Abstract
We have developed a real time ultraviolet (UV) imaging system that can visualize both invisible UV light and a visible (VIS) background scene in an outdoor environment. As a UV/VIS image sensor, an organic photoconductive film (OPF) imager is employed. The OPF has an intrinsically higher sensitivity in the UV wavelength region than those of conventional consumer Complementary Metal Oxide Semiconductor (CMOS) image sensors (CIS) or Charge Coupled Devices (CCD). As particular examples, imaging of hydrogen flame and of corona discharge is demonstrated. UV images overlapped on background scenes are simply made by on-board background subtraction. The system is capable of imaging weaker UV signals by four orders of magnitude than that of VIS background. It is applicable not only to future hydrogen supply stations but also to other UV/VIS monitor systems requiring UV sensitivity under strong visible radiation environment such as power supply substations.
Highlights
Imaging ultraviolet radiation during ignition and discharge of excited molecular species is of high value for safety monitoring systems of power plants such as hydrogen stations and transformer substations
Construction of hydrogen stations has already been started in several countries [1], a major concern lies in the fact that hydrogen becomes extremely flammable due to lowering the ignition energy when mixed with air in a relative contents range of 10% to 60% [2]
A worse and reported scenario is that human beings pass through the invisible hydrogen flame caused by accidentally leaking hydrogen from a high pressure tank ignited near the leaking point [1]
Summary
Imaging ultraviolet radiation during ignition and discharge of excited molecular species is of high value for safety monitoring systems of power plants such as hydrogen stations and transformer substations. When cables of power supply stations become degraded, leakage of high power radiation causes corona discharge of air resulting in human hazard and in a fatal accident In these systems, it is important to immediately and accurately detect failing locations that emit weak (possibly 1–10 nW/cm2 ) UV lights superposed on ordinary background daylight (105 lux). Signal processing scheme of subtracting a high level background VIS image in the entire spectral region desired, i.e., from UV to VIS regions, and of pixel circuit configuration from a UV hydrogen flame image overlapped on the background is described. Experimental results of hydrogen flame capable of imaging a weak hydrogen flame signals from four orders of magnitude higher VIS imaging superposed on a high level background is given.
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