| 摘要 |
An apparatus for monitoring an access portal through an enclosure around a hazard comprises a line-scan camera mounted above the portal so that its linear field of view extends along a generally opposite threshold of the portal and can detect electromagnetic radiation reflected from an object passing through the portal. The apparatus distinguishes signals from the camera corresponding to items that are intended to pass through the portal for example on a conveyor from signals corresponding to items, particularly intruders that are not intended to pass through the portal. The apparatus preferably comprise an elongate sodium discharge lamp mounted above the portal and provided with a reflector so that monochromatic light therefrom is concentrated in a narrow strip extending along the threshold and the camera is sensitive only to this monochromatic light.
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