Tvådimensionell avbildning av temperaturen hos en solid yta: Tvåfärgs pyrometer med en CCD-kamera

Abstract: Two dimensional two-color pyrometer was developed with a 3 CCD for imaging high solid surface temperatures in the research at Luleå University of Technology (LTU). The initial calibrations has been performed with a blackbody radiation source for a temperature range from 900 K up to 1700 K. The camera has been calibrated for how the gain and exposure time affect the pixel intensity (DN). The gain was shown to have an exponential correlation to the pixel intensity. For the exposure time there was a linear correlation towards the pixel intensity where slope and intercept were functions of the energy. The ratio of the green and red pixel intensity for an image is translated into the corresponding temperature. Based on calibration results, algorithm was created to convert the ratio of the two colors to temperature by a polynomial function for gain and exposure time input. This decreased the program computing time compared to if the temperature had to be calculated iteratively from the equations for the both pixel intensities, for each pixel.
The resulting calibration is valid for the temperature range from 1300 K up to 1700 K and is within the target area for the temperature range needed for the research at LTU. The validation of the calculated temperatures delivered a good results from 1100 K up to 1700 K. A pixel intensity in the range 150 < DN < 200 is suggested for the red channel for imaging. The calibration was done for 8 bit images which correspond to a range of pixel intensity from 0 to 255 for the colors red, green and blue (RGB).
A validation experiment was done by imaging the surface of a thermocouple heated by a flat flame burner. The lowest offset between the measured temperature (thermocouple) and the calculated temperature (3CCD) was ca. 25 K and the highest ca. 100 K. The results showed that the evaluated technique of using a 3CCD camera as a two-color pyrometer is valid for measuring solid surface temperature. The calibration will make it possible to measure the surface temperature on fuel particles which will be done during the future research at LTU.