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Merjenje vpliva velikosti tarče pri termovizijski kameri
KODRIČ, SLAVKO (Author), Pušnik, Igor (Mentor) More about this mentor... This link opens in a new window

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Abstract
Za brezkontaktno merjenje temperature, ki se uporablja takrat, ko je stik z merjenim objektom nezaželjen ali nemogoč, se lahko uporabljajo sevalni termometri, v zadnjem desetletju pa vse bolj prihajajo v ospredje termovizijske kamere. Termovizijska kamera ima mrežo mikrobolometričnih detektorjev (ang.: Focal Plane Array, FPA), ki omogočajo merjenje porazdelitve temperature po površini merjenega telesa. Za razliko od sevalnih termometrov, ki imajo vidno polje okrogle oblike, imajo termovizijske kamere vidno polje pravokotne oblike. Kamera Flir T650sc, ki sem jo uporabil za izvajanje meritev, ima ločljivost 640×480 pikslov. Za natančnejšo določitev temperature merjenega telesa moramo zagotoviti zadostno število pikslov za izračun povprečne temperature. V uvodu je podan zgodovinski pregled odkritij, ki so postavila temelje brezkontaktnemu merjenju temperature, od sevalnih termometrov do termovizijskih kamer. Na točnost merjenja temperatur s termovizijskimi kamerami vpliva več spremenljivk, ki jih moramo upoštevati pri meritvah. Ena od njih, ki je verjetno najmanj raziskana, je vpliv velikosti tarče. V poglavju brezkontaktno merjenje temperature so podani osnovni pojmi od spektra elektromagnetnega valovanja, do infrardečega spektra, toplotnega sevanja, Stefan-Boltzmannovega zakona, Planckovega zakona, emisivnosti do shematske sestave in delovanja termovizijskih kamer. Podrobneje je opisana termovizijska kamera T650sc, ki sem jo uporabljal za izvajanje meritev. Opisan je postopek kalibracije kamere in vpliv velikosti tarče. Sledi poglavje merjenje vpliva velikosti tarče pri termovizijski kameri, kjer je najprej opisano načrtovanje meritev in izdelava zaslonk. Izdelane so bile zaslonke s pravokotnimi in kvadratnimi odprtinami različnih dimenzij, različnega števila in različne medsebojne oddaljenosti. Načrtovano je bilo izvajanje meritev pri različnih črnih telesih na različnih temperaturah. Podane so tudi kratice za lažje označevanje različnih temperatur pri različnih črnih telesih ter različnih zaslonk. Opisana je priprava in postavitev naprav pred merjenjem in sam merilni postopek. Meritve sem opravljal s termovizijsko kamero, ki je bila poravnana z zaslonko in črnim telesom. Z zaslonkami z eno režo sem opravil meritve pri osmih temperaturah različnih črnih teles na petih razdaljah med kamero in zaslonko in ugotovil, da se vpliv velikosti tarče pričakovano kaže kot nižanje izmerjene temperature z manjšanjem širine zaslonk in večanjem razdalje med kamero in zaslonko. Z manjšanjem števila pikslov za izračun povprečne temperature se povečuje negotovost meritve, pri zelo majhnem številu pikslov pa je meritev povprečne temperature nemogoča. Pri enakih dimenzijah rež in kvadratkov je primerjava izmerjenih temperatur pri vseh uporabljenih temperaturah črnih teles, razdaljah in širinah rež oziroma kvadratkov pokazala vedno višje izmerjene temperature pri režah v primerjavi s kvadratki. V to poglavje so vključeni vsi grafični prikazi in primeri termovizijskih slik. V poglavju sklepi so povzete ugotovitve, do katerih sem prišel z obdelavo in interpretacijo termovizijskih slik ter grafičnih prikazov rezultatov. Na koncu diplomskega dela so navedeni uporabljeni viri.

Language:Slovenian
Keywords:vpliv velikosti tarče, termovizija, termovizijska kamera, brezkontaktno merjenje temperature, termogram
Work type:Undergraduate thesis (m5)
Organization:FE - Faculty of Electrical Engineering
Year:2016
Views:859
Downloads:603
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Secondary language

Language:English
Title:Measurement of the size of source effect of a thermal imager
Abstract:
Radiation thermometers can be used for non-contact temperature measurements, when physical contact with a target (measured object) is unwanted or even impossible, but in the last decade the use of a thermographic (thermal) imagers is becoming more and more frequent. A thermographic imager has an array of sensing elements or FPA – focal plane array, which can measure temperature distribution on a target. Unlike radiation thermometers that have a circular field of view, the thermographic imagers have a rectangular field of view. The thermographic imager Flir T650sc, that we used to perform measurements with, has a resolution of 640×480 pixels. It is necessary to provide sufficient number of pixels for more accurate average temperature reading of a measured object. In the chapter Introduction is an overview of discoveries, which set the foundation for non-contact temperature measurements. The accuracy of measured temperature with a thermographic imager is affected by many variables that have to be considered when performing a measurement. The effect, which is probably the least researched, is the size of source effect. The chapter Non-contact temperature measurement describes the basic concept of electromagnetic specter, infrared specter, Stefan-Boltzmann law, Planck law and emissivity. It also specifies parts of a thermographic imager and its functionality. Thermographic imager Flir T650sc, which we used for measurements, is described in detail. The calibration procedure and the size of source effect is also defined. In the chapter Measuring the size of source effect of a thermographic imager planning and making of the aperture tiles is described. The tiles were made with rectangular and square apertures. There were different number of apertures of different sizes and different mutual distance between them. Measurements at different temperatures and with different black bodies were planned. For better comprehension of the aperture tiles, we listed labels for each individual aperture tile. We also labeled different temperatures at different black bodies. The preparation, equipment placement and measuring procedure is described. The measurements were performed with the thermographic imager, which was aligned with an aperture tile and a black body. We performed measurements at eight different temperatures of different black bodies and at five different distances with one rectangular aperture tiles. As expected, the size of source effect was showed as decreasing of the measured temperature when reducing the width of apertures and with increasing the distance between the thermographic imager and an aperture tile. The uncertainty increases with decreasing pixel number for average temperature calculations. The average temperature measurement is impossible with very low number of pixels (less than 3×3 as specified by the manufacturer). We compared measured average temperatures of rectangular and squared apertures of the same size. The results consistently showed higher measured average temperature at rectangular aperture tiles than at square aperture tiles. This chapter also includes all graphic interpretations and examples of the thermographic images. Finally, in chapter Conclusions the findings from processing and interpretation of the thermal images and the graphic interpretation are listed. The thesis also includes the list of references.

Keywords:size of source effect, SSE, thermography, thermographic imager, non-contact temperature measurement, thermograph

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