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Sensor: Infrared Thermometer

Sensor: Infrared Thermometer. By David Torgesen. References. [1] Gruner , Klaus-Dieter, “ Principles of Noncontact Temperature Measurement,” http:// support.fluke.com/raytek-sales/Download/Asset/9250315_ENG_A_W.PDF [retrieved 10 March 2010].

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Sensor: Infrared Thermometer

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  1. Sensor:Infrared Thermometer By David Torgesen

  2. References • [1] Gruner, Klaus-Dieter, “Principles of Noncontact Temperature Measurement,” http://support.fluke.com/raytek-sales/Download/Asset/9250315_ENG_A_W.PDF [retrieved 10 March 2010]. • [2] Infrared Thermometer. 2009. Omega Engineering. http://www.omega.com/prodinfo/infraredthermometer.html [retrieved 10 March 2010]

  3. Outline • What is an infrared (IR) thermometer? • What advantages does it have? • What must you keep in mind while using it? • How does it work? • Basic Functionality • Emissivity • How do I measure special materials? • What are the different types of IR thermometers? • Conclusion

  4. What is an IR thermometer? • An IR thermometer is a device that senses the infrared radiation of an object to measure its temperature. http://www.omega.com/prodinfo/infraredthermometer.html

  5. What are the advantages of using an IR thermometer? • There are several advantages to using an IR thermometer: • It measures fast • It can take the measurement of moving objects • It can take the measurement of hazardous or physically inaccessible objects • It can take the measurement of high temperature objects (>1300°C) • No interference (no energy is lost from the object) • No risk of contamination and no mechanical effect on the object’s surface • It can measure the temperature of soft surfaces

  6. What must you keep in mind while using an IR thermometer? • There are certain things to keep in mind while using an IR thermometer: • The object must optically visible to the IR thermometer. High levels of dust and smoke can make the measurement less accurate • The IR sensor must be protected from dust and condensing liquids • Normally, only surface temperatures can be measured

  7. How does an IR thermometer work?Basic Functionality • Every object is made up of molecules. When those molecules are heated up, the intensity of their movement increases. This movement represents charge displacement, and thus, electromagnetic radiation is emitted. Only objects at absolute zero do not emit infrared radiation. http://www.faqs.org/photo-dict/photofiles/list/617/1022molecule.jpg

  8. How does an IR thermometer work? Basic Functionality (Cont.) • The spectrum of this infrared radiation ranges from 0.7 to 1000 μm wavelength. http://support.fluke.com/raytek-sales/Download/Asset/9250315_ENG_A_W.PDF

  9. How does an IR thermometer work? Basic Functionality (Cont.) • This radiation is not visible to the naked eye, but can be seen using an infrared sensor. • The target emits infrared radiation. The detector picks up the energy and converts it into an electrical signal that can be displayed in units of temperature. http://support.fluke.com/raytek-sales/Download/Asset/9250315_ENG_A_W.PDF

  10. How does an IR thermometer work? Emissivity • Emissivity is the ratio of the energy radiated by an object at a given temperature to the energy emitted by a perfect radiator, or blackbody, at the same temperature. • All values of emissivity fall between 0.0 and 1.0. The emissivity of a blackbody is 1.0. • The sum of emission is composed of absorption (A), reflection (R) and transmission (T) is equal to 1.0. http://support.fluke.com/raytek-sales/Download/Asset/9250315_ENG_A_W.PDF

  11. How does an IR thermometer work? Emissivity (Cont.) • Solid bodies have no transmission in the infrared range (T=0). In accordance with Kirchhoff's Law, all the radiation absorbed by a body is then also emitted by this body. • This result gives us A = E = 1 – R. Therefore, the emission is equal to 1 minus the reflection. • For a blackbody, R=0. Therefore, the emission of a blackbody = 1.

  12. How does an IR thermometer work? Emissivity (Cont.) • This chart shows the typical radiation of an ideal blackbody at different temperatures. • Note that the curves do not overlap at different temperatures. • For most applications, the widest wavelength range possible is desired. http://support.fluke.com/raytek-sales/Download/Asset/9250315_ENG_A_W.PDF

  13. How does an IR thermometer work? Emissivity (Cont.) • Sometimes, the widest range possible is not advantageous. • The greater the radiance difference per temperature difference, the more accurately the IR thermometer works. • If you had your IR thermometer set at 2μm, there would be too little energy in objects at temperatures below 850K to get an accurate measurement. • This leads to the idea of an IR thermometer with an adjustable wavelength selection.

  14. How does an IR thermometer work? Emissivity (Cont.) • There are three different types of bodies: • Black body (perfect radiator) • Emissivity = 1 • Gray body (wood, plastic, rubber, organic materials, rock, concrete) • Emissivity between 0.8 and 0.95 • Non-gray body (glass, metals, plastic films) • Emissivity changes with wavelength • The lower the emissivity of the body, the harder it is to measure its temperature.

  15. How does an IR thermometer work? Emissivity (Cont.) • This chart shows the wavelength bodies for different types of bodies. http://support.fluke.com/raytek-sales/Download/Asset/9250315_ENG_A_W.PDF

  16. How do I measure the temperature of special materials? • Metals http://quickshipmetals.com/diamond-plate.gif

  17. How do I measure the temperature of special materials? (Cont.) • Metals (Cont.) • Metals often reflect and therefore have a low emissivity. In this case, you need to select an IR thermometer which measures the infrared radiation at particular wavelength and within a particular temperature range where metals have the highest possible emissivity.

  18. How do I measure the temperature of special materials? (Cont.) • Metals (Cont.) • From the chart, the optimal wavelength for high temperatures is around 0.8 to 1.0 μm. http://support.fluke.com/raytek-sales/Download/Asset/9250315_ENG_A_W.PDF

  19. How do I measure the temperature of special materials? (Cont.) • Plastics http://artblart.files.wordpress.com/2009/08/fpe-fantastic-plastic-elastic-1997-aluminum-and-injection-molded-polypropylene-plastic-sheet.jpg

  20. How do I measure the temperature of special materials? (Cont.) • Plastics (Cont.) • The transmittance of plastic varies with the wavelength and is proportional to its thickness. Thin materials are more transmissive than thick plastics. • It is important to select a wavelength where transmittance is nearly zero. This will vary from material to material. • From the charts at the right, Polyethylene is not transmissive at 3.43 μm while Polyester is not transmissive in the range 7.8 to 8.8μm. http://support.fluke.com/raytek-sales/Download/Asset/9250315_ENG_A_W.PDF

  21. How do I measure the temperature of special materials? (Cont.) • Glass http://www.germes-online.com/direct/dbimage/50332289/Clear_Glass_Vase.jpg

  22. How do I measure the temperature of special materials? (Cont.) • Glass (Cont.) • When measuring the temperature of glass, both reflectance and transmittance must be considered. By carefully selecting the wavelength, it is possible to measure the temperature of the surface as well as the temperature at a depth. • For measurements below the surface, a sensor for 1.0, 2.2, or 3.9 μm wavelength should be used. • For surface measurements, a sensor for 5 μm should be used. • At low temperatures, 8-14 μm should be used. The emissivity should be set to 0.85, which will compensate for reflectance. http://support.fluke.com/raytek-sales/Download/Asset/9250315_ENG_A_W.PDF

  23. What are the different types of IR thermometers? • Handheld • Most popular • Pocket/Stick-Type • Extremely portable • Infrared Thermocouples • Low cost • Self-powered http://www.omega.com/prodinfo/infraredthermometer.html

  24. What are the different types of IR thermometers? (Cont.) • Fixed Mount IR Thermometer/Transmitter • Commonly used in industrial processes • Two Color-Ratio Thermometry • Measures the IR emission at two wavelengths to work practically independent of emissivity http://www.omega.com/prodinfo/infraredthermometer.html

  25. Conclusion • IR Thermometers have several advantages. A few of them are speed, lack of interference, and the ability to measure high temperatures. • While measuring, you must keep in mind the emissivity of the object. Also, IR thermometers mostly measure just the surface temperature of the object.

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