Pyrometry using CCD cameras

Abstract

PYROMETRY SPECIFIC IN AERODYNAMIC FACILITIESIn high enthalpy wind tunnels, the surface temper atures should be measured in the range of up to 2000°C. This task is performed with the aid of pyrom etry, i.e. by measurement of intrinsic equilibrium ther mal radiation of investigated object in the visible and near IR spectral ranges.The complexity of optical temperature measure ments in aerodynamic facilities can be attributed, first, to absorption of radiation from investigated object by the windows and mirrors of the optical channel and to their contamination during the tests and, second, to the superposition of flow gas radiation and radiation of the heater from the plenum chamber of the wind tun nel. External illumination, as a rule, limits the mini mal temperature measurable by pyrometry.Pyrometry implies relative measurements, in which the radiation reference etalon with the specified brightness temperature is compared with radiation of the test object. For this purpose, the test model is replaced with the etalon body, and its radiation is detected via the optical system successively with the radiation of the model. Temperature lamps of the SI type (SI6 100, SI8 200, and SI10 300) with the well known dependence of their brightness temperature on the current through the filament are commonly used as the etalon body. The sizes of these lamps allow one to place them on the position of the model in some wind tunnels. Their brightness temperature depen dence on the current is calibrated at wavelength λ = 650 nm at the Rostest Moskva certification center (Moscow). The calibration characteristic of the etalon lamp is recalculated to another wavelength (in case of necessity) using well known tables of the wavelength dependence of the tungsten emissivity [1].Measurement of the surface temperature distribu tion on investigated model surface is a matter of inter est in aerodynamic experiments. For this purpose, the distribution of the model's emission intensity must be measured. A photographic film has been a traditional sensitive element in panoramic pyrometers. However, CCD cameras make it possible to improve substan tially the pyrometry characteristics.CCD CAMERA AS RADIATION DETECTOR CCD cameras are substantially more precise than a photographic film and, in combination with a com puter, provide information on the test object tempera ture directly during an experiment. It should be noted that CCD cameras are more preferable than the less accurate CMOS cameras to measure the light inten sity. In contrast to a photographic film, CCD cameras have a linear response (provided that the amount of Abstract-The method of measurement of the surface brightness temperature distribution in high enthalpy wind tunnels using CCD cameras is described. The problems of the operating wavelength selection, CCD camera metrology, and camera calibration by a black body and temperature lamps, as well as the possibility of LED reference etalon usage for correction of optical channel transmission variation are discussed. It is pro posed to meas...

Remote Monitoring of Radiation Test Temperature Regime at a High-Current Electron Accelerator

“…In particular, continuous remote monitoring of its temperature can be provided by optical pyrometry techniques. Photo-and video cameras with CCD matrices are commonly used for such measurements [5,6]. An additional problem is the presence in the area of measurements of scattered bremsstrahlung radiation, which is formed during the interaction of accelerated electrons with the elements of the output devices of the accelerator, as well as the impact on the measuring devices of electromagnetic radia-tion, which is generated by pulse systems of the accelerator power supply.…”