object surface. Both these radiation contributions become attenuated to some extent by the atmosphere in the measurement path. To this comes a third radiation contribution from the atmosphere itself.
34 The measurement formula 2. Reflected emission from ambient sources = (1 – ε)τWrefl, where (1 – ε) is the reflectance of the object. The ambient sources have the temperature Trefl. It has here been assumed that the temperature Trefl is the same for all emitting surfaces within the halfsphere seen from a point on the object surface. This is of course sometimes a simplification of the true situation.
34 The measurement formula magnitudes of the three radiation terms. This will give indications about when it is important to use correct values of which parameters. The figures below illustrates the relative magnitudes of the three radiation contributions for three different object temperatures, two emittances, and two spectral ranges: SW and LW. Remaining parameters have the following fixed values: • τ = 0.
34 The measurement formula Figure 34.3 Relative magnitudes of radiation sources under varying measurement conditions (LW camera). 1: Object temperature; 2: Emittance; Obj: Object radiation; Refl: Reflected radiation; Atm: atmosphere radiation. Fixed parameters: τ = 0.88; Trefl = 20°C (+68°F); Tatm = 20°C (+68°F). #T559880; r.
35 Emissivity tables This section presents a compilation of emissivity data from the infrared literature and measurements made by FLIR Systems. 35.1 References 1. Mikaél A. Bramson: Infrared Radiation, A Handbook for Applications, Plenum press, N.Y. 2. William L. Wolfe, George J. Zissis: The Infrared Handbook, Office of Naval Research, Department of Navy, Washington, D.C. 3. Madding, R. P.: Thermographic Instruments and systems.
35 Emissivity tables Table 35.1 T: Total spectrum; SW: 2–5 µm; LW: 8–14 µm, LLW: 6.5–20 µm; 1: Material; 2: Specification; 3:Temperature in °C; 4: Spectrum; 5: Emissivity: 6:Reference (continued) 1 2 3 4 5 6 Aluminum anodized, light gray, dull 70 SW 0.61 9 Aluminum anodized, light gray, dull 70 LW 0.97 9 Aluminum as received, plate 100 T 0.09 4 Aluminum as received, sheet 100 T 0.09 2 Aluminum cast, blast cleaned 70 SW 0.47 9 Aluminum cast, blast cleaned 70 LW 0.
35 Emissivity tables Table 35.1 T: Total spectrum; SW: 2–5 µm; LW: 8–14 µm, LLW: 6.5–20 µm; 1: Material; 2: Specification; 3:Temperature in °C; 4: Spectrum; 5: Emissivity: 6:Reference (continued) 1 2 3 4 5 6 Brass oxidized 70 LW 0.03–0.07 9 Brass oxidized at 600°C 200–600 T 0.59–0.61 1 Brass polished 200 T 0.03 1 Brass polished, highly 100 T 0.03 2 Brass rubbed with 80grit emery 20 T 0.20 2 Brass sheet, rolled 20 T 0.06 1 Brass sheet, worked with emery 20 T 0.
35 Emissivity tables Table 35.1 T: Total spectrum; SW: 2–5 µm; LW: 8–14 µm, LLW: 6.5–20 µm; 1: Material; 2: Specification; 3:Temperature in °C; 4: Spectrum; 5: Emissivity: 6:Reference (continued) 1 2 3 4 5 6 Carbon graphite, filed surface 20 T 0.98 2 Carbon lampblack 20–400 T 0.95–0.97 1 Chipboard untreated 20 SW 0.90 6 Chromium polished 50 T 0.10 1 Chromium polished 500–1000 T 0.28–0.38 1 Clay fired 70 T 0.91 1 Cloth black 20 T 0.98 1 20 T 0.
35 Emissivity tables Table 35.1 T: Total spectrum; SW: 2–5 µm; LW: 8–14 µm, LLW: 6.5–20 µm; 1: Material; 2: Specification; 3:Temperature in °C; 4: Spectrum; 5: Emissivity: 6:Reference (continued) 1 2 3 4 5 6 Glass pane (float glass) non-coated 20 LW 0.97 14 Gold polished 130 T 0.018 1 Gold polished, carefully 200–600 T 0.02–0.03 1 Gold polished, highly 100 T 0.02 2 Granite polished 20 LLW 0.849 8 Granite rough 21 LLW 0.
35 Emissivity tables Table 35.1 T: Total spectrum; SW: 2–5 µm; LW: 8–14 µm, LLW: 6.5–20 µm; 1: Material; 2: Specification; 3:Temperature in °C; 4: Spectrum; 5: Emissivity: 6:Reference (continued) 1 2 3 4 5 6 Iron and steel rusty, red 20 T 0.69 1 Iron and steel shiny oxide layer, sheet, 20 T 0.82 1 Iron and steel shiny, etched 150 T 0.16 1 Iron and steel wrought, carefully polished 40–250 T 0.28 1 Iron galvanized heavily oxidized 70 SW 0.
35 Emissivity tables Table 35.1 T: Total spectrum; SW: 2–5 µm; LW: 8–14 µm, LLW: 6.5–20 µm; 1: Material; 2: Specification; 3:Temperature in °C; 4: Spectrum; 5: Emissivity: 6:Reference (continued) 1 2 3 4 5 6 Lead oxidized, gray 22 T 0.28 4 Lead shiny 250 T 0.08 1 Lead unoxidized, polished 100 T 0.05 4 100 T 0.93 4 100 T 0.93 1 T 0.75–0.80 1 Lead red Lead red, powder Leather tanned Lime T 0.3–0.4 1 Magnesium 22 T 0.07 4 Magnesium 260 T 0.13 4 538 T 0.
Emissivity tables Table 35.1 T: Total spectrum; SW: 2–5 µm; LW: 8–14 µm, LLW: 6.5–20 µm; 1: Material; 2: Specification; 3:Temperature in °C; 4: Spectrum; 5: Emissivity: 6:Reference (continued) 1 2 3 4 5 6 Nickel oxidized at 600°C 200–600 T 0.37–0.48 1 Nickel polished 122 T 0.045 4 Nickel wire 200–1000 T 0.1–0.2 1 1000–1250 T 0.75–0.86 1 Nickel oxide Nickel oxide 500–650 T 0.52–0.59 1 Oil, lubricating 0.025 mm film 20 T 0.27 2 Oil, lubricating 0.
35 Emissivity tables Table 35.1 T: Total spectrum; SW: 2–5 µm; LW: 8–14 µm, LLW: 6.5–20 µm; 1: Material; 2: Specification; 3:Temperature in °C; 4: Spectrum; 5: Emissivity: 6:Reference (continued) 1 2 3 4 5 6 Paper white, 3 different glosses 70 LW 0.88–0.90 9 Paper yellow T 0.72 1 17 SW 0.86 5 Plaster plasterboard, untreated 20 SW 0.90 6 Plaster rough coat 20 T 0.91 2 Plastic glass fibre laminate (printed circ. board) 70 SW 0.
35 Emissivity tables Table 35.1 T: Total spectrum; SW: 2–5 µm; LW: 8–14 µm, LLW: 6.5–20 µm; 1: Material; 2: Specification; 3:Temperature in °C; 4: Spectrum; 5: Emissivity: 6:Reference (continued) 1 2 3 4 5 6 Slag boiler 600–1200 T 0.76–0.70 1 Soil dry 20 T 0.92 2 Soil saturated with water 20 T 0.95 2 Stainless steel alloy, 8% Ni, 18% Cr 500 T 0.35 1 Stainless steel rolled 700 T 0.45 1 Stainless steel sandblasted 700 T 0.
35 Emissivity tables Table 35.1 T: Total spectrum; SW: 2–5 µm; LW: 8–14 µm, LLW: 6.5–20 µm; 1: Material; 2: Specification; 3:Temperature in °C; 4: Spectrum; 5: Emissivity: 6:Reference (continued) 1 2 3 4 5 6 Water frost crystals –10 T 0.98 2 Water ice, covered with heavy frost 0 T 0.98 1 Water ice, smooth 0 T 0.97 1 Water ice, smooth –10 T 0.96 2 Water layer >0.1 mm thick 0–100 T 0.95–0.98 1 Water snow T 0.8 1 Water snow –10 T 0.85 2 Wood 17 SW 0.
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