Improvements on Infrared-Camera Calibration for Accurate Surface Temperature Measurements in Arcjet Facilities

Abstract

Ground testing of thermal protection systems play an essential role for understanding the response of candidate materials for thermal shields. Nonintrusive surface temperature measurements are necessary to map the temperature distribution for the correct interpretation of the results obtained in wind-tunnel facilities. An accurate calibration of the infrared camera to be used for a planned experimental campaign on variable transpiration cooling is described in detail. A prototype carbon–carbon cone has been used for both the calibration procedure and experiments. For this application, standard calibration procedures, based on the combined use of blackbody radiators for the calibration of the camera sensor together with tests for emissivity characterization, would not allow for the determination of the accurate surface temperature distribution. This is due to the diversified surface finish and localized defect characteristics of a typical component. The calibration procedure described here, which is based on simultaneous measurements of the local temperature and radiance, allows determination of the local surface temperatures independent of the material emissivity. The calibration curves reveal similar surface thermal response. A higher temperature variance on the calibration curve related to the thermocouple located near the tip of the cone has been detected due to local surface defects.