Thermal Imaging Metrology Using High Dynamic Range Near-Infrared Photovoltaic-Mode Camera

Abstract

The measurement of a wide temperature range in a scene requires hardware capable of high dynamic range imaging. We describe a novel near-infrared thermal imaging system operating at a wavelength of 940 nm based on a commercial photovoltaic mode high dynamic range camera and analyse its measurement uncertainty. The system is capable of measuring over an unprecedently wide temperature range; however, this comes at the cost of a reduced temperature resolution and increased uncertainty compared to a conventional CMOS camera operating in photodetective mode. Despite this, the photovoltaic mode thermal camera has an acceptable level of uncertainty for most thermal imaging applications with an NETD of 4–12 °C and a combined measurement uncertainty of approximately 1% K if a low pixel clock is used. We discuss the various sources of uncertainty and how they might be minimised to further improve the performance of the thermal camera. The thermal camera is a good choice for imaging low frame rate applications that have a wide inter-scene temperature range.

Multispectral High Temperature Thermography

“…These methods and the corresponding equipment should provide the necessary reliability of control and ease of use. Non-contact measurement of high temperatures has features associated with a change in the coefficient of thermal radiation of the monitored objects during their heating and fluctuations of the recorded heat fluxes [8][9][10]24,25]. These fluctuations are caused by changes in the surface temperature of the controlled objects due to the effect of convection air flows, as well as the statistical nature of the emission of photons from the heated surface.…”

“…can lead to a substantial change of spectral dependence of thermal radiation coefficient ε (λ) in comparison with the tabular values given in reference books. In addition, other factors related to the observation conditions of the heated surface and the parameters of the photodetector path of thermographic technology will also contribute to error in measuring temperature [8,9].…”

“…In contrast to the thermographic technique of the LWIR range of the spectrum in thermography of the visible and NIR ranges, the spectral density of the brightness of the recorded thermal radiation L (x,y) is changed by several orders of magnitude [7][8][9][10][11]. Adjusting the illumination of the matrix of photodetectors by changing the f-number of the lens of the thermograph camera is unacceptable, since the solid angle of incidence of radiation on the light-sensitive elements changes, and there are deviations of the recorded signals from the calibration dependence.…”