Multispectral High Temperature Thermography

Abstract

The paper considers the issues of creating high-temperature digital thermographs based on RGB photodetector arrays. It has been shown that increasing the reliability of temperature measurement of bodies with unknown spectral coefficient of thermal radiation can be ensured by optimal selection of the used spectral range and registration of the observed thermal radiation fields in three spectral ranges. The registration of thermal radiation in four or more spectral ranges was found to be inefficient due to the increasing error in temperature determination. This paper presents a method for forming three overlapping spectral regions in the NIR spectral range, which is based on the use of an external spectral filter and a combination of the spectral characteristics of an RGB photodetector array. It is shown that it is necessary to ensure the stability of the solution of the system of three nonlinear equations with respect to the influence of noise. For this purpose, the use of a priori information about the slope factor of the spectral dependence of the thermal radiation coefficient in the selected spectral range for the controlled bodies is proposed. The theoretical results are confirmed by examples of their application in a thermograph based on an array of CMOS RGB photodetectors.

A Review of Thermal Spectral Imaging Methods for Monitoring High-Temperature Molten Material Streams

“…Several multispectral imaging systems operating in the visible-infrared spectrum range were proposed for measurement of temperature distributions on high-temperature targets based on CCD [ 40 , 44 , 45 ], CMOS [ 46 , 47 ], and uncooled MWIR PbSe photodetectors to ensure better coverage of the dynamic range [ 48 ]. However, while one can change the beam-splitter designs to adjust the measured spectral bands, it is not easy to divide the incident light into more than four beams without compromising the system performance.…”

“…Bandpass filters at 450 nm and 500 nm were selected for measurements at high temperatures, while 850 nm and 950 nm filters were chosen for low-temperature measurements. Wójcik et al demonstrated the use of an external bandpass filter and a combination of signals generated by an RGB CMOS matrix to detect thermal radiation simultaneously in three overlapping spectral regions [ 47 ]. It was shown that it is necessary to ensure the stability of the solution of the system of three nonlinear equations with respect to the influence of noise.…”

A Review of Thermal Spectral Imaging Methods for Monitoring High-temperature Molten Material Streams

“…Bandpass filters at 450 nm and 500 nm were selected for measurements at high temperatures, while 850 nm and 950 nm filters were chosen for low temperature measurements. Wojcik et al demonstrated the use of an external bandpass filter and a combination of signals generated by an RGB CMOS matrix to detect thermal radiation simultaneously in three overlapping spectral regions [44]. It is shown that it is necessary to ensure the stability of the solution of the system of three nonlinear equations with respect to the influence of noise.…”