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Understanding Infrared Thermography Reading 3

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Pyroelectric devices have no direct current response, and a basic pyrovidicon<br />

imager 's display will fade when the device is aimed at an unchanging thermal<br />

scene. Early pyrovidicon imagers needed to be panned to retain image<br />

definition.<br />

To enable fixed monitoring, crude, flag type choppers were devised to<br />

interrupt the image at adjustable chop rates. However, this resulted in a<br />

blinking image that was disconcerting to the eye. These choppers have been<br />

replaced by synchronous choppers that chop the image in synchronism with<br />

the electronic scan rate and produce flicker free images on the display.<br />

Pyrovidicon viewers operate well in the 8 to 14 μm atmospheric transmission<br />

window. Operating costs are very low because no cooler or coolant is<br />

required.<br />

Charlie Chong/ Fion Zhang

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