Abstract
The high-cost low-resolution infrared cameras operating in middle infrared spectral ranges are widely used to detect the thermal fields. In this study, a low-cost high-resolution silicon-based sensor camera operating in near infrared spectral ranges is used to perform the observation of the thermal fields on the realistic steel specimen surface. In near-infrared spectral ranges, a small temperature variation led to a large modification in the sensor illumination, inducing acquired images with over saturation or poor dynamic range of gray levels. To address this problem, an algorithm was used to precisely adjust the exposure time to acquire images with constant gray level whatever the temperature evolution is, and then used in heating experiment of a steel specimen. Results showed that images with constant gray level could be acquired during the heating experiment. A special radiometric model was used to perform near-infrared thermography. Based on this radiometric model of steel specimen surface, the thermal fields on steel specimen surface were successfully reconstructed without measuring surface emissivity.
Highlights
Temperature is a very important physical quantity
The results indicated that silicon-based camera can detect a more accurate thermal field than infrared camera
Silicon-based camera has its disadvantage that in near infrared spectral ranges the luminance changes fast with temperature variation, which readily leads to poor quality or bad images
Summary
Temperature is a very important physical quantity. For temperature measurement, many techniques are available, e.g., thermocouple [1, 2], thermistor [3], resistance temperature detector [4], and infrared thermography [5,6,7,8], etc. Teyssieux et al [19,20,21] indicated that the disturbance radiation from surrounding objects is slight and can be negligible in near infrared spectral range, while the disturbance radiation from surrounding objects is obvious in middle infrared spectral range Both infrared camera and silicon-based camera were used to measure temperature distribution of the object surface with non-homogeneous emissivity by Rotrou et al [22]. Silicon-based camera has its disadvantage that in near infrared spectral ranges the luminance changes fast with temperature variation, which readily leads to poor quality or bad images (oversaturation or poor dynamic range of gray levels) This phenomenon makes the measurement of thermal fields impossible when the temperature changes, especially the high temperature application
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