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| [[Image:Gluehfadenpyrometer.jpg|thumb|upright|An optical pyrometer]]
| | My name is Sheldon and I am studying Chemistry and Agriculture and Life Sciences at Montmorency / Australia.<br><br>Feel free to visit my blog post - [http://grooveshark.com/#!/profile/Arthur+Falcone+Stargazer/23992863 Arthur Falcone] |
| [[Image:Pyrometer 040824.jpg|thumb|upright|A sailor checking the temperature of a ventilation system]]
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| A '''pyrometer''' is a type of thermometer used to measure high temperatures. Various forms of pyrometers have historically existed. In the modern usage, it is a non-contacting device that intercepts and measures [[thermal radiation]], a process known as pyrometry. The thermal radiation can be used to determine the [[temperature]] of an object's surface.
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| The word pyrometer comes from the [[Greek language|Greek]] word for fire, "πυρ" (''pyro''), and ''meter'', meaning to measure. Pyrometer was originally coined to denote a device capable of measuring temperatures of objects above [[incandescence]] (i.e. objects bright to the human eye).{{Citation needed|date=August 2013}}
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| == Principle of operation ==
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| A modern pyrometer has an optical system and a detector. The optical system focuses the [[thermal radiation]] onto the detector. The output signal of the detector (temperature ''T'') is related to the [[thermal radiation]] or [[irradiance]] ''j''<sup>*</sup> of the target object through the [[Stefan–Boltzmann law]], the [[constant of proportionality]] σ, called the [[Stefan-Boltzmann constant]] and the [[emissivity]] ε of the object.
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| :<math>
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| j^{\star} = \varepsilon\sigma T^{4}
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| </math>
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| This output is used to infer the object's temperature. Thus, there is no need for direct contact between the pyrometer and the object, as there is with [[thermocouple]]s and [[resistance temperature detector]]s (RTDs).
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| ==History==
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| The potter [[Josiah Wedgwood]] invented the first pyrometer to measure the temperature in his kilns,<ref>{{cite web|url=http://www.bbc.co.uk/history/historic_figures/wedgwood_josiah.shtml |title=History - Historic Figures: Josiah Wedgwood (1730 - 1795) |publisher=BBC |date=1970-01-01 |accessdate=2013-08-31}}</ref> which first compared the color of clay fired at known temperatures, but was eventually upgraded to measuring the shrinkage of pieces of clay, which depended on the heat of the kiln.<ref>{{cite web|url=http://www.wedgwoodmuseum.org.uk/learning/discovery-packs/pack/lives-of-the-wedgwoods/chapter/pyrometer|title=Pyrometer |publisher=Wedgwood Museum |accessdate=23 August 2013}}</ref> Later examples used the expansion of a metal bar.<ref>{{cite book |last=Draper |first=John William |title=A Textbook on chemistry |year=1861 |publisher=Harper & Bros|page=24 |url=http://books.google.co.uk/books?id=HKwS7QDh5eMC&pg=PA1&dq=draper,+john+william&source=gbs_toc_r&cad=4#v=onepage&q&f=false }}</ref> [[File:Pyrometer example.png|thumb|A pyrometer from 1852. Heating the metal bar (a) presses against a lever (b), which presses against another lever (c) that serves as a measuring index. (e) is an immovable prop which holds the bar in place. A spring on (c) pushes against (b), causing the index to fall back once the bar cools.]]
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| Modern pyrometers became available when the first [[disappearing filament pyrometer]] was built by L. Holborn and F. Kurlbaum in 1901.<ref name=Michalski>L. Michalski et al, ''Temperature Measurement, Second Edition''. (Wiley, 2001), pp. 162–208.</ref> This device superimposed a thin, heated filament over the object to be measured and relied on the operator’s eye to detect when the filament vanished.<ref name=Mercer>C. Mercer, ''Optical metrology for fluids, combustion, and solids''. (Kluwer Academic, 2003), pp. 297–305.</ref> The object temperature was then read from a scale on the pyrometer.
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| The temperature returned by the vanishing filament pyrometer and others of its kind, called brightness pyrometers, is dependent on the emissivity of the object. With greater use of brightness pyrometers, it became obvious that problems existed with relying on knowledge of the value of emissivity. Emissivity was found to change, often drastically, with surface roughness, bulk and surface composition, and even the temperature itself.<ref name=Ng>{{cite journal|author=D. Ng and G. Fralick |url=http://rsi.aip.org/rsinak/v72/i2/p1522_s1 |title=Use of a multiwavelength pyrometer in several elevated temperature aerospace applications |journal=Review Scientific Instruments |volume=72 |issue=2 |page=1522 |year=2001 |doi=10.1063/1.1340558 }}</ref>
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| To get around these difficulties, the ratio or two-color pyrometer was developed. They rely on the fact that [[Planck's law]], which relates temperature to the intensity of radiation emitted at individual wavelengths, can be solved for temperature if Planck’s statement of the intensities at two different wavelengths is divided. This solution assumes that the emissivity is the same at both wavelengths <ref name=Mercer/> and cancels out in the division. This is known as the [[emissivity#Explanation|gray body assumption]]. Ratio pyrometers are essentially two brightness pyrometers in a single instrument. The operational principles of the ratio pyrometers were developed in the 1920s and 1930s, and they were commercially available in 1939.<ref name=Michalski/>
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| As the ratio pyrometer came into popular use, it was determined that many materials, of which metals are an example, do not have the same emissivity at two wavelengths.<ref name = Olinger>{{cite web|url=http://www.docstoc.com/docs/22165998/Successful-Pyrometry-in-Investment-Casting |author=D. Olinger, J. Gray, R. Felice|chapter=Successful Pyrometry in Investment Casting| title=Proceedings of the 55th Annual Technical Conference on Investment Casting |publisher=Investment Casting Institute|year= 2007 |via=Docstoc.com |date=2010-01-13 |accessdate=2013-08-31}}</ref> For these materials, the emissivity does not cancel out and the temperature measurement is in error. The amount of error depends on the emissivities and the wavelengths where the measurements are taken.<ref name=Mercer/> Two-color ratio pyrometers cannot measure whether a material’s emissivity is wavelength dependent.
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| To more accurately measure the temperature of real objects with unknown or changing emissivities, multiwavelength pyrometers were envisioned at the US [[National Institute of Standards and Technology]] and described in 1992.<ref name=Michalski/> Multiwavelength pyrometers use three or more wavelengths and mathematical manipulation of the results to attempt to achieve accurate temperature measurement even when the emissivity is unknown, changing, and different at all wavelengths.<ref name=Mercer/><ref name=Ng/><ref name = Olinger/>
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| == Applications ==
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| Pyrometers are suited especially to the measurement of moving objects or any surfaces that can not be reached or can not be touched.
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| === Smelter Industry ===
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| Temperature is a fundamental parameter in [[metallurgy|metallurgical]] [[furnace]] operations. Reliable and continuous measurement of the melt temperature is essential for effective control of the operation. Smelting rates can be maximized, [[slag]] can be produced at the optimum temperature, fuel consumption is minimized and refractory life may also be lengthened. [[Thermocouple]]s were the traditional devices used for this purpose, but they are unsuitable for continuous measurement because they melt and degrade.
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| === Over-the-bath Pyrometer ===
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| [[Ferritic nitrocarburizing|Salt bath]] furnaces operate at temperatures up to 1300 °C and are used for [[heat treatment]]. At very high working temperatures with intense heat transfer between the molten salt and the steel being treated, precision is maintained by measuring the temperature of the molten salt. Most errors are caused by [[slag]] on the surface which is cooler than the salt bath.<ref>L. Michalski et al, “Temperature Measurement, Second Edition''.(Wiley, 2001), pp. 403-404.</ref>
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| === Tuyère Pyrometer ===
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| The Tuyère Pyrometer is an optical instrument for temperature measurement through the [[tuyere]]s which are normally used for feeding air or reactants into the bath of the furnace.
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| [[Image:Smelter-pyrometer.png|thumb|center|512px|(1) Display.(2) Optical.(3) Fibre optic cable and Periscope. (4) Pyrometer tuyère adapter having:i. Bustle pipe connection. ii. Tuyère clamp iii. Clamp washer iv. Clamp stud c/w and fastening hardware
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| v. Gasket
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| vi. Noranda Tuyère Silencer
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| vii. valve seat
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| viii. ball
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| (5) Pneumatic Cylinder:
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| i. Smart Cylinder Assembly with Internal proximity switch
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| ii. Guard Plate Assembly
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| iii. Temporary Flange Cover Plate used to cover periscope entry hole on tuyère adapter when no cylinder is installed on the tuyère.
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| (6) Operator station panel
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| (7) Pyrometer light station
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| (8) Limit switches
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| (9) 4 conductor cab tire
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| (10) Ball Valve
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| (11) Periscope Air pressure switch.
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| (12) Bustle Pipe Air pressure switch.
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| (13) Airline filter/regulator
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| (14) Directional control valve, Sub-plate, silencer and speed control mufflers.
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| (15) 2" nom. low pressure air hose, 40m length]]
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| ===Steam boilers===
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| A steam [[boiler]] may be fitted with a pyrometer to measure the steam temperature in the [[superheater]].
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| ===Hot Air Balloons===
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| A [[hot air balloon]] is equipped with a pyrometer for measuring the temperature at the top of the envelope in order to prevent overheating of the fabric.
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| ==Pyrometry of gases==
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| Pyrometry of gases presents difficulties. These are most commonly overcome by using [[thin filament pyrometry]] or [[soot]] pyrometry. Both techniques involve small solids in contact with hot gases.
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| == See also ==
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| * [[Aethrioscope]]
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| * [[Infrared thermometer]]
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| * [[Tasimeter]]
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| * [[Thermal radiation]]
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| * [[Thin filament pyrometry]]
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| * [[Thermography]]
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| == References ==
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| {{reflist}}
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| == External links ==
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| {{commons category|Pyrometers}}
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| *[http://www.freepatentsonline.com/4619533.html The tuyère pyrometer patent]
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| *[http://www.omega.com/literature/transactions/volume1/thermometers1.html Infrared and radiation pyrometers]
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| *[http://www.freepatentsonline.com/5772323.html A multiwavelength pyrometer patent]
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| [[Category:Radiometry]]
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| [[Category:Thermometers]]
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| [[Category:Combustion]]
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| [[Category:Measuring instruments]]
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| [[Category:Metallurgical processes]]
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| [[Category:Infrared imaging]]
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| [[ar:مقياس الإشعاع الحراري]]
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My name is Sheldon and I am studying Chemistry and Agriculture and Life Sciences at Montmorency / Australia.
Feel free to visit my blog post - Arthur Falcone