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Glossary of Thermography Terms

Laser Pyrometer

An infrared radiation thermometer that projects a laser beam to the target uses the reflected laser energy to compute target effective emissivity and automatically computes target temperature (assuming that the target is a diffuse reflector) – not to be confused with laser-aided aiming devices on some radiation thermometers.

Latent Heat

Also called “hidden heat” as heat is added or removed without changing the temperature. The amount of heat required (or released) for a change of phase from solid to liquid and liquid to gas (or vice versa). The latent heat or vaporization is the amount of heat required to change one gram of liquid to vapor without change of temperature. The latent heat of fusion is the amount of heat to melt one gram of solid to liquid with no temperature change.

Line Scan Rate

The number of target lines scanned by an infrared scanner or imager in one second.

Line Scanner, Infrared

An instrument that scans an infrared field of view along a straight line at the target plane in order to collect infrared energy from a line on the target surface, usually done by incorporating one scanning element within the instrument. If the target (such as a sheet or web process) moves at a fixed rate normal to the line scan direction, the result can be displayed as a thermogram.

Lock-in Thermography

A term used to describe an active technique for infrared non-destructive material testing, in which the sample is stimulated with periodically varying (sinusoidally) radiant energy, thus generating heat waves through the material. The resulting thermal images are processed to determine flaw depth and severity. The term Lock-In comes from the fact that excitation, image acquisition and analysis are phase-locked to each other.

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