Quantitative thermal imaging using single-pixel Si APD and MEMS mirror

Accurate quantitative temperature measurements are difficult to achieve using focal-plane array sensors. This is due to reflections inside the instrument and the difficulty of calibrating a matrix of pixels as identical radiation thermometers. Size-of-source effect (SSE), which is the dependence of an infrared temperature measurement on the area surrounding the target area, is a major contributor to this problem and cannot be reduced using glare stops. Measurements are affected by power received from outside the field-of-view (FOV), leading to increased measurement uncertainty. In this work, we present a micromechanical systems (MEMS) mirror based scanning thermal imaging camera with reduced measurement uncertainty compared to focal-plane array based systems. We demonstrate our flexible imaging approach using a Si avalanche photodiode (APD), which utilises high internal gain to enable the measurement of lower target temperatures with an effective wavelength of 1 µm and compare results with a Si photodiode. We compare measurements from our APD thermal imaging instrument against a commercial bolometer based focal-plane array camera. Our scanning approach results in a reduction in SSE related temperature error by 66 °C for the measurement of a spatially uniform 800 °C target when the target aperture diameter is increased from 10 to 20 mm. We also find that our APD instrument is capable of measuring target temperatures below 700 °C, over these near infrared wavelengths, with D* related measurement uncertainty of ± 0.5 °C

Quantitative traceable temperature measurement using novel thermal imaging camera

Conventional thermal imaging cameras, based on focal-plane array (FPA) sensors, exhibit inherent problems: such as stray radiation, cross-talk and the calibration uncertainty of ensuring each pixel behaves as if it were an identical temperature sensor. Radiation thermometers can largely overcome these issues, comprising of only a single detector element that can be optimised and calibrated. Although the latter approach can provide excellent accuracy for single-point temperature measurement, it does not provide a temperature image of the target object. In this work, we present a micromechanical systems (MEMS) mirror and silicon (Si) avalanche photodiode (APD) based single-pixel camera, capable of producing quantitative thermal images at an operating wavelength of 1 μm. This work utilises a custom designed f-theta wide-angle lens and MEMS mirror, to scan +/− 30° in both x- and ydimensions, without signal loss due to vignetting at any point in the field of view (FOV). Our single-pixel camera is shown to perform well, with 3 °C size-of-source effect (SSE) related temperature error and can measure below 700 °C whilst achieving ± 0.5 °C noise related measurement uncertainty. Our measurements were calibrated and traceable to the International Temperature Scale of 1990 (ITS-90). The combination of low SSE and absence of vignetting enables quantitative temperature measurements over a spatial field with measurement uncertainty at levels lower than would be possible with FPA based thermal imaging cameras

DISTRIBUTED FIBER-OPTIC TEMPERATURE SENSORS FOR APPLICATIONS IN THE STEEL INDUSTRY

Steelmaking facilities require continuous temperature measurements throughout the manufacturing process to ensure consistent product quality and high productivity. Motivated by the limitations of conventional temperature sensors, distributed fiber-optic sensors (DFOS) were developed and deployed for various applications in the steel industry. Fiber-optic sensors offer various advantages over conventional sensors, such as the miniaturized size of the optical fiber, immunity to electromagnetic interferences, capability for multiplexing and distributed sensing, and the ability to withstand harsh environments. Firstly, high-resolution Rayleigh backscattering based DFOS were demonstrated as potential solutions for temperature measurements in steelmaking processes by performing experimental simulations. Additionally, aluminum casting experiments were conducted to demonstrate the measurement capability of DFOS in solidifying metal alloys. Temperatures exceeding 700 ℃ were measured at sub-millimeter spatial resolution (~ 0.65 mm) and at milliseconds sampling speeds. Moreover, a novel dip testing paddle was developed employing a copper mold instrumented with optical fiber. The instrumented mold was used to perform steel dip tests in a 200 lb induction furnace in a foundry laboratory. The results obtained from temperature measurements provided strong evidence that the dip testing paddle can be a useful apparatus for the investigation of the fundamental reactions occurring in a continuous casting mold. The present study demonstrated that DFOS can be transformative to the steel industry by enabling efficient process control, reducing energy and maintenance costs, improving the safety of equipment and workers, and enhancing the quality and yield of metal products --Abstract, p. i

The Study of Fire Spread on an Inclined Wooden Surface by Multiple Spectrum Imaging Systems and Diagnostical Techniques

Fire disaster, as an unavoidable threat around the world, caused millions of loss of living beings and properties. To minimise the damage that fire disaster causes, the prediction of fire spread is significant. Due to the burning of wood is a series of complicated processes, the study of fire spread along the wood surface is far from complete. To comprehensively understand the mechanism of wood combustion as well as the fire spread, a systematically study is necessary. With the development of digital cameras and computer science, the vision systems based on the digital camera become a useful tool for measurement and visualisation. In this work, the fire spread on inclined wooden rod surface is systematically studied based on the vison systems. An original designed imaging system that synchronises visible, schlieren, and thermal imaging systems is developed. The various diagnostical techniques, including the temperature measurements by two-colour method and thermal imaging, optical flow motion estimation, and selective enhancement technique are developed along with the imaging system. Rely on the imaging system that developed in this study, the burning ability, temperature of the wooden surface and flame, the dim blue flame and the invisible hot gas flow can be visualised simultaneously. The first contribution of this work is the developed pyrometers which are based on two methods: the first one is the two-colour method, which relies on the response ratio between two selected wavelengths. This method is used for measuring the soot flame temperature. The second pyrometer is based on thermal imaging, which uses a narrow band wavelength thermal image with known emissivity. It is used for reading the temperature of the wood surface. With the instruments developed in this work, the flame temperature and surface temperature of the burning wood can be monitored at the same time. Based on the imaging system and diagnostical techniques, the fire spread on wooden rods surface that inclined at various angles is investigated. It is first found in this work both the flame and fire plume would have geometry change at the inclination surface. Besides, with the help of the optical flow method, the minor fluctuate (<2mm/s) of the flame and hot flow can be detected and used to analyse the burning phenomena. Another finding is the essential role of underneath preheating on sustaining the burning and spreading the fire. The pyrolysis zone, as well as the preheating zone, have been illustrated and visualised by synchronising the blue flame with the schlieren image by the first time. Furthermore, with involving the thermal imaging system, the preheating length underneath the burning rod is calculated and shows a monotonically increase with the increasing angle. Moreover, this work introduces a novel method to measure the flame attachment phenomenon quantitatively by using enhanced thermal image. The effects of cross-wind on the burning of wood are investigated systematically with the imaging system. The main finding is that under the low speed of cross-wind, the burning and fire spread are enhanced, while they are decreased under the high speed of the wind. With the help of the multiple spectrum imaging, the mechanisms of the wood combustion under wind condition has been studied and visualised. This new imaging system with developed diagnostical techniques is a useful tool for investigating the burning of wood and fire propagation. The findings in this works could help enhance the understanding of the fire protection and optimise the strategy both in fire protection and fire extinction