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Advanced Imaging Magazine

Updated: July 8th, 2008 05:26 PM CDT

How to... Use Shortwave Infrared (SWIR) Imaging in Thermal Imaging Applications

SWIR linescan and area cameras and linear arrays from Sensors Unlimited, Goodrich Corporation (Princeton, N.J.)
(Left) A SWIR image shows blackbody source imaged through oven-heated cognac glass, clearly showing both the inside and outside of glass (imaged in full fluorescent room light). (Right) A Thermal microbolometer camera sees only the surface temperature of hot glass when imaged under the same conditions.
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Sensors Unlimited, Goodrich Corporation, developers of shortwave infrared (SWIR) imaging systems based on indium gallium arsenide (InGaAs) technology, has recently developed new machine vision cameras for remote monitoring of hot-end processes, such as glass and metal smelting. Remotely measuring product size, detecting process end-points and defects, controlling process temperatures and inspecting process furnaces are current challenges that are being met by SWIR imaging.

Sensors Unlimitedís linear array cameras feature two ranges of sensitivity, from 0.9 to 1.7 μm and from 1.1 to 2.2 μm, and the SWIR area arrays with sensitivity ranging from 0.9 to 1.7 μm. There are several distinct advantages to using SWIR-InGaAs cameras.

While long-wave infrared (LWIR) cameras (sensitive from 7 to 14 μm) are excellent for detecting thermal patterns around room temperature, they require special, expensive optics made with germanium, sapphire, or silicon. This elite requirement limits the working distance and/or field of view options available to machine vision system integrators. SWIR cameras use readily available and inexpensive photographic or video lenses, making it possible for machine vision integrators to use standard glass safety windows in NEMA-rated enclosures. This is especially important when windows are needed to shield equipment from hot splatter, since these windows often need to be replaced. This can be cost prohibitive when exotic materials are required.

In addition, high-end LWIR cameras are very expensive due to cryogenic cooling requirements, while lower cost microbolometer cameras are limited to frame rates of 30 or 60 Hz. Their calibrations also tend to drift which requires a mechanical shutter to create a new non-uniformity correction every few minutes, reducing long-term reliability and disrupting data acquisition of continuous processes.

InGaAs shortwave infrared imagers offer several other key advantages for machine vision. They:

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